I finally did it, after months of having my 707 open in the garage. I had made a
prototype 555 oscillator, which I tested by applying to the various gate pins.
Last weekend I made a small circuit board of eight such oscillators.

This morning I put 100k sealed 1/8" pots along the front of the unit, just in front
of the drum buttons. I lifted all of the relevant gate IC pins and severed the
traces under those. Severing the traces in front of the IC was easy. Soldering
the pins back onto their pads provided some mechanical support.
Unfortunately, pin 64 - handclap - had broken off of the Gate Array since I'd
last tried this a couple of weeks ago. I used a razor to gently scrape away
enough of the plastic on the chip to reveal a tiny bit of metal to solder to. I
connected the pots to the oscillator board, and ran outputs from it to the Gate
Array IC. The outputs were a little tricky, but no so bad. I used wire-wrap wire,
which must be like 30-32 AWG. Very fine stuff.

Having gotten all of the pins wired to their oscillators, the 707 does not work
quite as I had expected. There is some high-frequency noise from the 555s,
but that doesn't bother me. My kicks and snares sound nowhere near as good
as before I hard wired them. The toms are so loud now that they overwhelm
all of the other sounds. I put TWO clock signals to the kick or snare pins and
they sound great! I guess I will experiment with the resistor and cap values on
the oscillator board a little more. Somehow, the process of soldering the clock
outputs had caused the memory of the 707 to be filled with random drum
patterns! I spent a few hours exporing the new sounds with these ghost
patterns.

Overall sounds great, though I am going to need to tweak the setup a bit more
before I consider it ready.

CJ