Author Topic: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier  (Read 46791 times)

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Offline EEVblog

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EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« on: January 07, 2016, 07:46:11 am »
Dave reverse engineers the XuanZu X2-U808 Hi-Fi Headphone Amplifier to see if the valves actually do anything.
What is the circuit topology?
E180F (6J9) pentode valve datasheet: http://frank.pocnet.net/sheets/009/e/E180F.pdf
Doug Ford's Microphone design series: http://www.youtube.com/playlist?list=PLvOlSehNtuHv98KUcud260yJBRQngBKiw

 

Offline Radio Tech

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #1 on: January 07, 2016, 10:18:49 am »
I was really surprised to see that the tubes actually did something in the circuit. As you said it could have worked without them.
Nice reversal on the circuit Dave.

Offline c4757p

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #2 on: January 07, 2016, 10:27:24 am »
For the little bit that it's worth, the tubes are doing something if you want "tube distortion", even a follower configuration will distort (though perhaps with a slightly different profile than a voltage amplifier).

Might be interesting to look at an FFT of the output. (Disclaimer, I haven't had a chance to watch all the way through yet, I got about halfway...)
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Offline thomastheo

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #3 on: January 07, 2016, 10:42:20 am »
I was really hoping for a little high voltage boost circuit, and a proper tube based amplifier. Not because it would have better audio output than a set of op-amps, because i don't buy all that nonsense, but because it would be a great little piece of nostalgia. I would totally buy one if it was, novelty or not, but alas.
 

Offline AF6LJ

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #4 on: January 07, 2016, 10:49:54 am »
Drawing an  analogy to a J-FET is simply wrong.
A more apt analogy would be a MOS-FET since there is an insulator between the elements like in a vacuum tube.


Sorry Dave Ya got it wrong.
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Offline Ampere

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #5 on: January 07, 2016, 10:55:06 am »
I'm a bit disappointed that they're just being used as buffers (and noise generators), but at least I learned something about tubes.
 

Offline AF6LJ

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #6 on: January 07, 2016, 11:09:23 am »
Not the kind of thing I would waste my money on.
Yah it's Cute, but so much of the electronic trash that comes out of China also has a cuteness factor.
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Online Richard Crowley

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #7 on: January 07, 2016, 11:09:41 am »
I have found it to be a pretty reliable indicator that if they put an LED under the fire-bottle to "light it up", then they are going for sizzle and there's no steak there.  Move on, nothing to see here.   :=\  (second time I've used that emoticon in 10 minutes after never using it before.)
 

Offline gadget73

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #8 on: January 07, 2016, 11:17:56 am »
yay for Chinese numbering.  Same "number", but completely different part thats not even remotely close to the original.  Nothing like swapping a triple triode for a sharp cutoff pentode and sticking the same number on it for confusion reasons.

Honestly the reason that solid state makes no sense to me is because I get electron flow.  "conventional" flow is backwards and makes no sense in my head. 
« Last Edit: January 07, 2016, 11:24:14 am by gadget73 »
 

Offline AF6LJ

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #9 on: January 07, 2016, 11:43:47 am »
yay for Chinese numbering.  Same "number", but completely different part thats not even remotely close to the original.  Nothing like swapping a triple triode for a sharp cutoff pentode and sticking the same number on it for confusion reasons.

Honestly the reason that solid state makes no sense to me is because I get electron flow.  "conventional" flow is backwards and makes no sense in my head.

I discovered a long time ago it makes no difference which way the little packets of energy go, it all works out just fine. :)
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Offline jolshefsky

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #10 on: January 07, 2016, 11:54:00 am »
If my really quick look is correct, it looks like you can remove the valves and jumper pin 2 (control grid) to pin 3 (cathode) and get a much lower power, halfway decent headphone amp.
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Offline V42bis

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #11 on: January 07, 2016, 12:14:12 pm »
If it's not torn down yet, try putting a couple of square wave through it, say 2KHz to check the upper frequency response, should not have significant under or over shoot. Then a 20hz square wave and it should not have signify tilt.

 

Offline N2IXK

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #12 on: January 07, 2016, 12:17:50 pm »
yay for Chinese numbering.  Same "number", but completely different part thats not even remotely close to the original.  Nothing like swapping a triple triode for a sharp cutoff pentode and sticking the same number on it for confusion reasons.

The tubes are actually Russian tubes, which can be translated from Cyrillic as 6Sh9P or 6J9P.  Equivalent to the European E180F or the US type 6688.

Original USSR datasheet:

http://www.magictubes.ru/sprav/pdf/6j9p.pdf
« Last Edit: January 07, 2016, 12:21:27 pm by N2IXK »
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Offline max666

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #13 on: January 07, 2016, 12:21:07 pm »
Drawing an  analogy to a J-FET is simply wrong.
A more apt analogy would be a MOS-FET since there is an insulator between the elements like in a vacuum tube.


Sorry Dave Ya got it wrong.

No I think you got it wrong, if the control grid voltage would become positive a grid current would flow, just like in a J-FET.
 

Offline rrinker

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #14 on: January 07, 2016, 12:22:33 pm »
 My favorite is that one Gigabyte PC motherboard that had a single tube audio amp on it. Talk about silly...


 

Offline gadget73

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #15 on: January 07, 2016, 12:39:41 pm »

I discovered a long time ago it makes no difference which way the little packets of energy go, it all works out just fine. :)

Also just too many parts to keep track of :) 

24v K-A and a cathode follower arrangement?  Whats the point?  It would give lower output impedance, but feeding into an op-amp its not like that would be required. Not enough voltage to make any useful gain anyway.  Wonder how far out of the linear operating range it is. 
 

Offline AF6LJ

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #16 on: January 07, 2016, 12:51:46 pm »

I discovered a long time ago it makes no difference which way the little packets of energy go, it all works out just fine. :)

Also just too many parts to keep track of :) 

24v K-A and a cathode follower arrangement?  Whats the point?  It would give lower output impedance, but feeding into an op-amp its not like that would be required. Not enough voltage to make any useful gain anyway.  Wonder how far out of the linear operating range it is.
In my opinion there is no point, That is not a good tube for a cathode follower, the designer is not taking advantage of the high input impedance a vacuum tube offers, and as you pointed out the plate voltage (B+) is too low.

The designer isn't even trying to prove something.

Why not?
build a 30W headphone amplifier using all tubes, no output transformer, using an output differential amplifier with cathode output. (to keep the voltage and impedance low)? Run it on say............125V regulated(+/- 65.5V).

That would be a concept amplifier worth building, if for no other reason than to prove the idea. :)
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Offline retrolefty

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #17 on: January 07, 2016, 12:52:18 pm »
My favorite is that one Gigabyte PC motherboard that had a single tube audio amp on it. Talk about silly...

 I remember seeing a picture of that, couldn't believe it when I first saw it, but then I remembered the golden ear crowd. Suspect it wasn't a big seller. You know that could be somewhat of a collectors item.
 

Offline AF6LJ

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #18 on: January 07, 2016, 12:53:00 pm »
My favorite is that one Gigabyte PC motherboard that had a single tube audio amp on it. Talk about silly...

I wish I had three hands....
This is a triple face palm.  :palm: :palm: :palm:
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Offline retrolefty

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #19 on: January 07, 2016, 12:56:14 pm »

I discovered a long time ago it makes no difference which way the little packets of energy go, it all works out just fine. :)

Also just too many parts to keep track of :) 

24v K-A and a cathode follower arrangement?  Whats the point?  It would give lower output impedance, but feeding into an op-amp its not like that would be required. Not enough voltage to make any useful gain anyway.  Wonder how far out of the linear operating range it is.
In my opinion there is no point, That is not a good tube for a cathode follower, the designer is not taking advantage of the high input impedance a vacuum tube offers, and as you pointed out the plate voltage (B+) is too low.

The designer isn't even trying to prove something.

Why not?
build a 30W headphone amplifier using all tubes, no output transformer, using an output differential amplifier with cathode output. (to keep the voltage and impedance low)? Run it on say............125V regulated(+/- 65.5V).

That would be a concept amplifier worth building, if for no other reason than to prove the idea. :)

 Why 30 watts, not many headphones can accept even peaks at that level? About the only thing that might differentiate a 'headphone amp' form other audio amps is that it might be designed to only work at the higher output impedance of most headsets.
 

Offline AF6LJ

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #20 on: January 07, 2016, 01:13:19 pm »

I discovered a long time ago it makes no difference which way the little packets of energy go, it all works out just fine. :)

Also just too many parts to keep track of :) 

24v K-A and a cathode follower arrangement?  Whats the point?  It would give lower output impedance, but feeding into an op-amp its not like that would be required. Not enough voltage to make any useful gain anyway.  Wonder how far out of the linear operating range it is.
In my opinion there is no point, That is not a good tube for a cathode follower, the designer is not taking advantage of the high input impedance a vacuum tube offers, and as you pointed out the plate voltage (B+) is too low.

The designer isn't even trying to prove something.

Why not?
build a 30W headphone amplifier using all tubes, no output transformer, using an output differential amplifier with cathode output. (to keep the voltage and impedance low)? Run it on say............125V regulated(+/- 65.5V).

That would be a concept amplifier worth building, if for no other reason than to prove the idea. :)

 Why 30 watts, not many headphones can accept even peaks at that level? About the only thing that might differentiate a 'headphone amp' form other audio amps is that it might be designed to only work at the higher output impedance of most headsets.

In a word "Headroom" but even 10W would be enough.
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Offline jitter

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #21 on: January 07, 2016, 01:39:45 pm »
Dave reverse engineers the XuanZu X2-U808 Hi-Fi Headphone Amplifier to see if the valves actually do anything.
What is the circuit topology?
E180F (6J9) pentode valve datasheet: http://frank.pocnet.net/sheets/009/e/E180F.pdf
Doug Ford's Microphone design series: http://www.youtube.com/playlist?list=PLvOlSehNtuHv98KUcud260yJBRQngBKiw

A lot of wank indeed. Made for the true audiophile that sees the tubes/valves and just "knows" that these must sound good.
Tell the same people that it has SMPSs in there, and it'll fall off it's pedestal in the blink of an eye.

Other than guitar amps, which are all about distortion, and for good looks (tubes just look cool without the blue LEDs), I see very little use for hollow state amplifiers.
 

Offline retrolefty

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #22 on: January 07, 2016, 01:44:36 pm »
Dave reverse engineers the XuanZu X2-U808 Hi-Fi Headphone Amplifier to see if the valves actually do anything.
What is the circuit topology?
E180F (6J9) pentode valve datasheet: http://frank.pocnet.net/sheets/009/e/E180F.pdf
Doug Ford's Microphone design series: http://www.youtube.com/playlist?list=PLvOlSehNtuHv98KUcud260yJBRQngBKiw


A lot of wank indeed. Made for the true audiophile that sees the tubes/valves and just "knows" that these must sound good.
Tell the same people that it has SMPSs in there, and it'll fall off it's pedestal in the blink of an eye.

Other than guitar amps, which are all about distortion, and for good looks (tubes just look cool without the blue LEDs), I see very little use for hollow state amplifiers.

 Still popular and useful for HF Kilowatt RF amplifiers used on the ham radio bands.
 

Offline BobC

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #23 on: January 07, 2016, 01:58:34 pm »
So, in our world of programmable analog circuit arrays and perfect rail-to-rail opamps, when would you *need* to use a tube?  When does using silicon not make sense?

I've been fortunate to have worked in a wide variety of fields, including radiation monitoring.  Some of the sensors provide signals in the microvolt/nanoamp  range, and local gain is needed before forwarding the signal elsewhere.  But when the sensor is near the center of an operating nuclear reactor, gain can be tough to find.  How to get local gain?

Specialty tubes to the rescue!  A vacuum is naturally radiation-resistant. But careful selection of materials is needed to make a tube that will have a useful lifetime and still work at high temperatures in the presence of massive levels of ionizing and neutron radiation.  It turned out that minor process tweaks to existing tubes did the trick, and a dual-stage high-gain amp provided all the gain needed.  (Our work was also used on satellites operating in the van Allen belts.)

