Compensating multi-stage feedback (was: RE: all tranny vca+ )

[Don Tillman]

   Date: Sun, 02 Jul 2000 15:14:40 +0200
   From: Magnus Danielson <cfmd at swipnet.se>

   Certainly, but now comes my key question:
   Are you sure that what you perceive is due to types of distorsion?
   Are you _really_ sure?

Pretty sure.  Anything's possible, but in the case of the mixers
the signal isn't going through a very complicated circuit and that
circuit isn't supposed to be doing anything exotic to the signal.

   My point is, I do not object to people hearing something sounding
   good or bad, but what I have learned is that very few people are
   able to pinpoint the correct process of destruction or enhancement
   (as below). 

Ahh, I know what you mean.  I'm pretty good at picking these out
though.  This particular "distortion" has a sound that's very
distinctive, very constistant and is fairly obvious.

   > Other classic examples are the Pioneer and Technics hifi
   > receivers from the mid-70's distortion spec race.  

   Well, was the measurement applicable to the process of destruction?

Certainly not, and that's the point.  Pioneeer and the others changed
the goal from making a great sounding amp to making an amp that tested
great on this one standardized measurement.  And this pointed out in
very clear terms the uselessness of this particular standarized
measurement.

   Now, to summerize what I have heard and what I know of which may
   destroy or enhance sound:

   Linear filtering
   Impulse responce (_should_ be the result of linear filtering)
   Cross-over distorsion (small signal distorsion)
   Linearity (medium signal distorsion)
   Clipp and clipp behaviour (large signal distorsion)
   Feedback loop behaviour on distorsion
   Amplifier load impedance behaviour
   RF intermodulation (any non-linear section will act as a mixer)
   Noise and noise modulation
   Cross-talk

Good list!  Here are my contributions:

Effects of junction capacitance varying with signal voltage
Power supply interaction
Effects of bias changes changes with waveform transients

Hey this is fun!

  -- Don

-- 
Don Tillman
Palo Alto, California, USA
don at till.com
http://www.till.com