John Curl's Blowtorch preamplifier part II

[john curl]

see what I mean?

[scott wurcer]

Originally Posted by Bonsai

LoL!

If we can't have a sense of humor around this stuff, why bother.

[john curl]

another example

[john curl]

The REAL question is: WHY do I design this way?

[elektroj]

Originally Posted by john curl

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.

[Chris Hornbeck]

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

[wayne]

Originally Posted by john curl

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.

[VladimirK]

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.

[PMA]

Originally Posted by john curl

another example

JC-2

[VladimirK]

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).