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

[Harry Bissell]

OK I'll play too...

The op-amp cannot supply the negative feedback instantly... the more stages it
has internally, the longer the delay between giving it an input, and getting an
output. If you hit
it will a really fast rise-time wave... the input will not receive the feedback
for a while... which will make the output overshoot and/or make the other
internal op-amp stages do funny things during the overload...  Some opamps will
stick to the rail, or reverse direction
during this time...

OTOH for most synth waveforms... opamps are no problem.  You can tell the
distortion
on (lets say) a flute (if you KNOW what a flute is supposed to sound like...)
but can you tell the distortion on a squarewave, which is inherently "distorted"
already ???

I think (flamesuit ON) very few of the people in the world can hear the
distortion in an audio system unless it is GROSS.  Usually the speakers are far
worse than anything else
in the audio path!  And those few 'audiophiles'  (think
pedophile....necrophile...) that "could" hear the difference are probably so old
they cant hear over 12-15KHz anyway.

In fact... (shit)   FLAMESUIT OFF.... and I repeat that statement. !!!

(oh boy this is gonna be great !!!)

H^) harry

"J. Larry Hendry" wrote:

> OK, I am new to this game and have read this discussion with interest.  I
> will have to claim that I was totally ignorant to the use of op amps until a
> few months ago.  Now, I know just enough to make some op amp circuits work.
> I have a couple  of references that I am using on the subject.  1 - the
> simple Radio Shack booklet and 2 - the very in depth "Art of Electronics"  I
> have built a few of these circuits for summing and inverting and have the
> basic hang of it.
>
> What is escaping me here is why the use of an op amp and negative feedback
> in the audio path is perceived by some to be a bad thing.  For example, if I
> wanted to boost the level of a line level audio signal to use in my higher
> voltage modular audio path, seems like a simple op amp (one with the right
> characteristics for audio) would be easy choice.
>
> Without starting a discrete vs. op amp vs. tube all out onslaught, I would
> appreciate hearing individual reasons why one would choose to build a
> discrete circuit in the audio path as opposed to a good op amp.  Subjective
> reasoning is really what I am after.
>
> As always, thanks.  I don't post much here as my knowledge level is so far
> below the qualified ones on this list.  But, I read almost all of it and
> appreciate the great spirit of sharing.
>
> Larry Hendry
>
> ----- Original Message -----
> >100% agreed. I'd even go one step further: The complete audio path can be
> >done without negative feedback. (And hence no compensation.)
>
> From: jhaible <jhaible at debitel.net>
> That's what I intended to say. Been there, done that - the audio path of my
> JH-4 synth is completely built that way. The only multi stage feedback loop
> is in the VCFs, to get resonance.