[sdiy] OT What David's up to (was Re: very simple VCA circuit)

[David G. Dixon]

> So you're building an analogue implementation of the Casio VZ synth voice?
> Each of 8 VCOs has a VCA controlling it's level, and you're going to add
> eight envelopes to complete the "operators"?
> 
> Or it's a Rave-o-matic SuperSaw generator, with multiple ramp VCOs with
> randomly controlled amplitudes?
> 
> Sheesh, I dunno - what ARE you up to?



No, it's nothing that elaborate, just a 2164 Expo VCO with a triangle core
based on a little known oscillator circuit (which I just happened to stumble
upon whilst thumbing through an old and otherwise quite unremarkable
textbook, and which I've seen nowhere else) which is perfectly suited to
2164 but which simply would not work with the standard OTA-based tricore.

Two of the 2164 VCAs constitute the temperature-compensated expo converter,
four comprise two linearized VCAs in a variably-balanced modulator (much
like the core of my 2164 Multiplying Modulator, a.k.a. the Intellijel uMod)
which controls feedback in the triangle core, and the last two constitute a
third linearized VCA which controls the amount of linear FM.

When I'm done, I should have a VCO which tracks well over 8 octaves, with
the same TZFM capability as the Zeroscillator, but with low parts count and
nothing exotic; just TL07x's, a couple of LM311's, a couple of 2164's, and
one or two BJTs and JFETs here and there.  I'll keep y'all posted.