John Curl's Blowtorch preamplifier part II - Page 3250 - diyAudio
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Old 10th January 2013, 08:54 PM   #32491
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Originally Posted by scott wurcer View Post
Think one frequency in the Fourier domain the derivative has both signs, but it makes no physical sense to subtract AND add resistance by constriction of path. So I see seconds, sort of a rectifying mechanism.
Bingo. That is why I mentioned ideal rectifiers needed in the simulation.

Scott...you have access to an AP?

jn
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Old 10th January 2013, 09:14 PM   #32492
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Originally Posted by jneutron View Post
Bingo. That is why I mentioned ideal rectifiers needed in the simulation.

Scott...you have access to an AP?

jn
Yes, but I don't know how to "drive" it.
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Old 10th January 2013, 09:25 PM   #32493
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We seem to be getting dangerously close to YAFD.
I try to understand this slang expression. Does-it has a connection with some sexual relationship with flies ?
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Last edited by Esperado; 10th January 2013 at 09:30 PM.
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Old 10th January 2013, 09:33 PM   #32494
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Originally Posted by scott wurcer View Post
What math? This circuit works as shown just fine a 65k FFT has about 1Hz noise BW and the distortion components are easily resolved. Ed the 1.5uV is also X101 to the output not just the noise. 1.5uV of thirds is 150uV at the output (that's the point of the circuit) the noise in a 1Hz BW is ~.27uV. I think Bob Pease included the pictures when he did it.
Scott,

The AP System 2 as mentioned in the documentation doesn't do 65k FFTs!

The signal output voltage is 5 volts! That is where the data sheet shows the lowest distortion. As I suspect you know the falling distortion curve is really just showing the drop in noise level. (S+N)/N Above 5 ish volts the distortion begins to rise.

The 1.50 uV is the .00003% of the 5 volts out or what is suposed to be the measured distortion. If you want try the calc with the .000009% distortion number that is .45 uV! The claimed distortion is, if not at the noise level, very very close.

Now from the data presented in the manufacturer's data sheet and simple calcs, my suspicion is that we really are seeing noise distorted data.

My point is that modern opamps have surpassed many passive components!

Scott just join George and I in a bottle of Ouzo, you'll feel better.
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Old 10th January 2013, 09:36 PM   #32495
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Originally Posted by jneutron
The answer is, it is a depiction of current crowding INDEPENDENT of the direction in which the current is changing.
The crowding depends only on frequency, not magnitude. Skin effect, and hence proximity effect, gives a geometric current pattern governed by frequency alone. Look at the maths in any decent EM textbook. That is why, as jcx(?) said, it can be modelled by adding some inductances to parallel paths.

Looking in the time domain, as you seem to be doing, will create complications when the phenomenon is best considered in the frequency domain. Of course the two must give the same results when done properly, but one will often be easier to deal with.

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Originally Posted by Esperado
I try to understand this slang expression.
YAFD is an FLA - four letter acronym - which I just invented. It means Yet Another Fourier Debate. A debate which I don't intend to repeat, as my experience is that Fourier deniers cannot be convinced of their error.

Last edited by DF96; 10th January 2013 at 09:38 PM. Reason: reply to Esperado
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Old 10th January 2013, 09:41 PM   #32496
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Originally Posted by john curl View Post
Back in 1974, we found BIG PROBLEMS with first rate potentiometers in regards to HARMONIC AND IM DISTORTION. Some of the most expensive and best known potentiometers suffered from this problem.
Allen Bradley and Waters were the first pots that I measured that were AUDIBLY bad, and had to be dealt with. Now, it is known that LOADING THE WIPER is usually a bad thing to do, but many of you here do it all the time with one project or another, and nobody warns you off.
It is true that some pot fabrications are more tolerant to loading than others. For example, both Penny & Giles and Alps are pretty good, even when loaded somewhat, Bourns and Clarostat is OK too.
However Allen Bradley and Waters were bad, at least the ones made 30 years ago, and still marginal without significant loading of the wiper. It was easily measured with a ST analyzer, and probably still is today.
When it comes to ABSOLUTE SOUND QUALITY, even static distortion measurements do not appear to tell everything, so for my VERY BEST EFFORTS, like the earlier JC-80 or the CTC Blowtorch, we used either P&G or TKD pots. They are more expensive, but they work better too. Let's hope we can end this confusion and learn something new.
Thanks for that comprehensive rundown on the comparative qualities of pots, John, that's the sort of info, gained from real experience, that's invaluable ...

