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John Curl's Blowtorch preamplifier part II
John Curl's Blowtorch preamplifier part II
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Old 7th April 2012, 01:32 AM   #22081
john curl is offline john curl  United States
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see what I mean?
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Old 7th April 2012, 01:54 AM   #22082
scott wurcer is offline scott wurcer  United States
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Quote:
Originally Posted by Bonsai View Post
LoL!
If we can't have a sense of humor around this stuff, why bother.
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Old 7th April 2012, 01:55 AM   #22083
john curl is offline john curl  United States
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another example
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Old 7th April 2012, 01:59 AM   #22084
john curl is offline john curl  United States
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The REAL question is: WHY do I design this way?
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"Condemnation without Examination is Prejudice"
 
Old 7th April 2012, 02:04 AM   #22085
elektroj is offline elektroj  Europe
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Quote:
Originally Posted by john curl View Post
see what I mean?
Rotate your "normal" schematic by 90 degrees and it gets scary. Who are your ancestors, John?
I am serious, by the way.

Last edited by elektroj; 7th April 2012 at 02:07 AM.
 
Old 7th April 2012, 02:29 AM   #22086
Chris Hornbeck is offline Chris Hornbeck  United States
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Here's an alternative to mirroring that maintains power supply immunity. Cascoding of the VAS is required for best performance.

Series differential VAS.jpg

Thanks,
Chris
 
Old 7th April 2012, 04:13 AM   #22087
wayne is offline wayne  United States
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John Curl's Blowtorch preamplifier part II
Quote:
Originally Posted by john curl View Post
The REAL question is: WHY do I design this way?
Because that circuit will work, sound good, measure well and still work in 15 years. Plus if the parts are Toshibas it will go up in value.
 
Old 7th April 2012, 05:24 AM   #22088
VladimirK is offline VladimirK  Uzbekistan
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Few days ago John mentioned importance of resistors used at NFB chain.
I did impedance measurements of some different type resistors, impedance behaviour above 100kHz is very specific for every individual resistor, and even below 100kHz some fluctuations of impedance modulus is observed (I'll post it late on). Another side of the story, what materials resistors are made of, and how "pure" manufacturing technology is.
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Old 7th April 2012, 09:24 AM   #22089
PMA is offline PMA  Europe
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Originally Posted by john curl View Post
another example
JC-2
 
Old 7th April 2012, 10:08 AM   #22090
VladimirK is offline VladimirK  Uzbekistan
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Here is the relative variation of the impedance modulus of various resistors with frequency. The vertical axis is |Z(f)| / |Z(200Hz)|, total span of the axis is +-2%.
Even at medium frequencies there are some ripples of impedance (possibly some electrostrictive deformation).
These results are taken at the same 1V RMS test sine signal. Impedance will also vary by the test signal amplitude variation. I am afraid to imagine what goes on with a given resistor when unstable schematics usually oscillate (10...100MHz).
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