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John Curl's Blowtorch preamplifier part II
John Curl's Blowtorch preamplifier part II
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Old 7th December 2017, 10:38 AM   #98071
gpapag is offline gpapag  Greece
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John Curl's Blowtorch preamplifier part II
Quote:
Originally Posted by PMA View Post
frequency dependence of the output impedance
Relevant
http://www.ti.com/lit/an/slyt677/slyt677.pdf

George
Attached Images
File Type: png Op Amp Ro and Rout.PNG (186.6 KB, 206 views)
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Old 7th December 2017, 11:09 AM   #98072
PMA is offline PMA  Europe
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Quote:
Originally Posted by gpapag View Post
No. What I mean is a crossover nonlinearity of output impedance of class B/AB amplifier. It is not discussed here in cycles, it is not a "popular" theme. As attached and then measured at several frequencies. A "hint" for "pros" here.
It is neither a textbook, nor datasheet method and info.
Attached Files
File Type: pdf outimp6.pdf (64.3 KB, 69 views)
File Type: pdf outimp5.pdf (80.5 KB, 55 views)

Last edited by PMA; 7th December 2017 at 11:20 AM.
 
Old 7th December 2017, 11:48 AM   #98073
Tournesol is offline Tournesol  Belgium
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Quote:
Originally Posted by dadod View Post
Richard, nobody commented this extraordinary test result.
The silence that follows Mozard is still from Mozart.
And this with an evil current feedback ?
Hats off, dadod.
Quote:
Originally Posted by PMA View Post
No. What I mean is a crossover nonlinearity of output impedance of class B/AB amplifier.
What kind of "nonlinearity" do you expect from an amp able to produce 0.00024% of distortion at 100W 1kHz (100W 10KHz 4Ohms = .0057%) under load ?
BTW, what are the dumping factor and slew-rate (with no input filter nor output L) ?

Last edited by Tournesol; 7th December 2017 at 12:08 PM.
 
Old 7th December 2017, 12:04 PM   #98074
jan.didden is offline jan.didden  Europe
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Quote:
Originally Posted by PMA View Post
No. What I mean is a crossover nonlinearity of output impedance of class B/AB amplifier. It is not discussed here in cycles, it is not a "popular" theme. As attached and then measured at several frequencies. A "hint" for "pros" here.
It is neither a textbook, nor datasheet method and info.
This is very illustrative Pavel, great test!

Jan
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Old 7th December 2017, 12:20 PM   #98075
PMA is offline PMA  Europe
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Thank you Jan, and you do not need expensive instrumentation to make the test.

I can say that a well engineered class AB amplifier with optimum bias does not behave the way I have shown. No spikes on sine of the forced output and X-Y at 10kHz is a regular ellipse.
 
Old 7th December 2017, 12:36 PM   #98076
Jakob2 is offline Jakob2  Germany
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Originally Posted by Zaphod Beeblebrox View Post
You do make some excellent points. That said, the obvious conclusion is that the differences are either non-existent (highly probable, given the nonsensical 'physics' that the devices is allegedly designed around) or minute.
Thatīs the problem with such tests, bias and prior belief. We all know that no perfect experiment exists but if we choose to accept or neglect possible variable because the results of an experiment suit our prior beliefs there is high risk of observing a selffullfilling prophecy.

Quote:
Originally Posted by Zaphod Beeblebrox View Post
My recollection is that somewhere between a dozen and 15 or so. Each had the opportunity to test the devices in their own system, at their leisure. There was no pressure from peers.


Of course. Listeners knew that one pair of boxes contained ByBee devices and one pair of boxes contained equivalent value resistors.

Yes. Listeners knew that they were testing ByBee devices. IF I had to guess, I would say that half the listeners were sceptics and the other half open minded (I prefer the term 'uncritical').
As said before, the "unnormally" high proportion of "no difference/preference" votes raised my concern, as it is known from several studies/experiments (see for example the afore mentioned crosscultural study) that in preference tests proportion of "wrong answers" in the case of evaluating identical stimuli is usually in the range from 65-80% .

