John Curl's Blowtorch preamplifier part II - Page 3250 - diyAudio
 John Curl's Blowtorch preamplifier part II
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diyAudio Member

Join Date: Jan 2004
Location: away
Quote:
 Originally Posted by scott wurcer 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.

jn

diyAudio Member

Join Date: Jan 2004
Location: dorchester ma
Quote:
 Originally Posted by jneutron 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.
__________________
"The question of who is right and who is wrong has seemed to me always too small to be worth a moment's thought, while the question of what is right and what is wrong has seemed all-important."

Banned

Join Date: Jul 2011
Location: Portugal
Quote:
 Originally Posted by DF96 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 ?

Last edited by Esperado; 10th January 2013 at 09:30 PM.

diyAudio Member

Join Date: Nov 2008
Location: Oakmont PA
Quote:
 Originally Posted by scott wurcer 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.

diyAudio Member

Join Date: May 2007
Quote:
 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.

Quote:
 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

Banned

Join Date: Jun 2012
Location: NSW, Australia
Blog Entries: 13
Quote:
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

Banned

Join Date: Jul 2011
Location: Portugal
Quote:
 Originally Posted by DF96 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.
Quote:
 Originally Posted by fas42 Personally, I could not tolerate a system using a conventional pot for volume, except for a quick evaluation of capabilities ...

diyAudio Member

Join Date: Jan 2004
Location: dorchester ma
Quote:
 Originally Posted by simon7000 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.
__________________
"The question of who is right and who is wrong has seemed to me always too small to be worth a moment's thought, while the question of what is right and what is wrong has seemed all-important."

 11th January 2013, 12:15 AM #32499 diyAudio Member     Join Date: Sep 2002 Location: Lakewood, Ohio - four letter acronym - are XTLA's that's eXtended Three Letter Acronyms __________________ Kevin
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Join Date: Jun 2012
Location: NSW, Australia
Blog Entries: 13
Quote:
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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