What finally killed tubes in this application (decades after tubes disappeared everywhere else) was their accelerated aging.  Inside a nuclear reactor, a lifespan of a 7 years often isn't good enough.

So we had to find ways to get the raw sensor signal away from the reactor to external amplifiers.  The cost was moved from the tubes to ultra-low-loss cabling, and the signal was fed to what was basically a logarithmic nano-ammeter.

Fun all the way, no matter how you slice it.  The conversion to a nearly all-digital system (reducing the circuitry between the ADC and the sensor) was boring in comparison.
 

Online Brumby

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #24 on: January 07, 2016, 02:00:47 pm »
Just one word .... context.
 

Online helius

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #25 on: January 07, 2016, 02:23:51 pm »
So, in our world of programmable analog circuit arrays and perfect rail-to-rail opamps, when would you *need* to use a tube?  When does using silicon not make sense?
http://spectrum.ieee.org/semiconductors/devices/the-quest-for-the-ultimate-vacuum-tube
 

Offline ConKbot

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #26 on: January 07, 2016, 02:58:43 pm »
I saw it was a pentode and though "WTf I though you used single end triodes for audiophile cred, pentodes and push-pulls got the distortion too low" 

Then dave had the schematic drawn out...   :-DD
 

Offline boffin

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #27 on: January 07, 2016, 03:18:54 pm »
Could you just pull the valve and connect the grid to the anode?

Boffin at play https://snafu.ca/
 

Offline Pentium100

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #28 on: January 07, 2016, 03:20:05 pm »
I saw it was a pentode and though "WTf I though you used single end triodes for audiophile cred, pentodes and push-pulls got the distortion too low" 

Then dave had the schematic drawn out...   :-DD

Pentode in SE usually has higher distortion. Connecting it in ultra-linear mode lowers the output power and distortion, triode mode is lowest power and lowest distortion.

A JFET has IV curves almost exactly like those of a pentode, however, I do not know of any semiconductor device that has the IV curves of a triode.
 

Online Brumby

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #29 on: January 07, 2016, 03:23:28 pm »
Could you just pull the valve and connect the grid to the anode?

Not in this design.  The anode goes to the positive rail.

You'd have to connect the grid to the cathode - but, yes, your basic idea is ok.

Except for one thing - the signal would no longer go through a valve, removing the premise for it being there.
 

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #30 on: January 07, 2016, 03:28:55 pm »
The fact that the valve doesn't effectively do anything isn't 'relevant' to the target market.  The fact that the signal does, in fact, pass through a valve is enough for them.


Also, I find the ultra low distortion figure absolutely hilarious when that target market is after the valve 'sound'.
 

Offline boffin

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #31 on: January 07, 2016, 04:06:23 pm »
Could you just pull the valve and connect the grid to the anode?

Not in this design.  The anode goes to the positive rail.

You'd have to connect the grid to the cathode - but, yes, your basic idea is ok.

Except for one thing - the signal would no longer go through a valve, removing the premise for it being there.
Yes, I meant Cathode; damn electron flow...
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Offline ConKbot

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #32 on: January 07, 2016, 04:52:51 pm »
I saw it was a pentode and though "WTf I though you used single end triodes for audiophile cred, pentodes and push-pulls got the distortion too low" 

Then dave had the schematic drawn out...   :-DD

Pentode in SE usually has higher distortion. Connecting it in ultra-linear mode lowers the output power and distortion, triode mode is lowest power and lowest distortion.

A JFET has IV curves almost exactly like those of a pentode, however, I do not know of any semiconductor device that has the IV curves of a triode.
Yeah I'm not up on valve amps, I thought I had read somewhere that as they progressed the distortion got down quite low (I forget how, thought it was pentodes, apparently not. ) but in doing so, lost the tube amp 'sound'
 

Online blueskull

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #33 on: January 07, 2016, 04:58:54 pm »
yay for Chinese numbering.  Same "number", but completely different part thats not even remotely close to the original.  Nothing like swapping a triple triode for a sharp cutoff pentode and sticking the same number on it for confusion reasons.

Honestly the reason that solid state makes no sense to me is because I get electron flow.  "conventional" flow is backwards and makes no sense in my head.

All Chinese tubes made before 80s are direct copy of Soviet tubes, hence having soviet part numbers.

They are named in xyz form, where x and z are numbers, same to the numbers in the Soviet version, where y is an English letter, that corresponds to a Russian letter.
 

Online blueskull

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #34 on: January 07, 2016, 05:04:47 pm »
Tubes can affect audio characteristics a lot, pretty much by introducing harmonics and compress input level.

Some people found listening to slightly distorted music feels more comfortable, hence the popularity of tube amp.

Personally I prefer exact sound reproduction, not distorted, hence I use high end DAC coupled with monitor grade IEM.

But I know a few people prefer tube or JFET amplified sound that introduces harmonics. They claim it sounds warmer.

There are even commercial VST plugins to digitally introduce tube effects to a piece of sound track.
 

Offline coppice

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #35 on: January 07, 2016, 05:15:36 pm »
Personally I prefer exact sound reproduction, not distorted, hence I use high end DAC coupled with monitor grade IEM.
What do you consider exact sound reproduction? Our hearing is tied in with our vision, so without the original images we don't hear things as we would in real life. The McGurk effect is the most famous example of this, but it isn't just a speech issue. It happens with musical instruments and other sound sources too. Also, those inner ear monitors might reproduce the super low bass from the lowest pedals of a cathedral organ, but they won't give you that punch in the chest you feel in the actual cathedral, so that's not faithful reproduction, either.
« Last Edit: January 07, 2016, 05:28:29 pm by coppice »
 

Online Brumby

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #36 on: January 07, 2016, 05:26:06 pm »
Could you just pull the valve and connect the grid to the anode?

Not in this design.  The anode goes to the positive rail.

You'd have to connect the grid to the cathode - but, yes, your basic idea is ok.

Except for one thing - the signal would no longer go through a valve, removing the premise for it being there.
Yes, I meant Cathode; damn electron flow...

Nice try, but I'll call you on that.   :D
 

Online blueskull

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #37 on: January 07, 2016, 05:26:38 pm »
Personally I prefer exact sound reproduction, not distorted, hence I use high end DAC coupled with monitor grade IEM.
What do you consider exact sound reproduction? Our hearing is tied in with our vision, so without the original images we don't hear things as we would in real life. The McGurk effect is the most famous example of this, but it isn't just a speech issue. It happens with musical instruments and other sound sources too. Also, those inner ear monitors might reproduce the super low bass from the lowest pedals of a cathedral organ, but they won't give you that punch in the chest you feel in the actual cathedral, so that's notfaithful reproduction, either.

My standard:

DAC and HPA does not introduce any flavor, headphone has flat response compared to spl.
 

Offline mikerj

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #38 on: January 07, 2016, 08:30:21 pm »
A big fail is that any ripple on the -12v switcher rail is inejcted into the input of the op-amp stages, something you can clearly see on the scope when the amp is powered up.  I was hoping Dave was going to put the scope into FFT mode jut to see what kind of crap was coming out of the valve compared to the output of the sig gen.
 

Offline Salas

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #39 on: January 07, 2016, 08:45:14 pm »
How high is the anode voltage used and how is it created in this headphones amp?
 

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #40 on: January 07, 2016, 09:06:29 pm »
I think we are all missing the point here. This was sold for about 50 bucks. No true "audiophile" would buy a 50 dollar headphone amp, so this is not "audiophile quality".

Now, if you would sell the same thing for 500 dollars, it would be a different story...
 

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #41 on: January 07, 2016, 09:21:40 pm »
I wonder how much these cheap ceramic caps in the signal path will improve the listening experience...
 

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #42 on: January 07, 2016, 09:38:02 pm »
Dave, didn't you have some dynamic spectral analyzer? It might be interesting to look with it at what comes in vs what comes out.
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Offline G7PSK

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #43 on: January 07, 2016, 10:12:45 pm »
Funny thing is that valve is not in my 1969 Mullard data book, but it is the 1959 book under miscellaneous but there is no data.
 

Offline mikerj

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #44 on: January 07, 2016, 10:14:04 pm »
How high is the anode voltage used and how is it created in this headphones amp?

About 24v total (-12 on cathode, +12 on anode) and two small switching regulators are used to create the voltage rails.
 

Offline ciccio

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #45 on: January 07, 2016, 10:43:44 pm »
I don't want to discuss the electronic design or the performance of this toy.
It obviously was designed for a market objective, and the design is done reasonably well.
What i discuss is what none of the above posters noted:
this toy (and a lot of other tube audio gear on the market) is designed and built without any consideration about product safety.
EN60065 (safety requirement for audio, video and similar electronic apparatus) and it's equivalent regulations are violated in at least 2 points:
- There are HOT parts accessible to the user (the tubes)
- There is a mechanical danger of breaking the glass tubes and cut yourself with the glass.

This toy should not be sold, even in China.

Best regards
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Offline timb

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #46 on: January 07, 2016, 11:08:31 pm »

- There are HOT parts accessible to the user (the tubes)
- There is a mechanical danger of breaking the glass tubes and cut yourself with the glass.

This toy should not be sold, even in China.

Best regards

Well, you guys heard ciccio, mains voltage and glass objects are dangerous!

We better get rid of wall outlets, since the HOT parts are accessible to users... We should also do away with glass cups and bottles as we could cut ourselves!

In fact, personal Faraday cages and sippy cups should be mandatory for everyone to prevent electrocution or severe gashes!
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Offline dr.diesel

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #47 on: January 07, 2016, 11:17:49 pm »
EN60065 (safety requirement for audio, video and similar electronic apparatus) and it's equivalent regulations are violated in at least 2 points:
- There are HOT parts accessible to the user (the tubes)
- There is a mechanical danger of breaking the glass tubes and cut yourself with the glass.

This toy should not be sold, even in China.

 :palm:

Let's not dumb down society even more, complete fail.

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #48 on: January 07, 2016, 11:39:26 pm »

I discovered a long time ago it makes no difference which way the little packets of energy go, it all works out just fine. :)

Also just too many parts to keep track of :) 

24v K-A and a cathode follower arrangement?  Whats the point?  It would give lower output impedance, but feeding into an op-amp its not like that would be required. Not enough voltage to make any useful gain anyway.  Wonder how far out of the linear operating range it is.
In my opinion there is no point, That is not a good tube for a cathode follower, the designer is not taking advantage of the high input impedance a vacuum tube offers, and as you pointed out the plate voltage (B+) is too low.

The designer isn't even trying to prove something.

Why not?
build a 30W headphone amplifier using all tubes, no output transformer, using an output differential amplifier with cathode output. (to keep the voltage and impedance low)? Run it on say............125V regulated(+/- 65.5V).

That would be a concept amplifier worth building, if for no other reason than to prove the idea. :)

 Why 30 watts, not many headphones can accept even peaks at that level? About the only thing that might differentiate a 'headphone amp' form other audio amps is that it might be designed to only work at the higher output impedance of most headsets.

Not many headphones can accept 30W RMS, but 30W peaks? Sure.
 

Online Fungus

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #49 on: January 07, 2016, 11:41:07 pm »
No frequency response/distortion/noise measurements?  Am leaving disappointed.

And why would you "buffer" something that's going to be fed into an op-amp? The op-amp impedance isn't high enough?  :-//

Still, I guess I'm missing the point. I'm not the target market for this. I'm sure looking at glowing tubes will improve the sound quality for many people.


« Last Edit: January 07, 2016, 11:45:43 pm by Fungus »
 

Offline retrolefty

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #50 on: January 08, 2016, 12:24:45 am »
No frequency response/distortion/noise measurements?  Am leaving disappointed.

And why would you "buffer" something that's going to be fed into an op-amp? The op-amp impedance isn't high enough?  :-//

Still, I guess I'm missing the point. I'm not the target market for this. I'm sure looking at glowing tubes will improve the sound quality for many people.