Personally, I could not tolerate a system using a conventional pot for volume, except for a quick evaluation of capabilities ...

Frank
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Old 10th January 2013, 11:37 PM   #32497
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YAFD is an FLA - four letter acronym - which I just invented. It means Yet Another Fourier Debate.
Thanks for the explanation, DF96. I hated acronyms, but just invented acronyms, you can't imagine :-)

This said, you where not the first: Urban Dictionary: YAFD

IBIF.
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Personally, I could not tolerate a system using a conventional pot for volume, except for a quick evaluation of capabilities ...
Really ? Did-you buy your records on Mars ?
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Old 10th January 2013, 11:45 PM   #32498
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Scott,

The AP System 2 as mentioned in the documentation doesn't do 65k FFTs!

The signal output voltage is 5 volts! That is where the data sheet shows the lowest distortion. As I suspect you know the falling distortion curve is really just showing the drop in noise level. (S+N)/N Above 5 ish volts the distortion begins to rise.

The 1.50 uV is the .00003% of the 5 volts out or what is suposed to be the measured distortion. If you want try the calc with the .000009% distortion number that is .45 uV! The claimed distortion is, if not at the noise level, very very close.

Now from the data presented in the manufacturer's data sheet and simple calcs, my suspicion is that we really are seeing noise distorted data.

My point is that modern opamps have surpassed many passive components!

Scott just join George and I in a bottle of Ouzo, you'll feel better.
Sorry Ed you just obviously don't understand that circuit, you compute the resistors noise contribution (nil) and then say the resistors should be smaller.

Stop and think about it, the noise AT THE INPUT of the op-amp is 2.7nV/rt-Hz the distorton REFERED TO THE INPUT is 1.5uV they are BOTH amplified by 101, the distortion and noise of the souece see a gain of one. Trust me Ed you ARE wrong and I don't particularly like Ouzo or any pastis from any other culture.
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Old 11th January 2013, 12:15 AM   #32499
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- four letter acronym - are XTLA's
that's eXtended Three Letter Acronyms
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Old 11th January 2013, 12:16 AM   #32500
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Really ? Did-you buy your records on Mars ?
Yes, I know the "dilemma" - every recording has already gone through a series of pots back in the studio; therefore why should one extra on the preamp make such a difference?

Part of the answer is that the pot's in the studio generally have to be reasonably decent, robust units; they wouldn't last long in the industry if they were too obviously flaky; another is that these attenuators are constantly being adjusted during the recording session, the contact points are refreshed frequently during this time; also, the sound of the distortion artifacts are now part of the recording's tone, ambience, the feel of the event, subjectively they belong to what happened in the studio, not what is going on in your room; and, a major chunk seems to be that these sorts of problems are worse when reproducing via speakers rather than recording, the fact that much larger pulses of current flow with PAs in the picture exacerbates things.

That said, many recent classical recordings are very dodgy in SQ, track to track the variation in level of artifacts that I usually associate with volume controls is quite striking -- perhaps because the engineers are getting too sloppy ...

The biggest reason, though, is that I know that my volume control makes a difference, I can hear it -- I can't do anything about what's on the recording, but, I can do something about the gear in my room. Therefore, I do what's necessary to eliminate that "annoyance" ...

Frank

Last edited by fas42; 11th January 2013 at 12:18 AM.
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