Hawksford

Status
Not open for further replies.
Jump to Latest
#221
fab said:
Maybe it is not necessarily bad to have the collector resistors to ground at the VAS output? Is it possible that a properly selected value for these resistors could "stabilize" the open loop VAS gain so it is not affected by the load under high power conditions?
Click to expand...

Hi Fab,

Interesting idea. Nelson indicated that the measured distortion increased when he tried it, but the subjective sound quality improved. But could there be a case where the measured distortion would improve? Maybe. If there wasn't adequate current gain in the output stage, then there could be a problem with badly nonlinear loading of the VAS. A shunt resistor would improve this. The question then becomes whether the increased VAS current swing and decreased feedback would be more than compensated by the better linearity of the load of the VAS. I suppose it's possible. But with adequate output stage current gain, you'd be better off from the standpoint of measured distortion to leave the resistors out.
 
#222
Inadequate output stage current gain is a real problem. It's definitely one of the blind spots of Self, and also one of the virtues of the Leach design. (Leach's output stage was taken directly from Bart Locanthi's "T-Circuit" of 1966.)

And that doesn't change the fact that the correlation between measured performance and audible performance is exceedingly weak at best.

True story -- There's a guy named Andrew Hefley that is a very good solid state designer. Do a web search and you'll see he has a long and distinguished resume. You can even see some of his circuits in an app note he wrote for Motorola (now available at On Semiconductor).

About six or eight years ago, he heard his first single-ended triode. And do you know what he did? He quit the business. Now he makes instrumentation for light aircraft.

He told me that after 30 years of designing solid state audio amps that he figured he knew it pretty well. But after hearing the SET, it showed him that pretty much everything he knew and believed was wrong. Instead of going back to the drawing board, he literally quit the field.

There are other guys here, like Nelson, who didn't quit. Instead, they started exploring a completely different approach than "perfect steady-state performance on a test bench into a resistive load".

Thinking is good. Listening is better. Listening and thinking about what you are hearing is best.
 
#223
Re: How do you know what Nelson can or can not do?

Jocko Homo said:
I know one thing that he can do:

Make amplifiers that have met the acceptance of many consumers, over a considerable period of time.

Not an easy feat.

And his critics have done..............?.......what........?...is that silence that I detect?


Oh, yeah.....I know.....write articles on how he doesn't know squat about SOA.


Jocko
Click to expand...

http://www.sjostromaudio.com/jocko_homo.html
 
#224
Re: Re: Theory versus Practice

charles hansen[/i] [B] As usual said:


It's expected that theory won't in general be born out by non-scientific practice. And I don't think Nelson's making the claim that his final decision was based on a scientific approach. He just went with what sounded better to him. Nothing wrong with that. If you consider the scientific portion of what he said though, namely:

then the theory was born out in practice. Loading down the VAS increased the distortion consistent with the theory.
Click to expand...


Hi Andy,

Have to say i admire your restraint in the face of Charles' condescension.....i will try to follow your example... :nod:
 
#226
Charles Hansen said:


There are other guys here, like Nelson, who didn't quit. Instead, they started exploring a completely different approach than "perfect steady-state performance on a test bench into a resistive load".

Thinking is good. Listening is better. Listening and thinking about what you are hearing is best.
Click to expand...


Just do both. Measure and listen and try try to improve one by improving the other. Compare your result with results of the others (both sonically and on the workbench). This is the way, not to be deaf and blind.
 
#227
Re: The folly of youth...

Charles Hansen said:


Actually, I'd be willing to bet that you're the one doing the "patronising". Why? Because I doubt you've taken the time to do the listening tests yourself.
Click to expand...

Actually...i have listened to music through many amplifiers including Nelson's.....

......and i have recently participated in a double-blind test.......

.....which merely proved that any 'differences' i perceived during casual uncontrolled sessions of the sort you are aluding to, were entirely illusory.....

These are simple statements of scientific fact, and not unproven speculation....i don't think it's necessary to bother going over this terrain.......
 
#230
Re: Re: The folly of youth...

mikeks said:


Actually...i have listened to music through many amplifiers including Nelson's.....

......and i have recently participated in a double-blind test.......

.....which merely proved that any 'differences' i perceived during casual uncontrolled sessions of the sort you are aluding to, were entirely illusory.....

