John Curl's Blowtorch preamplifier part II

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BV, these subtraction tests are interesting, but they don't seem to be enough. IF they are 'enough' then buy a used Hafler amp and enjoy the audio experience forevermore.
Walt Jung's, Scott Wurcer's and my experience with just a single CAP difference test was difficult to null, even with one of the best IN-AMP's at the time (120dB rejection) and ultra fine adjustment.
I can just imagine the compromises in whole amp difference tests.
What we seem to be looking for is subtle, perhaps near or at the level of perception of sound, yet different enough from other signals to be noted in some way by the ear-brain system by many people of all ages. It is most likely a survival mechanism separating normal environmental sounds from something unusual.
Can I personally prove this? No, not at this time, but it appears to be what is happening.
Should I tell anyone this? Without absolute proof or backup? Well, many here could just happily live in ignorance of what some serious researchers are looking at today. Perhaps, even the mention of such an idea is considered inappropriate, by some. I really don't know, but personally, I would welcome such input, and help contribute to whether it is as important as it seems to be.
 
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Why I have to PROVE everything to a bunch of skeptics, who are so insulting as to call me 'intellectually dishonest' or not forthright in my explanations of how to design an amp, is beyond me.

Hi John

I just passing by and haven’t read all posts the last days.

I don’t think you have to prove everything to a lot of sceptics.
There are some people that are more sceptical than others, and if somebody called you what you are saying I hope they regret it.

Hopefully it’s possible to disagree or being sceptical without using such phrases.

Just a question, when you did the tests back in the 70’s, did you do the tests only once or did you repeat the test a number of times and did you do the test with 741’s from another batch?

If you did the test a number of times, did it show the same spectrum?

Cheers
stinius
 
Come on John... It is a well known fact, about audibility of in-natural sounds. But every time myself, or somebody else expresses this fact, or tries to prove it, or to illustrate on examples, you do everything you can to shut us up, as if you want to be The Single Man Who Saw The Moon, while The Whole World is Against You. It looks like you are knocking hard in already wide open gates. :)
 
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Hi John,
Demian has completed a test board that we might use together to do some additional measurements, such as the original TIM test.
I have requested the information so that I may also try the TIM test - repeatedly. The way I see things is simple. See if the test can be repeated, then explain the results.

I also have the required equipment to run this test. Is it a case that only people you trust will be trusted with the test details? I mean, it keeps you pretty safe, doesn't it?

Anyway, I have many times stated that I both listen and test. I do hear things I can't test for, never said I didn't. But I always attempt to find a way to quantify what I'm hearing, simply to be able to have a standard that does not change over time as the human subjective experience will. Yet you still take pains to exclude myself and many others here who also listen to their work and hear differences, as well as test with equipment.

So, do you want to show the way? Allow us to test and hear for ourselves what you have heard? These are the real questions here. Once we can reproduce what you have seen, we can discuss the observations more intelligently. Your exclusive nature is not helping your cause, turning possible supporters into people with reasonable doubt.

-Chris
 
Sorry Stinius, while I made the same tests as that presented in the paper, my results were lost in a firestorm in 1991. I doubt that there is anything wrong with the test results, or the 741 IC used.
Maybe, just maybe, any discussion of audio differences is a waste of time. It could well be that the ear imagines things, and that virtually all audio electronics sounds similar, and exceptions have something wrong with them. Of course, I don't know why people come here to deny anything that I talk about, when they could be doing more productive things. I often wonder what I am doing here, myself.
It does appear that if I just disappear from this thread, it goes away. Yet when I try to steer clear of obvious debates in the past, the very same questions and insults come back, by the same people, almost immediately. Why is this? Can't you each have your own thread? Can't each design philosophy be put forth independently, without 'crosstalk' from a skeptic?
 
Demian has completed a test board that we might use together to do some additional measurements, such as the original TIM test. Demian and I, both, have the test equipment to do the job.

Just curious, what is your expectation regarding these measurements?

Are you ready to disclose the whole setup so that others could reproduce your results?


And have you seen Gerhard's measurements posted a couple of weeks ago? Any comments about?
 
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Chris,

If I understood Bob's earlier posts correctly, he showed that with a forward path with no PIM, and a linear feedback path, you can generate PIM.
Is that correct? Bob?

jd

Hi Jan,

That is exactly right. The application of negative feedback to a PIM-less amplifier may cause amplitude-to-phase conversion; in other words, some of the AIM gets converted to PIM. The AM-to-PM conversion results because the incremental changes in open-loop gain (AIM) cause the NFB unity gain crossover frequency to move around, causing the closed loop bandwidth to move around, causing the in-band phase to move around, and thus a small amount of phase modulation.

Because the AM-to-PM conversion is of only modest efficiency, it is virtually impossible to have PIM from this mechanism without having AIM. If you drive the AIM down to extremely low levels, you will necessarily drive any PIM down to extremely low levels.

Cheers,
Bob
 
Hi Jan,

That is exactly right. The application of negative feedback to a PIM-less amplifier may cause amplitude-to-phase conversion; in other words, some of the AIM gets converted to PIM. The AM-to-PM conversion results because the incremental changes in open-loop gain (AIM) cause the NFB unity gain crossover frequency to move around, causing the closed loop bandwidth to move around, causing the in-band phase to move around, and thus a small amount of phase modulation.

