John Curl's Blowtorch preamplifier part II
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 27th October 2012, 12:12 AM #28501 jan.didden   diyAudio Member     Join Date: May 2002 Location: Westende Resort, BE coast Actually in a way that phase modulation is quite easy to measure for all of us: Measure the phase shift between input and output with zero Vout. Then insert a DC offset of a few volts, and again measure it; you'll find it most probably has changed. One typical table from his paper: DC offset at the output Phase shift @ 15kHz -2V -25 degr -1V -24 degr 0V -23 degr +1V -22 degr +2V -21 degr So there's you varying phase shift with output level. Fascinating, isn't it? jan
SY
diyAudio Moderator Emeritus

Join Date: Oct 2002
Location: Chicagoland
Quote:
 Originally Posted by janneman Measure the phase shift between input and output with zero Vout.
How do you accomplish that at zero volts out?
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 27th October 2012, 12:22 AM #28503 Joachim Gerhard   diyAudio Member     Join Date: Mar 2009 Nothing is new under the sun. ( King Salomon )
 27th October 2012, 12:39 AM #28504 Wavebourn   diyAudio Member     Join Date: Sep 2006 Location: Pleasant Hill, CA Jan; I can tel you the similar way to catch a mice. When it is under the stool take a saw and quickly cut stool's legs. 1. Cut the 1'st leg 0.5 centimeters 2. Cut the 2'nd leg 0.5 centimeters ... 5. Go to 1 and repeat until the space is too small for the mice to escape. __________________ !!!Warning!!! Single Ended Class-A-Holism is addictive!!!
31697B
Account disabled at member's request

Join Date: May 2012
Quote:
 Originally Posted by janneman One typical table from his paper: DC offset at the output Phase shift @ 15kHz -2V -25 degr -1V -24 degr 0V -23 degr +1V -22 degr +2V -21 degr So there's your varying phase shift with output level. Fascinating, isn't it? jan
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.

 27th October 2012, 12:50 AM #28506 Wavebourn   diyAudio Member     Join Date: Sep 2006 Location: Pleasant Hill, CA What is fascinating? Did you hear SSB station on AM radio? How does it sound? Similarly, very small amount of phase intermodulation causes "harsh" highs and fuzzed stereo image. It's one of reasons why measurements of THD and IMD don't tell how good will be the sound. __________________ !!!Warning!!! Single Ended Class-A-Holism is addictive!!!
kevinkr
diyAudio Moderator

Join Date: Sep 2004
Location: Boston, Massachusetts
Quote:
 Originally Posted by SY How do you accomplish that at zero volts out?
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)
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jan.didden
diyAudio Member

Join Date: May 2002
Location: Westende Resort, BE coast
Quote:
 Originally Posted by SY How do you accomplish that at zero volts out?
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

jan.didden
diyAudio Member

Join Date: May 2002
Location: Westende Resort, BE coast
Quote:
 Originally Posted by kevinkr 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 GBP at different supply voltages)
Except that the opamps all measured essentially the measurement floor. Even the lowly TL074. Low ol bandwidth, very high feedback factor, go figure.

jan

jan.didden
diyAudio Member

Join Date: May 2002
Location: Westende Resort, BE coast
Quote:
 Originally Posted by RNMarsh 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.
Ohh yes of course it is true.
But not where we thought it was.

jan

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