[sdiy] Oberheim OB-Mx schematics and ROM dumps now up

[JH.]

> Oddly enough, it's the OB-Mx that started my interest in the subtleties of
> analog design, eventually leading to me joining this list, and eventually
> leading to me doing the synth special topics class I'm doing now. Everyone
> complained about the sound of the filters on the OB-Mx - but as you see
> that really is a transistor ladder, and it really is a state variable
> filter - the one unique thing is the use of SSM2024s all over the design.
> I got to wondering why some filters sound different than others, which
> lead me to wondering, which lead me to wondering...

The 2024 was a great little VCA, IMO.
As far as I understood it, it was real, non-linearised OTAs (no Gilbert, no
Blackmer tricks) just like the 3080, only built from much better
transistors.

I may be wrong - haven't seen the internal circuit - but the 10mV operating
level at the inputs clearly points into that direction, IMO.

JH.