AS youīve said already, the impact of words or prior belief might be strong and without additional controls it is impossible to conclude about the results of "sceptical" participants. It is a good countermeasure to hide the effect under tests in these cases. Would not prevent participants from exspecting something (seems that humans always do exspect something) but would minimize the impact of prior belief.

Quote:
I have to acknowledge that the test lacked excellent rigor, but it was instructive in any case. Blind testing of ByBees seems to reveal little or no difference from resistors.
In your case it revealed "little to nothing" but we canīt really conclude about the reason due to the methodological points we have mentioned. "minute" or "no effect" might be true, but ....
 
Old 7th December 2017, 12:54 PM   #98077
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The point is that the manufacturers of these devices advertise a black and white difference. No amount of bias would account for not hearing changes on the level of the claims they make.

I don't see why we should give them any benefit of the doubt. The burden of the proof is on them. Discussing ad infinitum about how subtle the changes might maybe, on a good day, with the proper system, with the good listeners be audible is just a way of giving them a credibility they don't deserve.
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Old 7th December 2017, 01:18 PM   #98078
Jakob2 is offline Jakob2  Germany
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Originally Posted by 00940 View Post
The point is that the manufacturers of these devices advertise a black and white difference. No amount of bias would account for not hearing changes on the level of the claims they make.
Having not seen that "night and day difference claim" myself i nevertheless understand your point.
But, imo there is no widely accepted definition for "night and day" or "big difference" nor is it a given that a difference below that level canīt be or relevance (at least to some listeners).

Testing for "night and day" difference (assuming my definition) is totally different from testing trying to catch every difference. But, if you have tested for "night and day" you canīt claim having found that "no difference" or "only minute difference" possibly exist.

Quote:
I don't see why we should give them any benefit of the doubt. The burden of the proof is on them. Discussing ad infinitum about how subtle the changes might maybe, on a good day, with the proper system, with the good listeners be audible is just a way of giving them a credibility they don't deserve.
Itīs absolutely valid point of view to express that one does not follow their "technical" explanations, does not belief in any possible audible difference and would only accept hard facts from scientific experiments.

But otoh we know (see our recent mention/discussion of inattentional blindness/deafness) that even quite large differences can slip through due to confounders.

Furthermore i hope that people do realize that there is a lot to consider which hopefully helps them when doing some tests for evaluation purposes.
Just because every consumer has to decide if something is of relevance; even if a manufacturer provides hard facts, does it mean that it is of importance to every listener? Does anybody has to buy "blind" (scr) due to the fact that somebody was somewhere, somehow able to detect a difference?
 
Old 7th December 2017, 01:32 PM   #98079
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Quote:
Originally Posted by PMA View Post
Thank you Jan, and you do not need expensive instrumentation to make the test.

I can say that a well engineered class AB amplifier with optimum bias does not behave the way I have shown. No spikes on sine of the forced output and X-Y at 10kHz is a regular ellipse.
Indeed. The information you showed is basically the same data as comes out of the famous 'wingspan' curves as often used by Doug Self. In fact, one probably can turn the same data into either form of graph.

But your presentation is more expressive.

Jan
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Old 7th December 2017, 01:35 PM   #98080
gpapag is offline gpapag  Greece
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John Curl's Blowtorch preamplifier part II
Quote:
Originally Posted by PMA View Post
No. What I mean is a crossover nonlinearity of output impedance of class B/AB amplifier
Thanks Pavel.
This is the remaining part of your #98030 post (from which I selectively quoted ) about which I would like to ask you a simple schematic of the test setup, so I can understand what the plots really show and hopefully to replicate it, I am not a pro.
The last attachment of post #98052 show an amplifier with Rout=0.035 Ohm, yes?

George
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