 Well at least if a buyer of this amp was expecting and did hear a difference then at least he/she arrived at that conclusion for a whole lot less cash then the 'true believers' that spend ridiculous amounts of money chasing their expectations.

 

Offline ciccio

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #51 on: January 08, 2016, 12:27:37 am »
Well, you guys heard ciccio, mains voltage and glass objects are dangerous!

We better get rid of wall outlets, since the HOT parts are accessible to users... We should also do away with glass cups and bottles as we could cut ourselves!

In fact, personal Faraday cages and sippy cups should be mandatory for everyone to prevent electrocution or severe gashes!

Hope you are joking.. Glass cups are not electronic devices. There is NOT a safety regulation for them...
Wall outlets in any country (outside US and the other who use US type sockets) do not have user accessible parts.
If you want to have  accessible LIVE part in your house, that's you choice, but no manufacture should be allowed to sell them to you. 

HOT for me refers to temperature, not mains voltage  (in fact the max voltage inside that amp is 12 V dc). Tubes are hot, a child can burn his hands by  simply touching it, and the blue LED is an attraction.

Serious manufacturers of tube equipment install a perforated shield over the tubes, such as the one in the  attachment (randomly chosen on the NET).
If the customer removes it to have his evening orgasm whilst looking at red tubes, it is his choice, but the manufactures demonstrates his competence in installing it by default.
Other (don't want to say less serious) do not install any protection and maybe don't even have the money for buying a copy of the relevant safety specification.
When a problem arise, you will discover that the did not have the money for product's liability assurance too.


Ciccio

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Offline N2IXK

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #52 on: January 08, 2016, 12:34:03 am »
Those tubes aren't going to get more than warm running at 24V.  Certainly not hot enough to be considered a burn hazard.

The perforated shields are needed over POWER amplifiers, which have output tubes which actually get hot in use.
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Offline c4757p

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #53 on: January 08, 2016, 12:40:55 am »
Oh no, a child might burn his hand on a hot thing or cut himself on a sharp thing! REGULATE! :scared:



Don't grab hot things, don't smack glass things, and teach your children the same. FFS people.

Unfortunately I think we still need to be fairly careful with high voltages. A lot of people don't understand electricity very well, and it can be an invisible hazard... though I still think some countries overdo it on the regulations there, dunno. Not sure exactly how much I think is appropriate there. But hot and sharp? Come on.
« Last Edit: January 08, 2016, 12:46:25 am by c4757p »
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Offline @rt

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #54 on: January 08, 2016, 12:46:57 am »
Well you still know if the operator at the other end has valve audio preamp even if you have a solid state receiver.

Similarly an old 50’s SW valve radio is the best audio for HF I’ve yet heard.

Still popular and useful for HF Kilowatt RF amplifiers used on the ham radio bands.
 

Online NANDBlog

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #55 on: January 08, 2016, 12:50:29 am »
My favorite is that one Gigabyte PC motherboard that had a single tube audio amp on it. Talk about silly...

I wish I had three hands....
This is a triple face palm.  :palm: :palm: :palm:
While it is possibly waste of natural resourses, there are dual triode tubes, like the 12AX7. That can be used to to amplify the DAC output, going to the headphone out.
 

Offline dr.diesel

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #56 on: January 08, 2016, 12:51:27 am »
Oh no, a child might burn his hand on a hot thing or cut himself on a sharp thing! REGULATE! :scared:

Yup, regulate, and where you can't sue to make millions.  Pretty much sums up today's philosophy, pathetic and depressing.

Offline mikerj

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #57 on: January 08, 2016, 01:23:28 am »
Hope you are joking.. Glass cups are not electronic devices. There is NOT a safety regulation for them...
Wall outlets in any country (outside US and the other who use US type sockets) do not have user accessible parts.
If you want to have  accessible LIVE part in your house, that's you choice, but no manufacture should be allowed to sell them to you. 

HOT for me refers to temperature, not mains voltage  (in fact the max voltage inside that amp is 12 V dc). Tubes are hot, a child can burn his hands by  simply touching it, and the blue LED is an attraction.

We must also ban all  incandescent lamps, cookers, toasters, heaters, kettles etc.  Use of a soldering iron will be a capital crime.

Won't someone think of the children?
 

Online Richard Crowley

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #58 on: January 08, 2016, 01:25:32 am »
Well you still know if the operator at the other end has valve audio preamp even if you have a solid state receiver.
Similarly an old 50’s SW valve radio is the best audio for HF I’ve yet heard.
That is just audiophoolery.

The only reason firebottles are still allowed is because there are so few of them left compared to incandescent lights which are quickly going illegal across most of the populated parts of the planet.
 

Offline jolshefsky

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #59 on: January 08, 2016, 02:08:07 am »
Hope you are joking.. Glass cups are not electronic devices. There is NOT a safety regulation for them...

Alas, very noisy people love the idea of an unregulated world. They think everyone's life and health is disposable, especially the stupid. They think that they are so smart as to avoid all danger. They don't realize that young children are incredibly ignorant (and will hopefully be able to grow out of it someday). They don't realize that there are ordinary lapses in attention or awareness that, rather than causing a permanent disability, could simply be met with an "oops" if there were some protection in place.

So rather than assessing whether a danger is a necessary part of the object (e.g. knives need to have sharp edges) or whether it is just cheap, lazy design (e.g. not putting a guard around a rotating fan), their knee-jerk libertarian reaction is to declare that all suggestions to insist on design that is rooted in human behavior (and error) are worse than worthless, coddling the incompetent.
May your deeds return to you tenfold.
 

Offline krivx

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #60 on: January 08, 2016, 02:34:48 am »
Small-bottle tubes tend to run about 50C at the glass. This would make them quite a bit less of a danger than a household radiator.
 

Online blueskull

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #61 on: January 08, 2016, 03:19:05 am »
Alas, very noisy people love the idea of an unregulated world. They think everyone's life and health is disposable, especially the stupid. They think that they are so smart as to avoid all danger. They don't realize that young children are incredibly ignorant (and will hopefully be able to grow out of it someday). They don't realize that there are ordinary lapses in attention or awareness that, rather than causing a permanent disability, could simply be met with an "oops" if there were some protection in place.

Natural selection will have to do its job. Kids shall not be allowed to touch hot things, even if they touched a hot thing, reflection will throw their hand away.
If some kid got burned by warm glass, and he decided to keep their hand on to see if it will cook his hand thoroughly, then he should be hurt for the sake of stupidity.
For the exact reason, there are kid safe furniture and more similar products, which by my standard, a force stopping human race from evolving.
If one kid just failed to learn anything even after got hurt, he should get more hurt. If his parent failed to teach him basic safety, they should be imprisoned.

Hurts done --> not a big deal --> lessons learned --> mentally evolved.
                  --> caused serious injury --> can not find a spouse --> genetically extincted --> statistically human race evolved.

The modern society that focuses on let everyone live safely and have their gene preserved is on the direct opposite of human evolving.
 

Offline Pentium100

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #62 on: January 08, 2016, 03:33:52 am »
I built my tube amp without the shield. I actually told somebody that it was OK if he wanted to touch the tubes while the amp was on, it's just that parts of the glass were about 150C.

Small tubes do not get hot enough to burn a hand when touched, unless they are used at the maximum plate dissipation the ratings allow. Power tubes do get quite hot, especially in class A amplifiers.

Alas, very noisy people love the idea of an unregulated world. They think everyone's life and health is disposable, especially the stupid. They think that they are so smart as to avoid all danger. They don't realize that young children are incredibly ignorant (and will hopefully be able to grow out of it someday). They don't realize that there are ordinary lapses in attention or awareness that, rather than causing a permanent disability, could simply be met with an "oops" if there were some protection in place.

There is a need for some common sense, especially if the danger is not all that great. Let's say somebody does touch the 150C tube or pick up a soldering iron on the wrong end. At most, they will get some small burn (unlike spilling hot oil on your hand, touching something hot usually invokes the reflex of taking the hand away and that stops the damage), it may be painful, but not lethal or permanent. I however, will insulate live mains wires so the cannot be touched even if I am connecting them temporarily (for a few minutes) or I will use an insulating transformer because touching a live wire can kill.

Incandescent lightbulbs get hot too, and table lamps usually do not have protection from touch. How did the human race not go extinct because it was possible to touch a hot lightbulb?

We should not have instructions that tell not to put a cat in a microwave oven (or a regular over for that matter) and we should not reward the people that do it even though the instructions did not forbid it. Some things should be understood by all and parents should teach those things to their children. If they don't do that, then maybe those genes should have a reduced chance of reproducing...

Lets say you have a sauna. You can pour water on the hot stones to increase the humidity. Do you really need an instruction to tell you that 1) stones are hot, do not touch them and 2) do not pour gasoline on them?
 

Online Brumby

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #63 on: January 08, 2016, 03:44:55 am »
Lets say you have a sauna. You can pour water on the hot stones to increase the humidity. Do you really need an instruction to tell you that 1) stones are hot, do not touch them and 2) do not pour gasoline on them?

You never know......
 

Offline G7PSK

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #64 on: January 08, 2016, 03:49:53 am »
I built my tube amp without the shield. I actually told somebody that it was OK if he wanted to touch the tubes while the amp was on, it's just that parts of the glass were about 150C.



Obviously not valves with a top hat anode connection at 750 Volts then.
 

Offline station240

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #65 on: January 08, 2016, 04:06:45 am »
Heh, I remember when Silicon Chip finally after years of complaints finally made something with a valve pre-amp in it.
They deliberately over drove the input signal to the valve, so it flattered the top of the curve, for that 'choob' sound.

This on the other hand has a unity gain of 1, don't think the Chinese understand what valve amps are really about. Could be interesting to modify this in various ways, eg more gain, higher voltage HT, changed input/output levels. Perhaps it's next owner could consider this.

I think we are all missing the point here. This was sold for about 50 bucks. No true "audiophile" would buy a 50 dollar headphone amp, so this is not "audiophile quality".

Now, if you would sell the same thing for 500 dollars, it would be a different story...

You mean once you add the cloth power cord, oak plinth and gold plated sockets. Oh and replace the blue LEDs with orange ones.
Actually it would be an interesting experiment to do that, put it up on ebay, and see what idiot buys it.
 

Offline xygor

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #66 on: January 08, 2016, 04:57:30 am »
The grid is positive wrt the cathode!?

It's running in enhancement mode (to borrow a mosfet term).  The data sheet gives data for depletion mode.  I suppose that's a consequence of running the plate voltage so low.  It's not a mode that's characterized on the data sheet.  What do the curves look like for this mode?  A spice model probably couldn't be trusted to give the correct result for this region of operation.
 

Offline Salas

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #67 on: January 08, 2016, 05:04:46 am »
How high is the anode voltage used and how is it created in this headphones amp?

About 24v total (-12 on cathode, +12 on anode) and two small switching regulators are used to create the voltage rails.

Thanks. There seems to be a small usable area for the 6J9 in such low B+ but in grid current territory.
Hence the input coupling capacitors I suppose.

 

Offline Salas

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #68 on: January 08, 2016, 05:16:03 am »
The grid is positive wrt the cathode!?

It's running in enhancement mode (to borrow a mosfet term).  The data sheet gives data for depletion mode.  I suppose that's a consequence of running the plate voltage so low.  It's not a mode that's characterized on the data sheet.  What do the curves look like for this mode?  A spice model probably couldn't be trusted to give the correct result for this region of operation.

Look here http://klausmobile.narod.ru/testerfiles/6j9pe.htm
 

Offline N2IXK

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #69 on: January 08, 2016, 05:33:21 am »

Obviously not valves with a top hat anode connection at 750 Volts then.

Ampeg introduced their famous SVT series amplifiers using 6146 tubes (which have plate caps), but quickly shifted to 6550 tubes without the caps.  Users getting zapped when changing tubes was at least part of the reason behind the change.
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Offline timb

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EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #70 on: January 08, 2016, 05:35:12 am »
Hope you are joking.. Glass cups are not electronic devices. There is NOT a safety regulation for them...

