John Curl's Blowtorch preamplifier part II - Page 2853 - diyAudio
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Old 27th October 2012, 05:33 AM   #28521
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Originally Posted by RNMarsh View Post
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.
Actually that's called AC coupling or LF roll-off.

Any LF roll-off introduces phase shifts, some of which can be heard in some circumstances. You MUST do this is any velocity (cardioid type or fig-8) microphone unless you are into recording air-conditioning, underground trains, distant thunder or want extra use as a seismograph .. ie bad sound.

There's a huge thread on gearslutz purporting to compare ADC/DACs which pans some converters based on their funny waveform response when really all that is showing is different LF response.
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Old 27th October 2012, 06:05 AM   #28522
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From omni mikes you are getting even more of rumble than from pressure-gradient mikes. But how is it related to CMRR? I see no connection.
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Old 27th October 2012, 06:27 AM   #28523
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Originally Posted by Wavebourn View Post
From omni mikes you are getting even more of rumble than from pressure-gradient mikes.
Not true. I pontificate at length on this subject on the Yahoo MicBuilders group for those who are interested.

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But how is it related to CMRR? I see no connection.
Just pointing out that what Mr. Marsh wants isn't CMRR but LF roll-off. ... though CMRR is important too.
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Old 27th October 2012, 09:02 AM   #28524
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Originally Posted by janneman View Post
Actually in a way that phase modulation is quite easy to measure for all of us:
-2V -25 degr
-1V -24 degr
0V -23 degr
+1V -22 degr
+2V -21 degr
Then insert a DC offset of a few volts, and again measure it; you'll find it most probably has changed.
I am not sure to understand.
Did-you say that the transmission "delay" on any signal change (may decrease) on those slow amps, according to the signal level ?
If so, you can measure the distortion, and, on square waves from -2 to +2v, see strange slopes where the top of the signal arrive before it starts (witch is impossible) ?
Or is-it something witch is not "time" correlated (delay change slowly according to the average level of the signal) ?

Pure curiosity, as i use exclusively current feed-back for audio since decades, with so high slew rates...
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Last edited by Esperado; 27th October 2012 at 09:19 AM.
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Old 27th October 2012, 09:31 AM   #28525
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My last question is confused on purpose, we all know that the slope of a square signal is never linear near the rails.
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Old 27th October 2012, 09:43 AM   #28526
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Quote:
Originally Posted by kgrlee View Post
Actually that's called AC coupling or LF roll-off.

Any LF roll-off introduces phase shifts, some of which can be heard in some circumstances. You MUST do this is any velocity (cardioid type or fig-8) microphone unless you are into recording air-conditioning, underground trains, distant thunder or want extra use as a seismograph .. ie bad sound.

There's a huge thread on gearslutz purporting to compare ADC/DACs which pans some converters based on their funny waveform response when really all that is showing is different LF response.
This is not even remotely close to what I am talking about.
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Old 27th October 2012, 10:26 AM   #28527
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I am unable to find the paper being presented at this months AES. Pls give exact info... type of paper, author name and paper title. The number 8722 did not bring it up. Thx RNM
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Old 27th October 2012, 10:38 AM   #28528
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Our ears are horns, and its membrane is not symmetrical at all. They produce their own distortion .(Mostly H2, while cones are H3)

I believe that, in a home system, distortion produced by a good horn/driver, is near the one of the ears, in regard to SPL. On a similar nature. I believe my brain interpret the driver's distortion as "level".
It don't bores-me at all.
May-be just the feeling that my system is slightly louder than measure would show... ?
The explanation about the fact i never notice those distortion i can measure, never feel-them as unnatural ?

I noticed, that, in PA, at big distance from the stage, the distortion is so high, and acoustic level so low that this distortion is disagreeable. If you go near the stage, where SPL is very high, you are not bored anymore by those.

Thinking about horns and cones, in our reptilian brains, we associate horns for PA, and cones for home (apart J.C.:-).
May-be all wrong ?
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Old 27th October 2012, 10:45 AM   #28529
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In regards to PIM etal --- While waiting to read R.Quan's paper --How would an amp get dc offset to show phase change.
I am suggesting it is thru the asymmetrical waveforms' CM signal component and how that CM signal affects the amp topology. [note that the CM component is zero in a sine wave...it is the average level in an asymmetrical waveform] I brought this up to JC decades ago.... after publishing a paper on Common-mode signals. However, I didnt relate it to PIM directly. Thx -RNM

Last edited by RNMarsh; 27th October 2012 at 11:08 AM.
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Old 27th October 2012, 11:02 AM   #28530
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Originally Posted by RNMarsh View Post
In regards to PIM etal
I'm very curious to see this paper too. As i know, phases turns are just a consequence of delays, in regard to frequency.
What the hell can we discover that a square wave signal don't show ?
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