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

[René Schmitz]

At 14:10 30.06.00 +0200, Haible Juergen wrote:

>Bottom line for *me* is that until I see any groundbreaking article
>on that subject, I'm either using integrated opamps, or
>(and with increasing pleasure) discrete circuits that don't use
>multi stage feedback at all. It's astounding how many 
>functions in a synth do not need the opamp circuit topology
>(integrated or discrete) at all. 

100% agreed. I'd even go one step further: The complete audio path can be
done without negative feedback. (And hence no compensation.) 

The FET circuits we've seen lately were mostly not feedback (at least not
over several stages), but still have very small THD. Devices with a square
law characteristic (triodes, FETs) allow it to cancel most of the even
order harmonics by symmetrical or push pull arrangements. And these devices
generate only smaller ammounts of odd order distortion, compared to the
exponential law for BJTs. 

IMO much of the "transparency" and "resolution" that is attributed by
audiophile circles to these kind of circuits has to do with the absence of
multi stage feedback.

Bye,
 René
-- 
uzs159 at uni-bonn.de
http://www.uni-bonn.de/~uzs159