Alas, very noisy people love the idea of an unregulated world. They think everyone's life and health is disposable, especially the stupid. They think that they are so smart as to avoid all danger. They don't realize that young children are incredibly ignorant (and will hopefully be able to grow out of it someday). They don't realize that there are ordinary lapses in attention or awareness that, rather than causing a permanent disability, could simply be met with an "oops" if there were some protection in place.

So rather than assessing whether a danger is a necessary part of the object (e.g. knives need to have sharp edges) or whether it is just cheap, lazy design (e.g. not putting a guard around a rotating fan), their knee-jerk libertarian reaction is to declare that all suggestions to insist on design that is rooted in human behavior (and error) are worse than worthless, coddling the incompetent.

The sad reality is that the majority of people's lives *are* disposable. People want to think every life is sacred and everybody is a unique special snowflake. They're not.

There's billions of people alive on this pale blue dot, if any one of them disappeared tomorrow, 99.999999...% of the rest wouldn't notice or care. It happens every day.

If every life *was* sacred then the money and time first world countries (whose quality of life and mortality rates are pretty damn good) spent on THINK OF THE CHILDREN causes would instead go to *actual* children who are drinking filthy water and starving to death in third world shit holes, the world might be a better place.

But it's not. Instead, it goes to making sure little Johnny doesn't suffer the physical and emotional trauma of getting a boo-boo. Proving that people are greedy, selfish and value some lives more than others.


Sent from my Smartphone
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Offline retrolefty

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #71 on: January 08, 2016, 06:04:59 am »
Hope you are joking.. Glass cups are not electronic devices. There is NOT a safety regulation for them...

Alas, very noisy people love the idea of an unregulated world. They think everyone's life and health is disposable, especially the stupid. They think that they are so smart as to avoid all danger. They don't realize that young children are incredibly ignorant (and will hopefully be able to grow out of it someday). They don't realize that there are ordinary lapses in attention or awareness that, rather than causing a permanent disability, could simply be met with an "oops" if there were some protection in place.

So rather than assessing whether a danger is a necessary part of the object (e.g. knives need to have sharp edges) or whether it is just cheap, lazy design (e.g. not putting a guard around a rotating fan), their knee-jerk libertarian reaction is to declare that all suggestions to insist on design that is rooted in human behavior (and error) are worse than worthless, coddling the incompetent.

The sad reality is that the majority of people's lives *are* disposable. People want to think every life is sacred and everybody is a unique special snowflake. They're not.

There's billions of people alive on this pale blue dot, if any one of them disappeared tomorrow, 99.999999...% of the rest wouldn't notice or care. It happens every day.

If every life *was* sacred then the money and time first world countries (whose quality of life and mortality rates are pretty damn good) spent on THINK OF THE CHILDREN causes would instead go to *actual* children who are drinking filthy water and starving to death in third world shit holes, the world might be a better place.

But it's not. Instead, it goes to making sure little Johnny doesn't suffer the physical and emotional trauma of getting a boo-boo. Proving that people are greedy, selfish and value some lives more than others.


Sent from my Smartphone

THINK OF THE CHILDREN

 When people, organizations, political parties, religions, etc use that term they don't mean all the children, just theirs and the immediate group or area they most closely associate with. That is not concern for all children of all areas of the world and with all religious or non-religious groups.

 It's not unlike the NIMBY syndrome which also shows up just as frequently. People will almost always first apply their own self-interests whatever they are, which is also the underlining foundation of a capitalistic world, which has so far proven to be the most successful system yet developed. Maybe someday the outer space Aliens will arrive and impose a better system on all of us that is 'more fair and 'equal outcomes' for everyone. However it that happens I'm sure we will find faults with the Aliens system of government.  ;)
 
 

Offline xygor

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #72 on: January 08, 2016, 06:08:06 am »
The grid is positive wrt the cathode!?

It's running in enhancement mode (to borrow a mosfet term).  The data sheet gives data for depletion mode.  I suppose that's a consequence of running the plate voltage so low.  It's not a mode that's characterized on the data sheet.  What do the curves look like for this mode?  A spice model probably couldn't be trusted to give the correct result for this region of operation.

Look here http://klausmobile.narod.ru/testerfiles/6j9pe.htm
What's the difference in meaning of "Grid" and "Grid Drive" in the voltmeter section? Is this the voltage across a grid current sense resistor?

A modern tube tester.  Cool!
 

Offline retrolefty

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #73 on: January 08, 2016, 06:12:34 am »
The grid is positive wrt the cathode!?

It's running in enhancement mode (to borrow a mosfet term).  The data sheet gives data for depletion mode.  I suppose that's a consequence of running the plate voltage so low.  It's not a mode that's characterized on the data sheet.  What do the curves look like for this mode?  A spice model probably couldn't be trusted to give the correct result for this region of operation.

Look here http://klausmobile.narod.ru/testerfiles/6j9pe.htm
What's the difference in meaning of "Grid" and "Grid Drive" in the voltmeter section? Is this the voltage across a grid current sense resistor?

A modern tube tester.  Cool!

 A grid is a physical thing, conductive circular mesh surface placed between the cathode and anode of a tube. Grid drive is a voltage (AC + any required DC bias value) that will effect/control the current conduction between the anode and cathode terminals.
 

Offline xygor

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #74 on: January 08, 2016, 06:19:07 am »

 A grid is a physical thing, conductive circular mesh surface placed between the cathode and anode of a tube. Grid drive is a voltage (AC + any required DC bias value) that will effect/control the current conduction between the anode and cathode terminals.


Let me rephrase: Grid Voltage and Grid Drive Voltage.  It's specific to the tube tester.
Edit: Salas' tube tester.
« Last Edit: January 08, 2016, 06:31:20 am by xygor »
 

Offline xygor

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #75 on: January 08, 2016, 06:21:28 am »
Remove the tube and the cathode resistor.  Short the grid connection to the cathode connection at the tube socket.  Voilà!
Edit: spelling.
« Last Edit: January 08, 2016, 06:27:43 am by xygor »
 

Offline Sylvain

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #76 on: January 08, 2016, 06:54:18 am »
Really interesting ...
I didn't know anything about valve tubes before watching this video.  :-+

One question that poped up in my mind : could the "quality" of the 6V supply affect the quality of the sound by modifying the power of heating element (and thus the electron flow) ?

« Last Edit: January 08, 2016, 06:57:38 am by Sylvain »
 

Online Richard Crowley

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #77 on: January 08, 2016, 07:01:40 am »
One question that pops up in my mind : could the "quality" of the 6V supply affect the quality of the sound by modifying the power of heating element (and thus the electron flow) ?

In some primitive (or high-power) tubes, the heater is also the cathode. But for almost all tubes used for audio, the cathode is a metal tube/oval with the heater filament wires INSIDE for indirect heating.  So the actual current through the heater isn't really "in the circuit". Most tube heaters were operated directly from mains-frequency (50/60Hz) AC power.  The thermal mass of the heater completely swamps out any effect from the sine-wave power of the heater current waveform. In exactly the same way that nobody can actually perceive "flicker" from an incandescent lamp operating at mains frequency.

Of course if circuit design or execution is sloppy, (or component failure) it is possible for the heater AC "hum" to get into the signal path. But that is an exceptional condition and not commonly found in properly designed circuits.

"Golden ears" audiophools imagine they can "hear" the difference between AC and DC power in an indirectly-heated filament tube. But they imagine lots of other things also, so that comes as no particular surprise.
 

Offline krivx

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #78 on: January 08, 2016, 07:09:43 am »
One question that pops up in my mind : could the "quality" of the 6V supply affect the quality of the sound by modifying the power of heating element (and thus the electron flow) ?

In some primitive (or high-power) tubes, the heater is also the cathode. But for almost all tubes used for audio, the cathode is a metal tube/oval with the heater filament wires INSIDE for indirect heating.  So the actual current through the heater isn't really "in the circuit". Most tube heaters were operated directly from mains-frequency (50/60Hz) AC power.  The thermal mass of the heater completely swamps out any effect from the sine-wave power of the heater current waveform. In exactly the same way that nobody can actually perceive "flicker" from an incandescent lamp operating at mains frequency.

Of course if circuit design or execution is sloppy, (or component failure) it is possible for the heater AC "hum" to get into the signal path. But that is an exceptional condition and not commonly found in properly designed circuits.

"Golden ears" audiophools imagine they can "hear" the difference between AC and DC power in an indirectly-heated filament tube. But they imagine lots of other things also, so that comes as no particular surprise.


People building high-gain (high distortion) guitar amplifiers have reported that power the heater of the first tube with DC can cut down on hum that is otherwise inductively coupled through the heater wiring. It shouldn't do much in linear amplifiers. Apparently noisy DC on heaters can result in signal noise as well, surprisingly enough.
 

Offline Pentium100

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #79 on: January 08, 2016, 07:14:08 am »
Obviously not valves with a top hat anode connection at 750 Volts then.
No. I also do not particularly like the higher voltages, you know, when the wires have to be a certain distance apart or they would arc over. I have seen insulated top connectors, those would reduce the chance of getting zapped.

"Golden ears" audiophools imagine they can "hear" the difference between AC and DC power in an indirectly-heated filament tube. But they imagine lots of other things also, so that comes as no particular surprise.

Depending on the tube and the circuit design, in some cases a small current can flow between the cathode and heater, introducing hum. Of course this is only noticeable in something like a phono preamp where the input signal is a couple of mV. After all, pretty much all tubes were used with AC powered heater. Only battery operated devices had DC heaters (and most tubes designed for battery operation were directly heated) back in the day when tubes were common.
 

Offline rrinker

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #80 on: January 08, 2016, 07:17:56 am »
 It was common for small 6.3V transformers to be called "filament transformers". Guess why. Younger players may rarely if ever come across that term.

 

Offline N2IXK

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #81 on: January 08, 2016, 07:20:43 am »
People building high-gain (high distortion) guitar amplifiers have reported that power the heater of the first tube with DC can cut down on hum that is otherwise inductively coupled through the heater wiring. It shouldn't do much in linear amplifiers. Apparently noisy DC on heaters can result in signal noise as well, surprisingly enough.

The usual heater construction is a folded wire inserted inside the cathode sleeve.  In tubes specifically designed for low level audio preamp applications, a twisted/coiled heater wire was used to help cancel out the electromagnetic field that could couple into the cathode circuit and result in hum. An example is the 7025, which is a 12AX7 with a coiled heater, specifically designed for audio applications.

Another trick was to use the input stage heaters as cathode resistors for the push-pull output stage. In this way, they were operated on DC current, without the expense of additional transformer windings/rectifiers/filter caps.
« Last Edit: January 08, 2016, 07:22:39 am by N2IXK »
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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #82 on: January 08, 2016, 07:39:07 am »

 A grid is a physical thing, conductive circular mesh surface placed between the cathode and anode of a tube. Grid drive is a voltage (AC + any required DC bias value) that will effect/control the current conduction between the anode and cathode terminals.


Let me rephrase: Grid Voltage and Grid Drive Voltage.  It's specific to the tube tester.
Edit: Salas' tube tester.

Its not my tester, I just have a TV7 mutual conductance military tester, when the Klausmobile is a Russian curve tracer project that I don't think it ever went commercial

http://www.klausmobile.narod.ru/projects/pr_02_kmtt_e.htm
A famous digital one was the Italian Audiomatica Sofia (great-expensive-obsolete) from the same guys that make the Clio electro-acoustic measurement system

The most accessible tracer today maybe is the µTracer 3+ kit

http://www.dos4ever.com/uTracer3/uTracer3_pag0.html




 

Offline Salas

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #83 on: January 08, 2016, 08:11:08 am »
The grid is positive wrt the cathode!?

It's running in enhancement mode (to borrow a mosfet term).  The data sheet gives data for depletion mode.  I suppose that's a consequence of running the plate voltage so low.  It's not a mode that's characterized on the data sheet.  What do the curves look like for this mode?  A spice model probably couldn't be trusted to give the correct result for this region of operation.

