John Curl's Blowtorch preamplifier part II

[Wavebourn]

Originally Posted by syn08

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).

In audio I personally care of power gain; however with non-linearities in mind, from other side. Especially dealing with SS devices you can't get both at once.
I never tried to load infinitely high output on infinitely low input; however I used similar things deliberately creating guitar effects, but never tried for a high-end audio. How good are OL parameters of such a thingy? You should know better than me...

Originally Posted by john curl

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.

I will, once again say: it might be the result of PIM, but might be not. I did not follow this thread carefully when assumed that you have a proof because of asymmetrical sidebands, but you denied that, saying that sidebands are equal. That means, no proof at all.
Non-harmonic content can't prove presence of PIM. It may prove presence some say thermally-induced oscillations that cause something not related to signal spectra, or harmonic content may look like non-harmonic when intermodulaions occur between periodic signals and their envelopes (discussed with Jan Didden), but no way non-harmonic content can signify presence of phase modulation.

"Amicus est Socrates, magister meus, sed magis est arnica veritas." (C)

[Joshua_G]

Originally Posted by Wavebourn

Exactly.
Not at all. Everyone who knows how science does work should know the difference between (the best scientific) models and The Reality.

Originally Posted by john curl

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.

Originally Posted by Lumba Ogir

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.

Agreed wholeheartedly.

[anatech]

Hi John,
I really do think you need to read other people's responses more carefully.

Many people have now pointed out the normal and proper way to investigate any phenomenon. You discover something that you make note of. You recreate the observation, and once you can do that reliably, you make sure you don't have an error in the experiment. Once you are sure no errors have been made, you invite peer review and perhaps write a paper on your work. This would include the exact test setup, stimuli (test signals) and any other pertinent information so that your observations can be replicated by others. In this case, you want to see other experimenters come up with the same data. At this point, conclusions are not important. It's the validity of your experiment that is the critical question.

Anatech, just look at fig 1, of our paper on TIM. The test setup is there.

Thank you. I had asked if that diagram accurately represented your test setup a long time ago and got no response from you.

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.

That is a twisted analogy you used. It should read more like this ....
"If it looks like a duck, quacks like a duck, maybe it is a duck, or just possibly it's a decoy, a smudge on your glasses or whatever else was in the bottle along with the alcohol".

Note that I'm not suggesting that you drink, just looking at a better comparison. Now, you say it was a duck. Did you manage to get a picture so we can all have a look?

As said before by many other members, we can accept things exist that can not be measured at this time. No argument there, so you can drop that issue.

More than one member has expressed interest in running your experiments as close to the original set as possible. The hope is that others can recreate what you were seeing. This is not an attack of any kind. This is called "peer review", and this is part of any technical announcement. You can not expect for a moment that anyone will simply drop what they know in order to accept what you are telling them without any experimental data or other proof. You wouldn't, but you are expecting everyone else to do exactly that. Can you see why you are being questioned about these things John?

Now, for the benefit of all members, would you please draw out your experiment exactly, along with signal levels and any other information that might be required? This would go a long way to unifying everyone here and get them onto your page. Then you can talk about these things in a meaningful way.

-Chris

[PMA]

Regarding audible vs. inaudible - some people are easily able to tune the guitar, some are not and do not hear it is out of tune - they would need a frequency meter to tune it and tell if it is tuned. Why to expect that hearing abilities are same for all people?

[Wavebourn]

Originally Posted by PMA

Regarding audible vs. inaudible - some people are easily able to tune the guitar, some are not and do not hear it is out of tune - they would need a frequency meter to tune it and tell if it is tuned. Why to expect that hearing abilities are same for all people?

Also, hearing and perceiving are different things.

[BV]

Originally Posted by PMA

Regarding audible vs. inaudible - some people are easily able to tune the guitar, some are not and do not hear it is out of tune - they would need a frequency meter to tune it and tell if it is tuned. Why to expect that hearing abilities are same for all people?

But what if we "hear" something (zero signal in substraction test) what is not present??
Mr. Curl, I posted in this thread some pictures. One show the same spectra, as 741, and it is simple two diodes limiter. It is FM ?

[1audio]

The point I was making about the reference to the piano tuning was that a harmonically correct distortion that should sound like normal instrument harmonics may actually not correspond to the real sound and to a sensitive listener may sound "wrong". The point of this observation is that we can't accept any generalization on the audibility of distortions or lack thereof. The assumptions need to be tested.

As for linear distortions I belive it is accepted that very small frequency response errors, on the order of .1 dB over a large range, can be heard. However small peaks and dips can be very hard to discern. I know from experience small changes in RIAA eq can have a major effect on the perceived sound, but sonically don't match what the actual change was.

[jan.didden]

Originally Posted by anatech

Hi,
Does anyone have access to "Intermodulation Distortion in Tape Recording" Robert Z. Langevin JAES July 1963 Vol. 11, No. 2.

It's been referred to as basic material for this discussion by John.

-Chris

Chris:

http://www.linearaudio.nl/Miscellane...0recorders.pdf

I had a cursory look and it appears that the paper addresses all those 'unexplained' spectral lines in the famous Fig 3.

jd

[jan.didden]

Originally Posted by Bob Cordell

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

Right, thanks. Although the effect can be minimized by the same measures that minimize AIM and THD, some applications can be more sensitive to it, for instance because of sensitivity to slew rate limiting. An example would be an I/V converter where very high input slew rates are encountered. In this case you can have relatively large OL gain and phase modulation which, as Hawksford maintains, could even be considered as the analog equivalent of jitter - and sound similarly.

jd

[jan.didden]

Originally Posted by Joshua_G

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.

Joshua,

You are missing the point of these discussions massively. It is not about whether science has answers or not. It is not about whether PIM or TIM exists or can be audible. That is not contested as such.
The discussion is about answering questions about a statement that is made, about providing arguments that support your position so that others can judge for themselves instead being limited to 'believe' or 'not to believe'. Providing full details of your measurements, so that others can repeat them and either confirm or falsify them.
In other words, intellectual honesty.

jd