Complex Load for Power Amplifier torture testing

[LTig]

When you say that in electronics, no-one has yet demonstrated that anything beyond relatively simple measurements in necessary, I find that a difficult statement to swallow. It would be quite easy to build a machine that gets great static THD and IMD yet is terrible for reproducing real music.

I'd love to see a blueprint for such a machine. Would it resemble existing machines?

Human perception of sound is also a difficult one to work with, as we have multiple sensor networks in our ears that don't just measure sounds in one way. At the very least we know there is something like an FFT machine that perceives different frequencies directly, plus there are other "edge" detectors which help us with soundfield positioning/localization. .

AFAIK the sound field localization is done by the brain.

 

[SIY]

I won't dispute your comment that experiences need to be validated in some sense to be related to the topic at hand, but ... to be more concrete:

Science is a process of creating models and testing of models through experiments, taking data, and data interpretation. The "model" you use is hopefully related to the reality around us, and that very much *also* requires validation. The models of gravity have been revised multiple times throughout history, to the point where we now have what the scientific community considers an extremely accurate model (Einstein's General Relativity) where singularities in the equations lead to situations that we don't understand. My point being that it is a human endeavor where finding models that match a wider array of data is valuable.

When you say that in electronics, no-one has yet demonstrated that anything beyond relatively simple measurements in necessary, I find that a difficult statement to swallow. It would be quite easy to build a machine that gets great static THD and IMD yet is terrible for reproducing real music. Static THD and IMD are just proxies for the quality of an audio channel which have been found to be pretty reasonable on audio chains otherwise designed to handle the full bandwidth of human-perceivable frequencies.

Human perception of sound is also a difficult one to work with, as we have multiple sensor networks in our ears that don't just measure sounds in one way. At the very least we know there is something like an FFT machine that perceives different frequencies directly, plus there are other "edge" detectors which help us with soundfield positioning/localization. We also know that many humans seem to *like* some kinds of distortion, commonly referred to as a "Tube-y sound" since analog audio chains built with vacuum tubes can often be tuned that way.

So my curiousity about non-THD/IMD measurements and how variations in them might affect human perception came about because I'd had some experiences in audio equipment of essentially equivalent THD/IMD producing perceptibly different soundfield results. I'm not claiming that this obviates the science of "better audio quality", simply that I'm curious about how that might come about, or was I just strongly confused by something. I've been slowly setting up to perform some experiments on audio drivers, non-linearity in sound reproduction, and seeing if I can find a way to generate violations of dymanic relationships that the human ear cares about which would not be detected with static THD or IMD. I'm not sure I'll ever get anywhere with it, but I can't help but feel curious about it.

All that wall of words, plus changing what I said, with a highly questionable assertion thrown in for flavor. But no actual examples or data.

 

[eboleyn]

All that wall of words, plus changing what I said, with a highly questionable assertion thrown in for flavor. But no actual examples or data.

It seems like you think I'm trying to attack you, which is not my intention. I'm also not sure how I was "changing what you said" per se.

As to the "highly questionable assertion", perhaps you're meaning the comment about being able to build a machine which can pass a static THD or IMD test easily but not be able to reproduce music well. We already see cases of existing audio chains that have "resonance peaks" which resist changing frequencies once driven, so suppose you built a machine which produced sets (say some limited number) of pure tones via pure tone generators, and only locked on to the tones over a period of time (enough to easily be perceptible to humans). It would likely pass a static THD or IMD test just fine. I would also agree it's pretty ridiculous, but in my meager defense of the example it's not too unlike some early audio hardware experiments that existed.

A reasonable argument is that my example is specifically tuned to defeat the test... but the point in the example is to find out if traditional THD/IMD measurement numbers can track correctness in full audio reproduction.

Perhaps your argument to me (as I am indeed the one less experienced in audio science) is that there is some proof that I am unaware of that IMD and THD measurements somehow cover all those cases and the machine I'm postulating wouldn't pass the test due to some failure of imagination on my part, to which I am happy to learn about, as I've not done any kind of thorough search of the literature.

It will probably take me a few days/a week-ish of evenings, but arguably it's on me to try to build at least an electronic simulation of my fake proposed machine, and I might do it for fun.

 

[dc655321]

We already see cases of existing audio chains that have "resonance peaks" which resist changing frequencies once driven

Can you provide examples of these cases please?

 

[SIY]

It seems like you think I'm trying to attack you, which is not my intention. I'm also not sure how I was "changing what you said" per se.

As to the "highly questionable assertion", perhaps you're meaning the comment about being able to build a machine which can pass a static THD or IMD test easily but not be able to reproduce music well. We already see cases of existing audio chains that have "resonance peaks" which resist changing frequencies once driven, so suppose you built a machine which produced sets (say some limited number) of pure tones via pure tone generators, and only locked on to the tones over a period of time (enough to easily be perceptible to humans). It would likely pass a static THD or IMD test just fine. I would also agree it's pretty ridiculous, but in my meager defense of the example it's not too unlike some early audio hardware experiments that existed.

A reasonable argument is that my example is specifically tuned to defeat the test... but the point in the example is to find out if traditional THD/IMD measurement numbers can track correctness in full audio reproduction.

Perhaps your argument to me (as I am indeed the one less experienced in audio science) is that there is some proof that I am unaware of that IMD and THD measurements somehow cover all those cases and the machine I'm postulating wouldn't pass the test due to some failure of imagination on my part, to which I am happy to learn about, as I've not done any kind of thorough search of the literature.

It will probably take me a few days/a week-ish of evenings, but arguably it's on me to try to build at least an electronic simulation of my fake proposed machine, and I might do it for fun.

And you continue. Please quote me accurately.

 

[pma]

This is to show that my "torture load" test circuit shown in post #1 is in a good conformance with valid standard to test power amplifiers.

 

[egellings]

Yes, not a pretty sight. Pretty much everything in the 1960s and 70s that came out of good old England was bandwidth limited. Darned Philips transistors.

Then came Japanese high speed silicon.

English F.R. curve looks like a frown; California F.R. curve looks like a smile.

 

[Scrappy]

Load-testing amps is a good bit of my workday. It’s a bank of big resistors, able to take 4000w. I test 3300w on modern amps, and 1600w on the old boys with 1k tone. Yea it’s just “resistive;” don’t care as it puts the output devices, and more importantly the PSU thru some strife. Can the PSU “suck in” ~25A for 30sec or so without fail? Good to go! Ha.

 

[pma]

This is to show that my "torture load" test circuit shown in post #1 is in a good conformance with valid standard to test power amplifiers.

I tried the test as in the picture, with C - R = 33uF + 2.5 ohm (just what I immediately had here). It seems interesting. By changing the resistor value we may affect the output impulse current, which has nature of square wave derivative, when I used the 1kHz square as a source. Changing the repetitive frequency will change the dissipated power. Looks like this:

Please note the current clipping and loss of FB function in the last X-Y plot.

 

[fpitas]

Can you provide examples of these cases please?

Yeah. I have no idea what that means.