Look here http://klausmobile.narod.ru/testerfiles/6j9pe.htm
What's the difference in meaning of "Grid" and "Grid Drive" in the voltmeter section? Is this the voltage across a grid current sense resistor?

A modern tube tester.  Cool!

Could be a sense voltage yes. Grid drive is overdriving a valve by pushing it to grid current leaking territory with near zero and above zero voltage swing, but there is also capacitor blocking possibility when AC coupled. i.e. to peg on big transients until discharged. Nasty distortion effect. It takes a DC coupled buffer driver stage either valve or Mosfet to really push it. Especially for power tubes where it makes sense. In this one its just a starved tube drive necessity to go down there because of little anode voltage available. The guys who made this headphone gadget amp wanted to have tubes for show off or to just spice it up too, but it looks they knew how to work with valves even in weird modes nonetheless.
 

Offline jitter

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #84 on: January 08, 2016, 08:44:28 am »
Personally I prefer exact sound reproduction, not distorted, hence I use high end DAC coupled with monitor grade IEM.
What do you consider exact sound reproduction?

IMHO, there's absolutely nothing like the live sound of instruments (that are NOT electronically amplified in any way). How could a speaker, of which the membrane that must reproduce the sound is of a different shape than any instrument, ever come close to reproducing the sound faithfully? Oh, it does a good job at trying, but it doesn't come close to  the real thing.
 
I have a good hifi system that even audiophiles wouldn't frown upon, and I am satisfied with it, but there's nothing like a live acoustic instrument. Perhaps that's one of the reasons why I recently took up learning to play the guitar (but it's also got something to do with doing it yourself).
 

Offline TheGreatGooglyMoogly

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #85 on: January 08, 2016, 09:17:06 am »
Finally posting two questions...

One: the output stage has one amplifier driving another unity buffer, then paralleling the outputs. Does this not introduce distortion or other issues due to the propagation delay of the NE5532? I know it has a global feedback, but seems like it would still have issues. A better solution would seem to parallel both amplifiers? Maybe I'm wrong - not an expert on audio buffers, but want to become one.

Two: I have read numerous times never to use SMT ceramic capacitors in audio paths since they 'microphone' and distort the signal. Is this the case or no?

Bonus rant... I HATE HATE HATE blue LEDs under tubes. Looks lame and doesn't let the pretty 'natural' glow out. If anything put an amber one in. Blah!  |O
 

Offline N2IXK

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #86 on: January 08, 2016, 09:28:02 am »
In high quality audio gear, ceramic caps (not just SMT ones) are generally frowned upon as coupling capacitors because they exhibit a change in capacitance with applied voltage due to the piezoelectric effect. Some are worse than others, however.
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Offline xygor

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #87 on: January 08, 2016, 09:33:04 am »
Two: I have read numerous times never to use SMT ceramic capacitors in audio paths since they 'microphone' and distort the signal. Is this the case or no?

It depends.  Class 1 (NPO, C0G, U2J,etc.) are pretty good.
Class 2 (X7R, Y5R, Z5U, etc.) can be pretty bad especially higher values in smaller packages.  If the signal has frequencies for which the capacitive reactance is much smaller than the impedance of the rest of the circuit, it's not too bad.  This would be the case for interstage coupling.  Otherwise the lower frequencies cause intermodulation distortion.  This would be likely be the case for filters and equalizers.
 

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #88 on: January 08, 2016, 09:53:52 am »
"Golden ears" audiophools imagine they can "hear" the difference between AC and DC power in an indirectly-heated filament tube. But they imagine lots of other things also, so that comes as no particular surprise.

I've heard that is you hook up the filament backward the audiophiles can hear Paul McCartney whispering to them.
 

Offline Groucho2005

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #89 on: January 08, 2016, 10:03:12 am »
One: the output stage has one amplifier driving another unity buffer, then paralleling the outputs. Does this not introduce distortion or other issues due to the propagation delay of the NE5532?
Probably insignificant for audio frequencies. Anyway, the bias of the tube (12V anode-cathode voltage, 2.5 mA cathode current) is so atrocious that the distortion of that "buffer" will dominate everything (which is of course by design). It's not unlike operating a BJT in it's saturation area which is ridiculous for a linear amplifier.

Tubes have a reputation of having high distortion which is not true if the circuit is designed properly.

If anyone is interested, here is an article on designing a tube audio buffer without any snakeoil and audiophoolery by Stuart Yaniger:
http://syclotron.com/?page_id=2380
« Last Edit: January 08, 2016, 10:07:59 am by Groucho2005 »
 

Online blueskull

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #90 on: January 08, 2016, 10:07:43 am »
"Golden ears" audiophools imagine they can "hear" the difference between AC and DC power in an indirectly-heated filament tube. But they imagine lots of other things also, so that comes as no particular surprise.

I've heard that is you hook up the filament backward the audiophiles can hear Paul McCartney whispering to them.

For those direct heated (filament is cathode) tubes, if not designed properly, you will hear hum.

DC filament has better tolerance to improper design regarding to hum.
 

Offline f4eru

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #91 on: January 08, 2016, 10:21:13 am »
No true "audiophile" would buy a 50 dollar headphone amp, so this is not "audiophile quality".
In china, 50 dollars are like 500 dollars :)

Tell the same people that it has SMPSs in there, and it'll fall off it's pedestal in the blink of an eye.
That's the reason of rubbing off the ICs : people not recognizing that this is a SMPS would not be able to search the ICs :)
 

Offline TheGreatGooglyMoogly

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #92 on: January 08, 2016, 10:35:30 am »
Two: I have read numerous times never to use SMT ceramic capacitors in audio paths since they 'microphone' and distort the signal. Is this the case or no?

It depends.  Class 1 (NPO, C0G, U2J,etc.) are pretty good.
Class 2 (X7R, Y5R, Z5U, etc.) can be pretty bad especially higher values in smaller packages.  If the signal has frequencies for which the capacitive reactance is much smaller than the impedance of the rest of the circuit, it's not too bad.  This would be the case for interstage coupling.  Otherwise the lower frequencies cause intermodulation distortion.  This would be likely be the case for filters and equalizers.

I'll bet literal bottom dollar that they are Y5V. Maybe X5R, but larger than 0.1uF C0G are virtually non-existent and very expensive (have used a 0.1uF C0G before).
 

Online Richard Crowley

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #93 on: January 08, 2016, 10:41:15 am »
This will all be moot soon. Apple is dropping the 3.5mm analog output jack completely.
If you don't want to use wireless (Bluetooth) headphones, there will be digital headphones that plug into the Lightning connector.
No word on how you will plug in BOTH you headphones AND your charger, sync cable, etc.
Not letting the audio loose in the analog domain means they can enforce DRM right to your eardrums.
 

Offline retrolefty

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #94 on: January 08, 2016, 10:46:59 am »
This will all be moot soon. Apple is dropping the 3.5mm analog output jack completely.
If you don't want to use wireless (Bluetooth) headphones, there will be digital headphones that plug into the Lightning connector.
No word on how you will plug in BOTH you headphones AND your charger, sync cable, etc.
Not letting the audio loose in the analog domain means they can enforce DRM right to your eardrums.

 Wow is that for real? So in the near future the Apple user can't pipe his/her music to a typical analog audio amp/speaker system via a analog jack unless it's an approved and compatible amplifier?

 Don't own anything Apple, so no problem here.  :--
 


Online Fungus

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #96 on: January 08, 2016, 11:53:35 am »
Quote
the iPhone 7 will be too thin to include a standard 3.5-millimeter headphone jack...

But will it bend?
 

Online blueskull

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #97 on: January 08, 2016, 12:55:13 pm »
Quote
the iPhone 7 will be too thin to include a standard 3.5-millimeter headphone jack...

But will it bend?

Bent CEO makes bent phones -- there is nothing wrong there.

Legal disclaimer: this post is only intended to entertain people with its pun, the author does not express any discrimination against BLGT.
 

Offline rrinker

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #98 on: January 08, 2016, 01:06:00 pm »
"Golden ears" audiophools imagine they can "hear" the difference between AC and DC power in an indirectly-heated filament tube. But they imagine lots of other things also, so that comes as no particular surprise.

I've heard that is you hook up the filament backward the audiophiles can hear Paul McCartney whispering to them.

 Who are you kidding, everyone knows Paul's dead, they told us that many many moons ago.

Or maybe his ghost lives amongst the vacuum in the valves.

 

Offline gadget73

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #99 on: January 08, 2016, 01:58:17 pm »

The usual heater construction is a folded wire inserted inside the cathode sleeve.  In tubes specifically designed for low level audio preamp applications, a twisted/coiled heater wire was used to help cancel out the electromagnetic field that could couple into the cathode circuit and result in hum. An example is the 7025, which is a 12AX7 with a coiled heater, specifically designed for audio applications.

Another trick was to use the input stage heaters as cathode resistors for the push-pull output stage. In this way, they were operated on DC current, without the expense of additional transformer windings/rectifiers/filter caps.

This is always a cute trick.  I have a Fisher TA-600 that uses this system.  One of the phono tubes developed a heater-cathode short, and that particular cathode was grounded.  It did some unhappy things to the bias on the output stage. 

There are certainly some interesting bits of economy used on electronics at times.  One of the oddest I've seen on a tube amp was the original bias supply in my big Bogen PA amps.  It used a 0.47 uf cap off the 300 VAC winding to feed through a diode to get the negative DC supply.   That now has a small 6vac transformer fed backwards to run the bias supply.

Tube amps have long been a contentious thing in the electronics world.  Audio guys tell you they sound better.  Measurement devices tell you they are shite on a stick.  Personally I say they are both true.  Tube amps measure badly but are pleasing to listen to.   Its the difference between steam power and internal combustion engines.  By every measurable way the IC engine wins, but we still like steam trains.   
 

Offline gadget73

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #100 on: January 08, 2016, 02:16:03 pm »

I discovered a long time ago it makes no difference which way the little packets of energy go, it all works out just fine. :)

Also just too many parts to keep track of :) 

24v K-A and a cathode follower arrangement?  Whats the point?  It would give lower output impedance, but feeding into an op-amp its not like that would be required. Not enough voltage to make any useful gain anyway.  Wonder how far out of the linear operating range it is.
In my opinion there is no point, That is not a good tube for a cathode follower, the designer is not taking advantage of the high input impedance a vacuum tube offers, and as you pointed out the plate voltage (B+) is too low.

The designer isn't even trying to prove something.

Why not?
build a 30W headphone amplifier using all tubes, no output transformer, using an output differential amplifier with cathode output. (to keep the voltage and impedance low)? Run it on say............125V regulated(+/- 65.5V).

That would be a concept amplifier worth building, if for no other reason than to prove the idea. :)

 Why 30 watts, not many headphones can accept even peaks at that level? About the only thing that might differentiate a 'headphone amp' form other audio amps is that it might be designed to only work at the higher output impedance of most headsets.

Not many headphones can accept 30W RMS, but 30W peaks? Sure.

I do not suspect that your ears would though.  It takes such a tiny amount of power to run a set of cans that even a watt of power would give you ample dynamic range for anything you want to listen to, even at levels that would make your ears bleed.  There are a few designs out there for straight cathode drive can amps with low tube count.  A 6AS7 works nicely for OTL headphone amp duty.
 

Offline Pentium100

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #101 on: January 08, 2016, 03:08:00 pm »
I have a headphone amp with a white cathode follower made from ECC88s (voltage gain stage is another ECC88). Works quite well, even with 32ohm headphones. Though I currently use 300ohm headphones (did not specifically search for the high impedance).

As for why I need a headphone amp - not all devices I have provide a headphone output and I did not want to use a speaker amp for the headphones all the time (too easy to accidentally turn on the speakers in the middle of the night).
 

Offline jitter

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #102 on: January 08, 2016, 05:58:57 pm »
"Golden ears" audiophools imagine they can "hear" the difference between AC and DC power in an indirectly-heated filament tube. But they imagine lots of other things also, so that comes as no particular surprise.

