I was able to get another obscure drum machine, an Electro Harmonix Rhythm 12.
It has a somewhat unique sound, and I wanted to understand the voices better. There is a schematic available out there, but it's not the clearest. As usual, I decided to redraw it in Eagle CAD.
There are basically 4 voices, but they can be manipulated a bit. Parts of the sounds can be muted or even cut short.
Here is the portion that actually creates the sound. The sequencing and amplification parts are not shown.
There are four "Twin-T" oscillators present. Three are damped, so that they decay naturally. One is self oscillating, and generates a tone used in the cymbal.
The cymbal and snare noise go through single transistor VCAs. These are pretty crude, and seem to work by offsetting the input into (and out of) the active region of the transistor. This heavily distorts the signal, but it does work.
Most of the other transistor serve to mute drums for pattern variations.