Obsolescence of groovy synth parts

[jhaible]

> that the 741 still
> remains... dont flame me, Im all for it, if it works why mess with it?

No reason for flames at all. I think it's no problem to build a top quality
analogue synth just using discrete transistors and 741's.

I almost did this with my JH-4, and I don't see much reason why one would
want opamps in the signal path of a synth at all (other than emulating a
certain
behaviour of a commercial circuit, and for series production with minimum
adjustment and high integration density, of course).

In many cases a simple transistor pair is all that's needed where you
normally
have an OTA. Just think of two VCA stages in series: Why boost the signal
to your usual 10V "opamp levels", only to attenuate them again for the next
OTA input ? Calculate the collector resistors so that you have the right
level
for the next transistor pair, and you even have a balanced signal path,
avoiding
GND crosstalk if you have to cross some distance on the pcb.

Building *opamps* from discreet transistors is a bit tricky, at least for
me, because
I always run into stability problems or end up with low slew rate. (No beta
reduction techniques for discreete circuits ....) BUT you're much better off
if you don't use opamps in the signal path of a synth anyway, and not using
multi stage feedback at all. (The VCF being the only exception, naturally)

For control stuff, CV adders and so on, opamps are quite handy, but *there*
you can go very far just using 741s.

Now, don't flame *me* !

JH.