John Curl's Blowtorch preamplifier part II

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#28,541
Within an amplifier, every signal component frequency modulates every other by some (small) amount. We accept this easily for loudspeakers, and for a single full-range driver is very significant. A generic amplifier is also full range, but the magnitude of effects is still under discussion.

Thanks,
Chris
 
#28,543
RNMarsh said:
This is not even remotely close to what I am talking about.
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Mr. Marsh, have you got a method to get rid of
.. a distortion limiting parameter: common-mode rejection.... rejection of the dc component, as i call it, or the 'average' of a non-sine wave.
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which does not introduce phase shift?

The methods I'm aware of are either linear & minimum phase (ie as God intended) or non-linear. But even the evil DSP and non-linear methods introduce big phase shifts.

I apologise for inserting (pseudo?) guru microphone stuff into this thread.
 
#28,544
#28,547
scott wurcer said:
There is an element of the truely bizzare here, an extremely verbose recent patent application citing wow and flutter of cassette recorders and VCR's, I don't get it. I mean even AM radios have outlived cassettes in cars.
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I believe the attempt is made to distinguish similar techniques from his by virtue of their application. That is, he is not attempting to patent a wow and flutter meter as used for tape machines, or a system for characterizing chroma distortions in video, etc.

Not sure if the strategy is going to be productive.
 
#28,548
john curl said:
Yes, Ron is 'verbose'. He writes his own patents, how about you?
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Pro se patents are usually a bad thing, they might feel good at the time but one tends to be blind to how they actually work in favor of their "baby". Nothing worse that an inventor written patent coupled with a bad examiner, in fact someone was even able to re-patent the current feedback op-amp because he thought he invented it in 1992.

I have no interest is re-engaging on the PIM discussion, I would rather like to see clarification of Jan's observation. If Ron's test shows most modern op-amps to measure perfectly I would like to see you address that in light of past comments.

Who's The Devil in this discussion, does anyone know?
 
#28,550
john curl said:
Just came back from the AES. Met Ed Simon and Jan Didden there. Had a good time, but I am old, and I am glad to be back home. '-)
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Are you coming tomorrow to BAF John?

Edit: listening I Hear A Rhapsody, by Bill Evans & Jim Hall on Undercurrent. Nice music, but annoying rumble around 20 Hz. What is it? It is not stable, like modulated by amplitide by noise.
 
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#28,552
scott wurcer said:
I have no interest is re-engaging on the PIM discussion, I would rather like to see clarification of Jan's observation
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Wasn’t Mr. Cordell clear enough?

Bob Cordell said:
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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scott wurcer said:
Who's The Devil in this discussion, does anyone know?
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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
 
#28,553
PMA said:
Richard, audio signal is assymetric, I agree. But has zero dc component..
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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
 
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#28,554
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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#28,559
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. '-)
 
#28,560
RNMarsh said:
average (CM signal) is not zero in music but is zero with a sine wave.
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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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