Author Topic: EEVblog #837 - Reverse Engineering A Valve Headphone Amplifier  (Read 48122 times)

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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.
 

Offline 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?
 

Offline 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?
 

Offline 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 »
 


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