I've heard that is you hook up the filament backward the audiophiles can hear Paul McCartney whispering to them.

 :-DD

I thought he was dead... we're supposed to be stuck with Faul now...  ;)
 

Offline boffin

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #103 on: January 08, 2016, 07:04:39 pm »
Wow is that for real? So in the near future the Apple user can't pipe his/her music to a typical analog audio amp/speaker system via a analog jack unless it's an approved and compatible amplifier?

It's more annoying
http://www.patentlyapple.com/patently-apple/2015/09/apple-granted-an-alternative-headset-connector-patent-that-may-never-see-the-light-of-day.html
An Apple headphone plug that will/might work in other devices, but not other devices into an Apple device, unless you pay their patent licensing fee.

Boffin at play https://snafu.ca/
 

Offline timb

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EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #104 on: January 08, 2016, 07:13:04 pm »
Just because they're removing the 3.5mm jack, doesn't mean it won't still output analog audio. They could very well push the analog audio over a couple of pins on the Lightning connector. The older 30-pin connectors did that. You would then use a simple Lightning to 3.5mm adapter.

If they don't do analog transport over the Lightning port, they'd be to just stick a DAC in the adapter.

Or they won't remove it from the phone at all. 99% of Apple rumors are wrong, so perhaps it's best not to spread FUD just yet. Also, Apple patents *a ton* of stuff. Of that, a small number makes it into production.

Either way, you'll still be able to use headphones, I guarantee that. It's sort of a basic requirement.
Any sufficiently advanced technology is indistinguishable from magic; e.g., Cheez Whiz, Hot Dogs and RF.
 

Offline AF6LJ

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #105 on: January 09, 2016, 02:48:00 am »
Just because they're removing the 3.5mm jack, doesn't mean it won't still output analog audio. They could very well push the analog audio over a couple of pins on the Lightning connector. The older 30-pin connectors did that. You would then use a simple Lightning to 3.5mm adapter.

If they don't do analog transport over the Lightning port, they'd be to just stick a DAC in the adapter.

Or they won't remove it from the phone at all. 99% of Apple rumors are wrong, so perhaps it's best not to spread FUD just yet. Also, Apple patents *a ton* of stuff. Of that, a small number makes it into production.

Either way, you'll still be able to use headphones, I guarantee that. It's sort of a basic requirement.

There is a trend to remove the analogue link to the outside world, the copyright people want to make it hard to plug that phone  (or whatever) into a recording device. They think we are all criminals and want to share our music with the world.
Sue AF6LJ
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Offline Oskar

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #106 on: January 09, 2016, 03:22:01 am »
That's funny that the tube is just a buffer.  Thanks for using the DS1054Z and highlighting the channel control issue.  That does not take the DS1054Z off my to purchase list. 
Nice video.
 

Online Fungus

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #107 on: January 09, 2016, 05:16:19 am »
That's funny that the tube is just a buffer.

Not just a buffer, the electric heater in the tube will add 'warmth' to the electrons.

What audiophile doesn't want warmed-up sound?
 

Online Richard Crowley

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #108 on: January 09, 2016, 05:58:03 am »
Either way, you'll still be able to use headphones, I guarantee that. It's sort of a basic requirement.
Sure. Apple headphones (or Apple-licenced headphones) at an inflated Apple price.
It's plays nicely into their "Walled Garden" scheme where they control EVERYTHING including the customer.
I am extraordinarily dubious about this.
 

Online Fungus

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #109 on: January 09, 2016, 06:04:34 am »
Either way, you'll still be able to use headphones, I guarantee that. It's sort of a basic requirement.
Sure. Apple headphones (or Apple-licenced headphones) at an inflated Apple price.
It's plays nicely into their "Walled Garden" scheme where they control EVERYTHING including the customer.
I am extraordinarily dubious about this.

Nah, there's no conspiracy.

It's a phone. The whole point is that it's wireless and the music plays remotely while you select songs on the screen. Bluetooth sound is built into everything these days. You don't connect a cable when you listen to your iPhone in your car, why should you do it at home.

It's the way the iTunes generation rolls, Apple is just going along.
 

Offline jdamewood

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #110 on: January 09, 2016, 05:28:59 pm »
Drawing an  analogy to a J-FET is simply wrong.
A more apt analogy would be a MOS-FET since there is an insulator between the elements like in a vacuum tube.


Sorry Dave Ya got it wrong.

No I think you got it wrong, if the control grid voltage would become positive a grid current would flow, just like in a J-FET.

Then the cathode follower would be 180° out of phase from input signal.

Preemptive call to myself as being wrong, if needed.
 

Offline Pentium100

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #111 on: January 09, 2016, 06:15:45 pm »
Then the cathode follower would be 180° out of phase from input signal.

Preemptive call to myself as being wrong, if needed.

The cathode follower output is in phase with the input. When the control grid voltage becomes more positive than it was at idle, more current flows trough the tube causing higher voltage drop on the cathode resistor. If the control grid voltage becomes positive with respect to cathode, then some grid current flows, but the plate current is increased even more.

I have attached the IV curves of a Russian 6?2? (6N2P) tube, which is similar to 12AX7. It shows the effect of a positive grid voltage.
« Last Edit: January 09, 2016, 06:21:39 pm by Pentium100 »
 

Offline gildasd

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #112 on: January 10, 2016, 06:18:13 am »
Either way, you'll still be able to use headphones, I guarantee that. It's sort of a basic requirement.
Sure. Apple headphones (or Apple-licenced headphones) at an inflated Apple price.
It's plays nicely into their "Walled Garden" scheme where they control EVERYTHING including the customer.
I am extraordinarily dubious about this.
The day Apple removes the 3.5 is the day I buy a Samsung...
Apple in ear head speakers are nice, but in my use, worn under noise protection ear muffs, they last only a few weeks before splitting open.
Cheap PVC based models last until the conductors split.
I like Apple products, but my brand loyalty breaks down when said brand tries to shag me, in a fashion frowned by the ecclesiastical hierarchy, without so much as the courtesy of a reach around.
I'm electronically illiterate
 

Offline gadget73

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #113 on: January 10, 2016, 03:28:32 pm »

Then the cathode follower would be 180° out of phase from input signal.

Preemptive call to myself as being wrong, if needed.

Cathode followers are in-phase with the input signal, anode follower would be 180 out of phase.   
 

Offline 13hm13

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #114 on: January 10, 2016, 06:27:03 pm »
Drawing an  analogy to a J-FET is simply wrong.
A more apt analogy would be a MOS-FET since there is an insulator between the elements like in a vacuum tube.


Sorry Dave Ya got it wrong.
I think Dave meant in a GENERIC way: tubes and FETs are voltage amps (not current).
 

Offline jitter

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #115 on: January 10, 2016, 06:35:10 pm »
The way I understood the analogy is electrons flowing through a vacuum are being effected by the electrical fields on the grids. Hence the analogy to the FE part of a FET.
 

Offline AF6LJ

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #116 on: January 11, 2016, 12:52:08 am »
Drawing an  analogy to a J-FET is simply wrong.
A more apt analogy would be a MOS-FET since there is an insulator between the elements like in a vacuum tube.


Sorry Dave Ya got it wrong.
I think Dave meant in a GENERIC way: tubes and FETs are voltage amps (not current).

That's true The J-FET analogy just doesn't work.
:)
Sue AF6LJ
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Online Brumby

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #117 on: January 11, 2016, 01:07:05 pm »
Drawing an  analogy to a J-FET is simply wrong.
A more apt analogy would be a MOS-FET since there is an insulator between the elements like in a vacuum tube.


Sorry Dave Ya got it wrong.
I think Dave meant in a GENERIC way: tubes and FETs are voltage amps (not current).

+1

After all, it's a tear-down style examination, not a quantum physics analysis.
 

Offline rch

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #118 on: January 11, 2016, 10:33:35 pm »
+1.   To those of us brought up on valves, JFETs are just like valves, and bipolar transistors are alien and odd!
 

Online Richard Crowley

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #119 on: January 13, 2016, 05:22:15 am »
From the BBC yesterday....

Quote
The 19th Century plug that's still being used

After rumours that Apple was going to get rid of the headphone jack in its imminent iPhone 7, more than 200,000 people have signed a petition asking them to reconsider. This humble plug is a rare example of technology that has stood the test of time, writes Chris Stokel-Walker.

For what remains an unconfirmed rumour, a lot of people are upset about the new iPhone. It's alleged that Apple will be scrapping the 3.5mm socket, instead leaving headphones to be plugged into the "Lightning" port - the company's own design of socket.

Cynics have pointed out that while this might enable iPhones to be slightly thinner, it will render many headphones useless and force manufacturers to pay Apple a fee to use their Lightning plugs on products.

The petition says Apple's purported move would "singlehandedly create mountains of electronic waste".

...history of the phone plug...

And yet, if the rumours - which Apple is not commenting on - are true, it bodes ill for the 3.5mm jack.

Apple has a track record of being early to abolish things which then start to disappear from rival products too. It killed the 3.5 inch floppy disk early. It also was among the first to remove optical drives.

But those signing the petition on the Sum of Us site and social media users have suggested that Apple's motive is greed.

The potential grief in a switch to Apple's proprietary Lightning connector is obvious.

"It feels painful because you've got hundreds of millions of devices out there that are using the old standard," says Horace Dediu, a technology analyst with in-depth knowledge of Apple.

If you're using £1,000 headphones with your iPhone at the moment, you're going to be slightly cross.

And Charlie Slee thinks consumers are also concerned about ceding control to Apple. "People are mainly upset because they like to think they're in control of their technology," he says.

But this sense of the consumer in control is misplaced, Slee says. "Actually, the contrary is true: The big technology companies have always been in control of how you listen to music and watch videos."

http://www.bbc.com/news/magazine-35253398

I don't agree that if Apple ditches the 3.5mm connector, it spells doom for that connector in the Rest Of the World.  But, at least as far as I am concerned, it just reinforces my distain for everything Apple.  If I were a dumb consumer appliance-operator, I would probably have a different opinion.
 

Online helius

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #120 on: January 13, 2016, 08:37:50 am »
I very much doubt the cross section of "£1,000 headphone users" who plug them into iphones is significant. Aren't all products in that range either 600 ohm, electrostatic, or otherwise not driveable from low-output equipment?
 

Offline rch

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #121 on: January 13, 2016, 10:01:19 am »
I very much doubt the cross section of "£1,000 headphone users" who plug them into iphones is significant. Aren't all products in that range either 600 ohm, electrostatic, or otherwise not driveable from low-output equipment?

Apple users may well be able to purchase £1000 headphones which look just like £3.50 headphones to the rest of us.

(DOI moderately keen Apple user.)
 

Offline timb

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EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #122 on: January 13, 2016, 10:15:53 am »
It's a rumor guys. It's either not going to happen, or if it does they will still be pumping analog out through the Lightning port, which will allow you to use a $5 passive adapter. I guarantee that.

It's pointless to get worked up over an Apple rumor. This particular one has been floating around since the iPhone 3GS. (This same rumor was about the iPhone 4 not having a headphone port.)

These get started one of three ways:

1) Some Apple Rumors Blog makes up some BS and tech sites pick it up as news.

2) Apple files a patent for "Method of transporting digital audio directly to headphones" and someone interprets that to mean the headphone port is being killed.

3) Someone at Apple says, "Gee wouldn't it be nice if we didn't have to deal with external ports, we could make phones that were paper thin!" This gets repeated like the Telephone Game and eventually someone posts it on Twitter as "Apple to remove headphone ports!"

In this case, it's likely a combination of all three. If anyone wants to start a pool on Apple removing the headphone port in the 7, I'll throw down $100 right now squarely in the Not Happening category.
Any sufficiently advanced technology is indistinguishable from magic; e.g., Cheez Whiz, Hot Dogs and RF.
 

