NFB and Electron Propagation (from Blind Testing)

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#41
Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Harold S. Black.

Steve Eddy said:


If that were the case, then propagation velocity would have to be infinte. And propagation velocity is not infinite. You apply an "EMF" at one end of the line and the electrons at the other end of the line won't "experience" it until some time later.

More germane, the "EMF" at the output of the amplifier takes a certain, non-zero amount of time to propagate from the output back to the input. That time being the propagation velocity divided by the length of the feedback loop.

Which means that feedback is ALWAYS delayed by some amount.

se
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....'propagate' does not come into it......read last ref. carefully...i guess we'll have to agree to disagree...
 
#42
The electron stuff is hilarious; maybe if everyone defines the model system they're talking about with more precision and detail, the answers will be more obvious- like that you may be arguing apples and oranges.

And if retrospective feedback doesn't work, you'd better not drive your car. Or fly an F117.

nw, I can't say I feel more "relaxed" since spending some time running controlled listening tests, it's just that I have different reasons now for building tube stuff. And I have a different set of priorities in deciding where to focus my time, energy, and resources.
 
#43
Apples And Oranges.

Hi,

And if retrospective feedback doesn't work, you'd better not drive your car. Or fly an F117.
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Does that have anything to do with it?

Our entire body, every move we make depends on feedback...
However when it comes to the reproduction of music I would not use it carelessly.

In other words, yes feedback works. Is it perfect?
No, don't think so. Are all feedback circuits alike? No, they're not.
As SE pointed out, it is indeed best practice to:
a) keep the loop as short as possible.
b) (my words not his) better address it locally than globally.

Once again, it is a design choice that comes at a penalty it doesn't get rid of the problem, it lessens the effects of the problem.
So why not avoid the problem in the first place?

Cheers,😉
 
#44
Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Re: Harold S. Black.

mikek said:
....'propagate' does not come into it......read last ref. carefully...i guess we'll have to agree to disagree...
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Propagation absolutely does come into it. Any time a signal is transmitted any length there is propagation involved. And I did read that last reference carefully. It's just a simple piece on electron drift velocity, which is not the same as propagation velocity.

You can stop here and agree to disagree or you can learn something. Your choice.

se
 
#45
SY said:
The electron stuff is hilarious; maybe if everyone defines the model system they're talking about with more precision and detail, the answers will be more obvious- like that you may be arguing apples and oranges.
Click to expand...

I don't think it's a problem of which model is used (the classical model is fine for this and easier for most to understand) but rather mikek's only focusing on a singular flyspeck without considering the other elements involved in carrying signals from point A to point B.

Until he stops focusing on the electrons themselves, he ain't never gonna get it.

se
 
#46
se, it might help to specify things a little better; you know, what chunk of matter you're talking about, how you're connected to it, and what the signal looks like. There are a variety of valid ways to look at a system, but I think it's best to completely describe the system before you decide what's the most useful view. Just looking at all the water pipe stuff didn't give me a clue, nor do I have one now, on what system you guys are talking about if indeed it's the same one for all of you. I put this question to you because I give you the highest probability of being able to put it in terms I can understand.

Frequency Response changes per se, but more so due to fine changes in spectral/impulse response
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These are the same thing, Eric.
 
#47
SY said:
se, it might help to specify things a little better; you know, what chunk of matter you're talking about, how you're connected to it, and what the signal looks like. There are a variety of valid ways to look at a system, but I think it's best to completely describe the system before you decide what's the most useful view. Just looking at all the water pipe stuff didn't give me a clue, nor do I have one now, on what system you guys are talking about if indeed it's the same one for all of you. I put this question to you because I give you the highest probability of being able to put it in terms I can understand.
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It's really pretty simple.

We're talking about the negative feedback path in a realworld amplifier. So we're essentially talking about a transmission line of a non-zero length.

mikek originally said that there can be no delay in the feedback path. I pointed out that because electromagnetic waves propagate at a finite velocity, and the feedback path has a non-zero length, there will always be some amount of delay between the amplifier's output and the feedback port at its input.

mikek argued that the input sees the fed back output instantaneously and then gave his erroneous water analogy (it wasn't the analogy with water that was wrong but rather his assumptions as to the general behavior) to "prove" his claim that the input instantaneously sees the output.

So really what it boils down to is that mikek is saying that electromagnetic waves propagate with infinite velocity and therefore the input instantaneously sees the output and I've been trying to explain to him that this is impossible.

The delay will be so microscopically small that for all intents and purposes it can be ignored, but the delay exists just the same.

