Radio Shack Electronic Drums Schematic 60-2249

One more attempt to preserve and understand a drum circuit...
This time we have the Radio Shack Electronic Drums from some time in the 80s.
It features four velocity responsive drum pads, and four sounds. There sounds are bass, snare, tom tom, and phaser.

I took a few good picture of the board, front and back. Then I traced them in Gimp. I make layers for things like jumpers, components, holes, top/bottom copper, etc. I also color code things like power rails and audio buses. That makes it easy to view exactly what I need while creating the schematic.

Here's a rough copy of the board in Eagle. Some of the transistors didn't have equivalent footprints, so liberties were taken.

I recognized the configuration as a variation on the classic "Bridged-T" oscillator, or a damped tuned resonator. Three of the voices are basically the same, while the last is gated noise. Nothing terribly interesting, but here it is.

Eagle files and high resolution images available on my github.