Offline jitter

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #123 on: January 13, 2016, 05:33:42 pm »
Yeah, and that hyped rumor is talking about a 3.5 mm jack like that's the smallest jack there is... which it is not.
More than a decade ago I bought a HP PDA which already did away with the 3.5 mm jack and used a 2.5 mm jack instead. Thoughtfully HP supplied a 2.5 mm to 3.5 mm adapter...

So wether or not Apple stops using the 3.5 mm jack is really not that interesting, it's been hyped because it's Apple that (allegedly) does it. And even if they were to do it, I have no doubt that aftermarket converters would become available for very little money very quickly.
I hear people say: "Yeah but that costs extra..." Well, if you're prepared to buy overpriced stuff to begin with, a few more dollars/euros/whatever isn't going to hurt your wallet that much...  ;)
« Last Edit: January 13, 2016, 05:51:01 pm by jitter »
 

Offline gildasd

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #124 on: January 13, 2016, 09:37:52 pm »
Of the thing I find that Apple has to improve, thinness and size are not on my list.
Battery life, WIFI sensitivity and others come to mind.
In any case it goes in a rubber case...
I'm electronically illiterate
 

Online Fungus

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #125 on: January 14, 2016, 12:34:36 am »
More than a decade ago I bought a HP PDA which already did away with the 3.5 mm jack and used a 2.5 mm jack instead. Thoughtfully HP supplied a 2.5 mm to 3.5 mm adapter...

Apple will charge $20 for their legacy headphone compatibility system.

 

Offline krivx

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #126 on: January 14, 2016, 12:36:54 am »
More than a decade ago I bought a HP PDA which already did away with the 3.5 mm jack and used a 2.5 mm jack instead. Thoughtfully HP supplied a 2.5 mm to 3.5 mm adapter...

Apple will charge $20 for their legacy headphone compatibility system.

If it's an analog breakout cable then eBay will charge $3
 

Online Richard Crowley

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #127 on: January 14, 2016, 01:03:39 am »
Just because they're removing the 3.5mm jack, doesn't mean it won't still output analog audio. They could very well push the analog audio over a couple of pins on the Lightning connector.
Please explain how you think they could do that since there are no analog pins on the Lightning connector, and no re-assignable pins, either. 

And furthermore, the Lightning connector is not only proprietary, but contains active circuitry to ensure that ONLY Apple-provided (or Apple-licensed) gear can connect.  (Read: $$$)

Ref: https://en.wikipedia.org/wiki/Lightning_(connector)
 

Online Richard Crowley

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #128 on: January 14, 2016, 01:08:25 am »
Apple will charge $20 for their legacy headphone compatibility system.
If it's an analog breakout cable then eBay will charge $3
It cannot be an analog cable because Apples proprietary Lightning connector is digital-only.
Furthermore Lightning requires an active ID/authentication chip available only by licen$e from Apple.
That ensures that you won't be able to buy sensibly-priced accessories like simple cables, adapters, etc.
Apple must enforce their lucrative proprietary Walled Garden scheme.

Of course, the knock-off artists in Asia have proven themselves to be very clever.
So it seems within the realm of possibility that they can produce a counterfeit authentication chip.
Of course, then Apple could pull an FTDI stunt and brick all your counterfeit gear.
« Last Edit: January 14, 2016, 01:10:22 am by Richard Crowley »
 

Offline krivx

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #129 on: January 14, 2016, 01:31:09 am »
Apple will charge $20 for their legacy headphone compatibility system.
If it's an analog breakout cable then eBay will charge $3
It cannot be an analog cable because Apples proprietary Lightning connector is digital-only.
Furthermore Lightning requires an active ID/authentication chip available only by licen$e from Apple.
That ensures that you won't be able to buy sensibly-priced accessories like simple cables, adapters, etc.
Apple must enforce their lucrative proprietary Walled Garden scheme.

Of course, the knock-off artists in Asia have proven themselves to be very clever.
So it seems within the realm of possibility that they can produce a counterfeit authentication chip.
Of course, then Apple could pull an FTDI stunt and brick all your counterfeit gear.

The Wikipedia page posted above says that Apple sell a Lightning to 30pin (previous Ipod/IPhone connector) adapter and that it supports analog audio. Google brings up lots of knockoffs of this adapter, so maybe the work is already done?
 

Online Brumby

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #130 on: January 14, 2016, 01:35:37 am »
I would not be comfortable trusting Apple to give me what I want - and I certainly am not one of the 'faithful' that accepts whatever is served up as being the best option.

I like to think and decide for myself on a few things....
 

Online Fungus

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #131 on: January 14, 2016, 03:07:42 am »
Apple will charge $20 for their legacy headphone compatibility system.
If it's an analog breakout cable then eBay will charge $3
It cannot be an analog cable because Apples proprietary Lightning connector is digital-only.

Apple could just stick a new connector on the bottom with more pins.

It's not like they've never released an iPhone that was incompatible with previous-gen peripherals.
 

Offline jitter

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #132 on: January 14, 2016, 07:44:10 am »
How has this thread gone from a valve amplifier to an Apple thread?
 

Online Richard Crowley

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #133 on: January 14, 2016, 07:52:46 am »
How has this thread gone from a valve amplifier to an Apple thread?
Discussion of the future of headphone interface (connector, impedance, etc.) is threatened by Apple's rumored decision to drop the industry-standard analog headphone interface (3.5mm or 6.35mm=1/4 inch) presumably in favor of digital and likely wireless interface. Rendering the valve headphone amps, already arcane, to the category of downright obsolete as well.
 

Offline bob808

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #134 on: January 24, 2016, 11:41:33 pm »
 

Online Brumby

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #135 on: January 25, 2016, 01:53:36 am »
Much of the reaction is predictable - but one post made me smile.

This is probably the most honest attitude I have come across:
"My take is, even if there are no variables - all cables sound the same, all amps sound the same, all CD players and turntables sound the same (which of course I don't think is the case) the Fact that we Perceive improvements and gain increased enjoyment from them (even if in fact they aren't there) it's WORTH it. Perception is reality; not fact."

I have to agree that perception is the key factor in the appreciation of anything.  If someone feels happier about something that isn't real, then I can just shake my head and walk by quietly.

But have someone try to convince another that the extra $$$s are worth it - and I have a real problem.
 

Online Brumby

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #136 on: January 25, 2016, 01:56:41 am »
Then there was this:
"His parents should have put the lid back on the red cordial."

Yeah - sometimes you can wonder about that... but, in the end, it's an honest opinion that's as entertaining as hell.
 

Offline rrinker

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #137 on: January 25, 2016, 04:27:50 am »
 I laughed out loud at this one:

what irritates also are clowns like the guy in the video, he didn't really offer any factual information nor present as someone really capable of doing so.  At one point he mentions 'sheilding' as though it's a snake oil selling term and holds up his basic black IEC power cable as though it's performance can't be bettered.

LOL doesn't offer facts?  :-DD :-DD :-DD :-DD
 

Offline Pentium100

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #138 on: January 25, 2016, 07:03:49 am »
Even if, for example, the signal from a reel to reel tape deck is inferior to the signal from a CD player (most likely with my tape decks and tapes, definitely for some recordings I have), it is still more enjoyable to me to listen to music while watching the big reels spin.

Tubes usually do alter the signal (SE amplifiers, for example, usually have a lot of 2nd order harmonics), so it's a matter of preference. I, for example, prefer the sound of my (lo-fi) tube tape recorder for some music even though other music on it sounds bad.
 

Offline c4757p

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No longer active here - try the IRC channel if you just can't be without me :)
 

Offline kalleboo

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #140 on: January 25, 2016, 08:30:41 am »
The Wikipedia page posted above says that Apple sell a Lightning to 30pin (previous Ipod/IPhone connector) adapter and that it supports analog audio.
And it actually contains a small DAC!

Google brings up lots of knockoffs of this adapter, so maybe the work is already done?
The cheap ones I've seen in stores all say "Does not support Audio/Video" on the box, e.g. this one on Amazon: http://www.amazon.com/DP-30-Pin-Adapter-Apple-Lightning/dp/B00D48Q4OG
 

Online Fungus

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #141 on: January 25, 2016, 06:34:07 pm »
The Wikipedia page posted above says that Apple sell a Lightning to 30pin (previous Ipod/IPhone connector) adapter and that it supports analog audio.
And it actually contains a small DAC!

I don't trust it, it will have jitter.

Bring back the true analog output!
 

Offline krivx

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #142 on: January 25, 2016, 07:53:17 pm »
The Wikipedia page posted above says that Apple sell a Lightning to 30pin (previous Ipod/IPhone connector) adapter and that it supports analog audio.
And it actually contains a small DAC!

I don't trust it, it will have jitter.

Bring back the true analog output!

You don't trust the DAC in a cable, but a DAC inside the phone is OK?
 

Online blueskull

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #143 on: January 25, 2016, 09:23:17 pm »
You don't trust the DAC in a cable, but a DAC inside the phone is OK?

Clock directly driven by oscillator or SoC has much better jitter performance.
Clock recovered from USB is not, unless you go the async path and have a local oscillator, and discipline your data source to your local clock.
 

Offline rch

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #144 on: January 25, 2016, 09:48:28 pm »
You don't trust the DAC in a cable, but a DAC inside the phone is OK?

Clock directly driven by oscillator or SoC has much better jitter performance.
Clock recovered from USB is not, unless you go the async path and have a local oscillator, and discipline your data source to your local clock.

If it is mainly going to used to listen to music recovered from .mp3s I think that is a purely academic concern.  Even I can often hear gross compression artifacts, and I'm not musical.
 

Online Fungus

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #145 on: January 26, 2016, 01:36:19 am »
I don't trust it, it will have jitter.

Bring back the true analog output!
You don't trust the DAC in a cable, but a DAC inside the phone is OK?

I thought the "true analog" would have given it away, but nooooo....  :-DD

 

Online Brumby

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #146 on: January 26, 2016, 01:42:25 am »
The truth be known, Fungus wants his brick mobile phone back...
 

Offline gildasd

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #147 on: January 26, 2016, 02:23:45 am »
The truth be known, Fungus wants his brick mobile phone back...
Could a person even make* an all analogue GSM phone?


*That fits in the bed of a Medium Pickup and runs off no more than a Honda Handy generator of 700W.
I'm electronically illiterate
 

Offline mikerj

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #148 on: January 26, 2016, 04:16:24 am »
 

Offline bob808

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #149 on: January 26, 2016, 04:18:06 am »
I start to feel less and less sorry for them. I feel they should pay as much as possible for their arrogance :)
 

Offline Yansi

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #150 on: January 26, 2016, 05:13:49 am »
Drawing an  analogy to a J-FET is simply wrong.
A more apt analogy would be a MOS-FET since there is an insulator between the elements like in a vacuum tube.


Sorry Dave Ya got it wrong.

Sorry for the late reply, but comparison to a jfet is pretty much right. 

Both the tube's grid and jfet's gate behave the same way. Small capacitance for negative voltages, a diode for positive voltages (with respect to cathode / source).
 

Offline AF6LJ

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #151 on: January 27, 2016, 03:06:57 am »
Drawing an  analogy to a J-FET is simply wrong.
A more apt analogy would be a MOS-FET since there is an insulator between the elements like in a vacuum tube.


Sorry Dave Ya got it wrong.

Sorry for the late reply, but comparison to a jfet is pretty much right. 

Both the tube's grid and jfet's gate behave the same way. Small capacitance for negative voltages, a diode for positive voltages (with respect to cathode / source).
J-FETs have a lower impedance there is physical contact between elements, and a J-FET cannot operate with current flowing on the gate, a vacuum tube can.

I hate to put too sharp of a point on it but;
Drawing that analogy dumbs down the whole discussion. Vacuum tubes are unique as an active device, even though they share some commonalities with solid state field effect devices.
Sue AF6LJ
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Offline bktemp

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #152 on: January 27, 2016, 03:45:04 am »
Drawing an  analogy to a J-FET is simply wrong.
A more apt analogy would be a MOS-FET since there is an insulator between the elements like in a vacuum tube.


Sorry Dave Ya got it wrong.