Up to speed now?

se
 
#49
Well, if that's all it is, then it's a pretty simple matter to hook a two channel high speed scope to the input and the output of an amp and prove to onesself that there IS a finite propagation time for an impulse signal. And that the DUT is dispersive. And that propagation time is, correcting for the minimum phase characteristic of the amp's HF rolloffs, pretty damn close to zero for those slow, molasses-like audio signals.

I make my engineers learn a set of laws, "SY's Laws." None are original, but I think all are useful so they have to memorize them, bark them back at me when challenged, and show me how they used them in a given real-world problem. They hate me. Anyway, SY's Second Law is, "Stop speculating and do the $&@%ing experiment." At least one of you guys has to have a high speed scope and pulse generator.
 
#51
SY said:
Well, if that's all it is, then it's a pretty simple matter to hook a two channel high speed scope to the input and the output of an amp and prove to onesself that there IS a finite propagation time for an impulse signal. And that the DUT is dispersive. And that propagation time is, correcting for the minimum phase characteristic of the amp's HF rolloffs, pretty damn close to zero for those slow, molasses-like audio signals.

I make my engineers learn a set of laws, "SY's Laws." None are original, but I think all are useful so they have to memorize them, bark them back at me when challenged, and show me how they used them in a given real-world problem. They hate me. Anyway, SY's Second Law is, "Stop speculating and do the $&@%ing experiment." At least one of you guys has to have a high speed scope and pulse generator.
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Eh? You mean there's some doubt that electromagnetic waves propagate at finite velocities?

se
 
#54
Re: RE:Up to speed now?

fdegrove said:
Yup, but audible nonetheless...and there nonetheless...and not to be neglected nonethess...
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Yeah? When was audibility established?

Let's see, given a rather worst case scenario with a propagation velocity of 0.6 C and a loop length of 0.25 meters, you're talking about a delay of...

0.0000000014 seconds, or 1.4 nanoseconds.

Tell me, what is the actual effect of such a delay on the output signal? In other words, what is the actual change made to the output signal compared to the input signal?

se
 
#56
SY said:
No, not at all; it's just that there comes a point when it's easier to acquire and post a simple waveform pair than to argue about the theory. That settles the argument rather quickly, nicht wahr?
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Well, if it's simply a matter of getting a correct answer, yeah, that works. But simply being shown a correct answer does nothing to increase your knowledge and understanding.

I mean, you can press the "7," the "X," the "6," and the "=" keys on a calculator and come up with "42," but if you don't understand the underlying concept of multiplication, while you have an answer, you don't understand any more about the underlying concept of multiplication than you did before.

By the same token, I could tell mikek that I'm right, he's wrong, throw up a 'scope photo and put another notch in my pistol grip, but what would that serve except perhaps to stroke my own ego?

I don't want mikek to just give in and concede. I want him to go "AH! I see!" It's one thing to know you're wrong. Quite another to know WHY you're wrong. When you understand WHY you're wrong, then you have truly learned something.

se
 
#57
delay...

fdegrove said:
Yup, but audible nonetheless...and there nonetheless...and not to be neglected nonethess...
Click to expand...

To paraphrase a a movie title, "Past back to the Future"


Steve Eddy said:
0.0000000014 seconds, or 1.4 nanoseconds
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and with a music signal, unlike a sin wave you can be pretty sure that what it is mixing it up with is not the same thing that passed thru 1.4 ns earlier (did you include the delay thru the active device?).

dave
 
#58
Re: LISTENING TO NUMBERS.

fdegrove said:
Having ourselves a problem or what?

I'm rather lost at your question Steve, care to 'splain it?...Slowly please... not at electron speed.
Click to expand...

Sure...

Frank...

Is...

This...

Slow...

Enough...?

It's simple.

You said that delay in the feedback loop on the order of nanoseconds was audible.

This is an objective claim.

And being an objective claim, in order for it to be a valid claim, there must be some objective evidence to subtantiate it.

So what I'm asking is, what objective evidence has established that nanosecond delays in the feedback loop are audible?

If there is no objective evidence to substantiate it, then it is nothing but opinion and should not be put forth as an objective claim.

Any objections?

se
 
#60
Giving it a rest

Steve Eddy said:
Eh? You mean there's some doubt that electromagnetic waves propagate at finite velocities?
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Well folks, the majority of the last few pages have been spent debating something that even the folks aruging agree doesn't have anything to do with the sound of an amplifier. It would seem the blind/null thread is played out for the time being at least.

I would think trying to measure a 1.4 nanosecond delay through something (an audio amp) that likely has a rise time roughly 1000 times slower that that, should be an interesting exercise.

I hope some of you got something out of the blind/null discussions and will perhaps be encouraged to try some blind and/or null testing of your own. I'm going to take fdegrove's advice and give it a rest for now.

Have fun everyone.
 
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