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Old 27th October 2012, 11:34 PM   #28551
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Originally Posted by scott wurcer View Post
Who's The Devil in this discussion, does anyone know?
You, i presume.
With so little ego, you surely have something to hide.
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Old 27th October 2012, 11:36 PM   #28552
gpapag is offline gpapag  Greece
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Originally Posted by scott wurcer View Post
I have no interest is re-engaging on the PIM discussion, I would rather like to see clarification of Jan's observation
Wasn’t Mr. Cordell clear enough?

Quote:
Originally Posted by Bob Cordell View Post
Hi Jan,

Although I haven't seen Ron's paper, I'm really looking forward to seeing it.

I think the phase deviations you show here are probably fairly easy to explain. As the operating points change, the forward gain of the amplifier changes and the closed-loop bandwidth changes. A far-out change in the closed-loop bandwidth, often acting roughly like a single pole at the gain crossover frequency, will cause a change in phase shift at frequencies well below that crossover frequency. That is what causes PIM.

These operating point forward gain changes can occur due to numerous things happening, but at high frequencies one of them could be the voltage-dependency of junction capacitances.…

The idea of looking at phase lag as a function of a DC offset is largely the same as Matti Otala's original proposal for measuring PIM. That is, mix a 60Hz signal with a 6 kHz signal and look at the phase modulation on the 6kHz "carrier" after the test signal is passed through the amplifier under test. This is sort of like the SMPTE IM test, except that we look for phase modulation on the carrier instead of amplitude modulation (AIM). …
As long as we can argue that the 60Hz stimulus is low enough in frequency to look like a DC offset for purposes of measurement, the two approaches are essentially the same.


It is virtually impossible to have any significant amount of PIM without also having an easily measureable amount of THD-20, since the same nonlinearity that causes PIM will also cause HF THD.

Cheers,
Bob


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Originally Posted by scott wurcer View Post
Who's The Devil in this discussion, does anyone know?
I know of one Devil only

The Rolling Stones - Sympathy for the Devil (1969 Hyde Park Concert) - YouTube
Rolling Stones - Sympathy for The Devil ( Live 1969 Altamont - YouTube
The Rolling Stones - Sympathy For The Devil (Live) - OFFICIAL - YouTube
The Rolling Stones : Sympathy For The Devil (live) HQ - YouTube


George
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Old 28th October 2012, 12:07 AM   #28553
RNMarsh is offline RNMarsh  United States
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Richard, audio signal is assymetric, I agree. But has zero dc component..
Sorry to be mixing issues in unclear way - email short hand isnt good enough to make it clear in a short sentence -- The average (CM signal) is not zero in music but is zero with a sine wave. Got to think of the implications. I got to git out of here... they're coming for me soon to go to airport. Pls spend some time with sim on cmr of SW-OPA..... not just thd and noise. Later when we have one built on pcb we can measure the cmrr. Its an often over-look distortion source with audiophiles. xplore cmr as distortion creation with certain topologies. Thx-RNM

Last edited by RNMarsh; 28th October 2012 at 12:14 AM.
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Old 28th October 2012, 02:46 AM   #28554
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Only slightly OT:

Had a great day today at the AES, JC and ES came by!
Plus several others of course that had interesting or fascinating audio stories.
Looking forward to Burning Amp tomorrow!

The pic below, from R2L: ES, JC, yours truly.

jan
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Old 28th October 2012, 02:48 AM   #28555
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Quote:
Originally Posted by jan.didden View Post
Only slightly OT:

Had a great day today at the AES, JC and ES came by!
Plus several others of course that had interesting or fascinating audio stories.
Looking forward to Burning Amp tomorrow!

The pic below, from R2L: ES, JC, yours truly.
Does John wear Hi-End 3D glasses? I see something blue there...

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Old 28th October 2012, 02:54 AM   #28556
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I am blind in that eye, Wavebourn! That is why I cannot drive myself to burning amp. Just too far, just too dangerous.

Last edited by john curl; 28th October 2012 at 03:00 AM.
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Old 28th October 2012, 03:09 AM   #28557
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Originally Posted by john curl View Post
I am blind in that eye, Wavebourn! That is why I cannot drive myself to burning amp. Just too far, just too dangerous.
Sorry John! I did not know that, I thought it is some reflection from some stand.

I go tomorrow morning, I can take you. Is it Alcatraz street?
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Old 28th October 2012, 03:35 AM   #28558
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Anatolyi, if you could do that, that would be great!
If John agrees of course, and has a way to get back home at some time.

jan
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Old 28th October 2012, 04:22 AM   #28559
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Thanks for the offer, Wavebourn, but Jan is right, and I have a limited capacity for such doings. I only lasted till 1:00 today, maybe 3 hours, and I was ready to go home. It is just too uncomfortable to hang around such events. But thanks again, for your offer, enjoy yourself. '-)
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Old 28th October 2012, 04:23 AM   #28560
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Quote:
Originally Posted by RNMarsh View Post
average (CM signal) is not zero in music but is zero with a sine wave.
What is a common mode for an audio signal? Do you mean an amplifier connected for non-inverting gain. Common mode and DC for air pressure as it relates to the propagation of waves doesn't make much sense. I suppose popping a balloon in a sealed room would leave a change of DC pressure.

The statement that AC coupled asymmetric waveforms have a net DC component keeps coming up like it's a fact.
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