Because the AM-to-PM conversion is of only modest efficiency, it is virtually impossible to have PIM from this mechanism without having AIM. If you drive the AIM down to extremely low levels, you will necessarily drive any PIM down to extremely low levels.

Sure, and I see 3 obvious ways to drive AIM down: to linearize each and every stage's complex transfer function, to linearize (or at least decrease) their output complex impedances and linearize (or at least increase) their input complex impedances, and increase bandwidth of each and every stage. Such a way a global feedback will be much more in-phase with errors over the whole audio band, so very small amount of PIM would be created as the result.

John,
The issue you addressed is the never-ending debate between some engineers and audiophiles.

Come on Joshua... Why such wide generalizations are needed here where engineers are honestly searching for ways to improve sound quality?
Who we are in your generalization, heretics who are both audiophiles and engineers, or heretics who are neither audiophiles nor engineers?
I can show my diploma to prove that you are wrong in one part of your statement, and I can show you my equipment to show that you are wrong in another part of it. There is no debates between engineers and audiophiles here. Those who agree about PIM creation mechanisms don't see proof of their presence on the graph, because from that graph it is impossible to distinguish AIM from PIM.
 
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Come on Joshua... Why such wide generalizations are needed here where engineers are honestly searching for ways to improve sound quality?
Who we are in your generalization, heretics who are both audiophiles and engineers, or heretics who are neither audiophiles nor engineers?
I can show my diploma to prove that you are wrong in one part of your statement, and I can show you my equipment to show that you are wrong in another part of it. There is no debates between engineers and audiophiles here. Those who agree about PIM creation mechanisms don't see proof of their presence on the graph, because from that graph it is impossible to distinguish AIM from PIM.


I wrote some engineers – not all engineers. So, here goes what you refer to as "wide generalizations".

Now, I'm not so sure that all engineers participating in this thread are "honestly searching for ways to improve sound quality". Some definitely do. It seems to me that some others are stuck with their text books. That is, some are negating genuine subjective experiences, unless proven by methods subscribed in their text books. Meaning, they ignore heard PIM (or TIM, or whatever other type of distortion), unless they see it on the graph.

Generally speaking, hard-core audiophiles (with an engineering degree or without it) rely mainly on their ears (actually, the brain-ears mechanism), while engineers who are not audiophiles rely mainly on measuring equipment. Of course, there are engineers who are audiophiles, or audiophiles with a scientific, or technical background – however, they are a third group of people – who rely on both ears and measuring equipment.

It seems to me that it takes a degree of intellectual honesty to admit that science today don't have all the answers for what impacts the experience of listening to reproduced music.

Yet, obviously, I may have the wrong impression. Possibly, all here agree on the basics, only debating on the means.
 
Sure, and I see 3 obvious ways to drive AIM down: to linearize each and every stage's complex transfer function, to linearize (or at least decrease) their output complex impedances and linearize (or at least increase) their input complex impedances, and increase bandwidth of each and every stage.

What you say may be valid in the context of a voltage amplifier target. Which is not necessary always the case.
 
What you say may be valid in the context of a voltage amplifier target. Which is not necessary always the case.

Exactly.

In a power amplifier case linearity of each stage, linearity of coupling between them, and high bandwidth of each stage is the way to go. However, I mean complex linearity. Add here minimal power loss between stages and you have the whole equation of a desired amp with minimum of AIM that create minimum of PIM after GNFB applied. By the way, it is the way Otala's pupil designed his amp in order to replace Williamson tube amp version his wife did not like.

It seems to me that it takes a degree of intellectual honesty to admit that science today don't have all the answers for what impacts the experience of listening to reproduced music.

Not at all. Everyone who knows how science does work should know the difference between (the best scientific) models and The Reality.
 
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Exactly.
Add here minimal power loss between stages and you have the whole equation of a desired amp

Careful here. The minimum power loss (or maximum power transmission) condition is on a collision course with either voltage or current optimal coupling. In audio we care about voltage or current gains (or linearity) rather than power gain (or linearity).
 
Good to see you here, Joshua.
What is amazing is: If it looks like a duck, quacks like a duck, maybe it is a duck, except everyone here is insisting that it is a swan, or that it is an optical illusion.
When it comes to FM modulation, I will, once again say: The pattern looks like FM, the cause seems to come from Barrie Gilbert's analysis, yet nobody wants to presume that it might be FM distortion. What is the problem? Politics and denial. If true, it 'implies' that traditional op amps can be troublesome. Wow, what a concept! As if we don't know something subjectively about that, today. The problem is that the traditional measurements don't show anything.
 
Demian,
the harmonic and inharmonic content of musical instrument sounds is for the instrument makers to deal with. Our aim is a faithful reproduction of those sounds so you can discern the difference between a Steinway and a Bösendorfer. As a first step, stay far away from Op-amps.
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John,
regarding who is telling anecdotes and muddying waters, I tend to support you.
 
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