Author Topic: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier  (Read 46709 times)

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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.
 

Offline 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?
 

Offline 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.
 

Offline 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!
 

Offline 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
 


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