Sorry for the late reply, but comparison to a jfet is pretty much right. 

Both the tube's grid and jfet's gate behave the same way. Small capacitance for negative voltages, a diode for positive voltages (with respect to cathode / source).
J-FETs have a lower impedance there is physical contact between elements, and a J-FET cannot operate with current flowing on the gate, a vacuum tube can.

I hate to put too sharp of a point on it but;
Drawing that analogy dumbs down the whole discussion. Vacuum tubes are unique as an active device, even though they share some commonalities with solid state field effect devices.
A J-FET can be operated with a current flowing into the gate. If the junction gets forward biased, current will flow. And this will decrease the drain-source resistance further.
The operating principle may be different, but electrically their behaviour is similar (Id/Ug curve), except J-FETs work on a much lower voltage than tubes and drain and source are interchangeable.
At the end of the tube era some tubes were substituted with a J-FET input stage driving a larger transistor.
 

Online Brumby

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #153 on: January 27, 2016, 03:23:26 pm »
Drawing that analogy dumbs down the whole discussion.

A simplification it may be - but that comment was still more intelligent than the product.
 

Offline Yansi

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #154 on: January 28, 2016, 01:28:40 am »
I don't feel offended when talking about the JFET analogy for tubes.  :)

It is an analogy, not a direct replacement having same operation voltage and same high impedances...
 

Offline AF6LJ

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #155 on: January 28, 2016, 02:02:10 am »
I am not offended; I feel the analogy dumbs down the subject.
Sue AF6LJ
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Offline Yansi

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #156 on: January 28, 2016, 03:59:26 am »
You seem to have a better analogy, don't you?   :D
 

Offline AF6LJ

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #157 on: January 28, 2016, 06:08:38 am »
You seem to have a better analogy, don't you?   :D

This one situation where an analogy serves no good.
Go learn how vacuum tubes actually work.

Just as a small example the J-FET analogy doesn't explain why a tetrode under certain conditions draws negative screen current.

Bad analogies are a trap for young players.
Sue AF6LJ
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Offline Pentium100

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #158 on: January 28, 2016, 08:23:57 am »
JFET is similar to a pentode (operating with the screen and suppressor grids connected to fixed voltages), but I do not think there is a solid state device that has the IV curves of a triode.
 

Offline Groucho2005

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #159 on: January 28, 2016, 08:34:01 am »
but I do not think there is a solid state device that has the IV curves of a triode.
Yes there is, Static Induction Transistor (SIT), some info here: http://www.firstwatt.com/sitintro.html
 

Online helius

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #160 on: January 28, 2016, 08:43:53 am »
Yes there is, Static Induction Transistor (SIT), some info here: http://www.firstwatt.com/sitintro.html
I was reading with interest until he said "First, it allows a single gain stage...without a feedback loop or degeneration." As is widely known, a triode amplifier doesn't work "without feedback": the feedback happens internally.
 

Online blueskull

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #161 on: January 28, 2016, 01:50:46 pm »
but I do not think there is a solid state device that has the IV curves of a triode.
Yes there is, Static Induction Transistor (SIT), some info here: http://www.firstwatt.com/sitintro.html

Their shit outputs 10W from 200W input at 4.5% THD at full load and 0.18% THD at no load??? :wtf:
 

Offline AF6LJ

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #162 on: January 28, 2016, 03:14:44 pm »
JFET is similar to a pentode (operating with the screen and suppressor grids connected to fixed voltages), but I do not think there is a solid state device that has the IV curves of a triode.

I haven't seen one...


In this day and age vacuum tubes are for the most part at the end of their technological evolution. The last place you will find vacuum tube tech used in are devices like ion implanters, Ion discharge machining and similar industrial applications, where the work is being done inside a vacuum with an electron emitter and grids, anodes and the like to accelerate ions.

Vacuum tubes are still fun to play with. :)
Sue AF6LJ
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Offline mikerj

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #163 on: January 28, 2016, 06:42:20 pm »
Their shit outputs 10W from 200W input at 4.5% THD at full load and 0.18% THD at no load??? :wtf:

Where did you get the 200W input from?  I see 18dB gain and 10W output.

The distortions figures are quite impressive for a single transistor power amp with no feedback, try getting anywhere near that with a single bipolar or MOSFET.
 

Offline Yansi

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #164 on: January 28, 2016, 10:35:15 pm »
AF6LJ: Yolo, there are also mosfet tetrodes. Usually HF stuff. Also behaving well like a tetrode (pentode) valve, having the g1 input capacitance ridiculously low.
 

Offline AF6LJ

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #165 on: January 29, 2016, 12:31:18 am »
AF6LJ: Yolo, there are also mosfet tetrodes. Usually HF stuff. Also behaving well like a tetrode (pentode) valve, having the g1 input capacitance ridiculously low.

I know about dual gate MOS-FETS They don't behave fquite like a tetrode but are a beast all their own.
Sue AF6LJ
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Offline Groucho2005

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #166 on: January 29, 2016, 02:47:27 am »
Their shit outputs 10W from 200W input at 4.5% THD at full load and 0.18% THD at no load??? :wtf:

Where did you get the 200W input from?
Go to the product page and look at the SIT1/SIT2 amplifier pages. Yes, this is an extremely inefficient design and there are barely any speakers it can drive properly.
 

Offline mikerj

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #167 on: January 29, 2016, 02:51:08 am »
Their shit outputs 10W from 200W input at 4.5% THD at full load and 0.18% THD at no load??? :wtf:

Where did you get the 200W input from?
Go to the product page and look at the SIT1/SIT2 amplifier pages. Yes, this is an extremely inefficient design and there are barely any speakers it can drive properly.

That's simply because they are Class A designs, which are inherently inefficient.  Pure class A amps with reasonable power outputs are room heaters, irrespective of the type of power output device.
 

Online Fungus

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #168 on: January 29, 2016, 02:53:47 am »
Go to the product page and look at the SIT1/SIT2 amplifier pages. Yes, this is an extremely inefficient design and there are barely any speakers it can drive properly.

It's a class A amplifier, so... that's just the way they work.

They're good for cold winter days. With a small enough heatsink you can even cook eggs.  :)

 

Offline Groucho2005

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #169 on: January 29, 2016, 04:02:03 am »
Their shit outputs 10W from 200W input at 4.5% THD at full load and 0.18% THD at no load??? :wtf:

Where did you get the 200W input from?
Go to the product page and look at the SIT1/SIT2 amplifier pages. Yes, this is an extremely inefficient design and there are barely any speakers it can drive properly.

That's simply because they are Class A designs, which are inherently inefficient.  Pure class A amps with reasonable power outputs are room heaters, irrespective of the type of power output device.
You have to differentiate a bit. Theoretically, a Class-A amplifier can have up to 50% efficiency. A Class A amplifier with complementary bipolar or MOSFET output devices comes very close to that number.
However, a single ended class a triode amp, which is very popular in the audiophile/audiophool community, will barely reach 10% efficiency which seems pretty insane but there are people who wouldn't have it any other way.

 

Offline rrinker

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #170 on: January 29, 2016, 07:17:33 am »
 The Class A design was used as a selling point for the receiver I had in college. Well, at full volume (this sucker goes to 11!), it would barely get warm. But at normal listening levels - yes, I could fry eggs right in my dorm room. All was fine until I developed a habit of going to sleep with the volume really low for background noise - fried the outputs twice on it.

 

Online Brumby

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #171 on: January 29, 2016, 01:01:13 pm »
That's the one thing about Class A amplifiers I always remembered ....  If you want them to run as cool as possible, you had to run them at full volume.
 

Offline retrolefty

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #172 on: January 29, 2016, 01:35:01 pm »
That's the one thing about Class A amplifiers I always remembered ....  If you want them to run as cool as possible, you had to run them at full volume.

 That sounds like a myth to me? Can you link to an analysis to support that.
 

Online Brumby

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #173 on: January 29, 2016, 03:32:04 pm »
Hmm...

My text books are buried somewhere if not long gone - and Google hasn't been too helpful.  I've found some references to power dissipation in Class A amplifiers, but nothing that gives me what I was looking for - which would be a chart of power dissipation vs output power.

It is my understanding that pure class A amplifiers draw maximum power from their supply at no signal (and therefore no output).  While not being particularly critical of my reading over the years, unless I've read it wrong, as power increased to the load, there is a corresponding drop in the power dissipated by the amplifier.  Therefore the amplifier runs cooler at maximum output.

I'm open to correction if I've got that wrong.

Will still keep looking for something to back it up - but I can't spend any longer on this right now.
 

Offline mikerj

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #174 on: January 29, 2016, 09:20:34 pm »

You have to differentiate a bit. Theoretically, a Class-A amplifier can have up to 50% efficiency. A Class A amplifier with complementary bipolar or MOSFET output devices comes very close to that number.

Not true for an equivalent design to the one shown in the SIT datasheet.  The efficiency of a simple class A design is no better than 35% at full load, and much worse at low outputs or under quiescent conditions.  Efficiency can be improved by using active loads rather than a simple resistor or transformer coupling, but even then you are unlikely to reach 50% efficiency.
 

Offline Groucho2005

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #175 on: January 29, 2016, 10:05:33 pm »

You have to differentiate a bit. Theoretically, a Class-A amplifier can have up to 50% efficiency. A Class A amplifier with complementary bipolar or MOSFET output devices comes very close to that number.

Not true for an equivalent design to the one shown in the SIT datasheet.  The efficiency of a simple class A design is no better than 35% at full load, and much worse at low outputs or under quiescent conditions.  Efficiency can be improved by using active loads rather than a simple resistor or transformer coupling, but even then you are unlikely to reach 50% efficiency.
I suppose you missed my use of the words "theoretically" and "up to". Also, efficiency obviously relates to the maximum power output.
Lastly, transformer coupling is much more efficient than using active loads.
 

Offline gadget73

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #176 on: February 03, 2016, 12:47:19 pm »
That's the one thing about Class A amplifiers I always remembered ....  If you want them to run as cool as possible, you had to run them at full volume.

 That sounds like a myth to me? Can you link to an analysis to support that.

Some amplifiers will switch in and out of Class A operation depending on output demands.  At low levels it runs a room-warming Class A bias level, with some crank it switches to a more sane AB1 bias level and the heat drops accordingly.  A straight Class A amp chugs out essentially the same heat with the volume at 0 or 11. 
 

Online Brumby

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #177 on: February 03, 2016, 01:10:32 pm »
That's the one thing about Class A amplifiers I always remembered ....  If you want them to run as cool as possible, you had to run them at full volume.

 That sounds like a myth to me? Can you link to an analysis to support that.

Best I've come up with so far...

http://www.analog.com/library/analogDialogue/archives/40-06/class_d.html

 

Offline coppice

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #178 on: February 03, 2016, 03:41:05 pm »
That's the one thing about Class A amplifiers I always remembered ....  If you want them to run as cool as possible, you had to run them at full volume.

 That sounds like a myth to me? Can you link to an analysis to support that.
It comes directly from the definition of class A. A pure class A amp draws a constant amount of power. At zero output it all ends up as heat in the amp. At maximum output some ends up in the load, so less ends up as heat in the amp.
 

Online Brumby

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #179 on: February 03, 2016, 03:49:47 pm »
That's what I was talking about!  Thank you.  :-+
 

Offline FM

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Re: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier
« Reply #180 on: July 06, 2016, 08:30:54 am »
If my really quick look is correct, it looks like you can remove the valves and jumper pin 2 (control grid) to pin 3 (cathode) and get a much lower power, halfway decent headphone amp.
Can anyone confirm that method to bypass the tubes? 
It would lower the power by a lot?
I wish another video was done on this amp about bypassing the tubes.

This amp gets criticism for the tubes not doing much, but if bypassing the tubes doesn't lower the power output, it's a lot of power for the price, and bypassing the tubes means no need to buy replacement tubes when the stock ones wear out.  And it gets rid of the tube distortion, of course.

I have one and like it, but it'd be great to be able to bypass the tubes.  If the power output would be the same. 
 


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