John Curl's Blowtorch preamplifier part II - Page 2852 - diyAudio
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Old 27th October 2012, 01:03 AM   #28511
kevinkr is offline kevinkr  United States
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Originally Posted by janneman View Post
Except that the opamps all measured essentially the measurement floor. Even the lowly TL074. Low ol bandwidth, very high feedback factor, go figure.

jan
Measurement artifact?
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Old 27th October 2012, 02:13 AM   #28512
RNMarsh is offline RNMarsh  United States
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many opa are not symmetrical topologies. especially, the 'classic' opa design.
Your more likely to have these issues with such opa design topologies.

-Thx RNM
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Old 27th October 2012, 02:29 AM   #28513
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Quote:
Originally Posted by janneman View Post
Zero V DC. You need to have a small signal riding on the DC offset to be able to measure the phase shift.
Of course.

jan
Quote:
Originally Posted by kevinkr View Post
Phase shift is referred to changing levels of DC offset at the output. (Not changing levels of AC signal amplitude) This apparently is pretty typical behavior for op-amps operating on relatively low supply voltages, shifts internal operating points, etc. (Look at GBWP and phase margin at different supply voltages for a hint)
Thanks for the clarification and education, guys!
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Old 27th October 2012, 02:50 AM   #28514
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many opa are not symmetrical topologies. especially, the 'classic' opa design.
Your more likely to have these issues with such opa design topologies.
Not necessary. Phase modulation twice per period sounds nastier than once per period.
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Old 27th October 2012, 03:16 AM   #28515
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Originally Posted by RNMarsh View Post
Facinating! OMG. Maybe what M.Otala and JC etal has been talking about is true? And, what would that affect do to the clarity of the sound?

I wouldn't be surprised to find that this affect has also been heard and described by careful listeners without knowing what it was, exactly. And, why certain designs sound better and thus contributes to why JC does design the way he does? OMG.

But pease note:

"Except that the opamps all measured essentially the measurement floor. Even the lowly TL074. Low ol bandwidth, very high feedback factor, go figure."

Not exactly what JC believes, i.e. "op-amps, can't use 'em" so I would make exactly the opposite conclusion. Or OTOH go back to the old discussion about how the euphonic colorations make people prefer the less accurate amplifiers.
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Last edited by scott wurcer; 27th October 2012 at 03:20 AM.
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Old 27th October 2012, 03:20 AM   #28516
RNMarsh is offline RNMarsh  United States
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There's always a not necessarily. ??

A lot of opa topologies are quit asymmetrical in their topology designs. Again -- show great with symmetrical waveforms (sine waves). I'm not going back into - an FFT of anything is a bunch of sine waves discussion. Just note that amp circuits dont care about such subjects and work differently with signals which contain a dc component or average which is non-zero. Symmetrical/balanced topologies seem to work the best for audio. My instincts tell me this might be a factor in the authors results. Thx-RNM

Last edited by RNMarsh; 27th October 2012 at 03:27 AM.
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Old 27th October 2012, 03:27 AM   #28517
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I use IC's exclusively in the JC-3 phono preamp. It is just not as good as the Vendetta Research phono preamp or the new Constellation phono preamp that are made with discrete components.
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Old 27th October 2012, 03:29 AM   #28518
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Well Ron used all kinds of test signals, pulses, squarewaves with sines superimposed, etc. You really need to read the paper to appreciate his findings in all detail. But it has a couple of surprises.

jan
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Old 27th October 2012, 03:50 AM   #28519
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yep. various waveform shapes -- other than relying on symmetrical sine waves --- is the only way you'll find anything new. I look forward to reading it. And, his future follow-up work in sorting things out further. Then, I can comment in a more specific way. Thx-RNM
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Old 27th October 2012, 04:05 AM   #28520
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all of which brings me back to a distortion limiting parameter: common-mode rejection.... rejection of the dc component, as i call it, or the 'average' of a non-sine wave.
After all, that what CMR is about. [Something the FFT throws away (ignors), usually.]

We need to have DIY, SIM'ers and others maximize cmr also and not get tied only to thd and noise. If they want to hear great music at the highest level of performance.

How are opa used that compromise cmr? Might be a good point to start. Then, How does the cmr change with differing waveform shapes and differing topologies?

How much of the cm signal which is not rejected, can be turned into diff-mode and amp'ed? These things are not seen when sine waves of seperate, individual tests are done... they just look like spec numbers. CM to DM conversion probably happens a lot in audio systems.... even with opa that would otherwise measure super cmr on the bench.

Thx - RN

Last edited by RNMarsh; 27th October 2012 at 04:34 AM.
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