These are simple statements of scientific fact, and not unproven speculation....i don't think it's necessary to bother going over this terrain.......
Click to expand...

Could you in detail describe the whole audio chain you have used for testing, listenning room, positionning of speakers in the room and the method of switching (box or exchanging cables, length of musical fractions used, kind of music).

These tests can be arranged to meet the demands, regardless they are "objectivictic" or "subjectivistic".
 
#233
andy_c said:


Hi Fab,

Interesting idea. Nelson indicated that the measured distortion increased when he tried it, but the subjective sound quality improved. But could there be a case where the measured distortion would improve? Maybe. If there wasn't adequate current gain in the output stage, then there could be a problem with badly nonlinear loading of the VAS. A shunt resistor would improve this. The question then becomes whether the increased VAS current swing and decreased feedback would be more than compensated by the better linearity of the load of the VAS. I suppose it's possible. But with adequate output stage current gain, you'd be better off from the standpoint of measured distortion to leave the resistors out.
Click to expand...

Hi andy_c

Thanks for your comments.
Regarding the decrease of THD with higher open loop gain I can not argue with that but like anything in life: maybe we have to make compromises to design an amp taking into consideration our own objectives. For example, if the shunt resistor increases slightly the THD and the THD is already low, then it is theoritically possible that this resistor of known value could provide a more stable VAS gain at all audio frequencies and audio power levels when driving more complex load impedance (speaker) than purely resistive 8 ohms. This may also be pure speculation from me since I did not perform a deep analysis nor controlled measured experiments to prove that. What I observed though is that this VAS shunt resistor is used in a lot of amp designs I have seen. So I suspect that it must not be so useless, no?

Fab
 
#234
Re: Re: Re: The folly of youth...

PMA said:


Could you in detail describe the whole audio chain you have used for testing, listenning room, positionning of speakers in the room and the method of switching (box or exchanging cables, length of musical fractions used, kind of music).

These tests can be arranged to meet the demands, regardless they are "objectivictic" or "subjectivistic".
Click to expand...

This ground has been covered to death....here:

http://diyaudio.com/forums/showthread.php?s=&threadid=12752
 
#235
Re: Re: Re: Re: The folly of youth...

mikeks said:


This ground has been covered to death....here:

http://diyaudio.com/forums/showthread.php?s=&threadid=12752
Click to expand...

Thanks for the link.
The reason why I ask is that I have quite different experience from the listenning tests (difference is clear, evident). And I also went through the stage when "everything sounded the same" 😉
 
#236
fab said:


This may also be pure speculation from me since I did not perform a deep analysis nor controlled measured experiments to prove that.
Click to expand...

Nothing wrong with speculation.......infact it is to be positively incouraged as a precursor to a proper scientific investigation......

But unlike Charles Hansen, do not fall into the trap of confusing such speculation with proven facts........

fab said:


What I observed though is that this VAS shunt resistor is used in a lot of amp designs I have seen.
Click to expand...

True......

fab said:


So I suspect that it must not be so useless, no?

Fab
Click to expand...


...Completely useless and ill concieved.....In all respects.....🙁
 
#237
Re: Re: Re: Re: Re: The folly of youth...

PMA said:


..... I also went through the stage when "everything sounded the same" 😉
Click to expand...


Hi Pavel...

please don't get me wrong here.....i actually went through the stage where everything sounded different.....

Indeed, everything still does, but i am now enlightened enough to know when my brain/ears are playing tricks on me....
 
#238
Mikeks, I'm curious about one thing. Since all amps sound the same to you, why do you waste your time hanging out here on these forums? After all, you could curl up happily on your couch listening to your Radio Shack amplifier (as good as anything ever made) instead of arguing with people like me and Pavel.
 
#239
Charles Hansen said:
Since all amps sound the same to you...
Click to expand...


No.........all amps. do not sound the same to me in a system context......eg some are obviously under powered.....others have hopelessly and audibly misconceived SOA protection.......etc.....

But these are flaws that are easy to diagnose.....no magic involved.....

Charles Hansen said:
....instead of arguing with people like me and Pavel.
Click to expand...

I reckon 'debating' is the word you're looking for...
 
Status
Not open for further replies.
Top Bottom