This is my gradual project.
I bought a DR110 off some d00d for a few dollars, it had some problems. The
edit screen was flaky, certain voice data blinking on and off. More to my
concern, the open hats, closed hats, and cymbals were not working. Since all
three of these sounds derive from a common source of filtered digital noise, I
poked around there. Noise chips worked, output all of the way... Near the
transistors where the brass envelopes are supposed to happen, I narrowed it
down to an electrolytic capacitor. It had been squezzed in a bad way, which
had pulled one of it's legs, and the solder pad, off of the board. I repaired the
trace with some fine wire, which I wrapped around the capacitor lead, and
thunderbirds are go! All drum voices work. But the display was cracked, so it
crubled off- too bad.

I love the sounds of the DR110. The noise source is filtered in just such a way
for the brass timbres, which is explained in detail in the DR110 service notes.
The claps, rimshot, kick, and snare are pure analog transistor badness.
Transistors are used to make analog envelopes for the hybrid brass sounds,
not unlike the voices in the TR-707. Kind of harsh, electro sounding, and
extremely moddable.

Now, the 707 is my favorite "grid" style drum sequencer interface. "X0X" at it's
best.- but I have never like the drum samples in the unit. I guess the toms are
decent, but on the whole the sounds are lacking. Never played with a 727, but
I should. Great interface though!

The DR110 is so small, that I can fit it's boards under the 707 circuits. What I
am trying to do is extract triggers from the 707 envelope circuitry, pretty
straightforward. Use those triggers to fire the 110 sounds, run the DR110
output up to the drum volume sliders, and use toggle switches to select 707 or
110 sounds. Since some of the sounds expect triggers with different timing, in
relation to each other (especially the handclaps), I think I will include the cpu
board as well as the voicing board. I wouldn't mind learning to use a
microcontroller for this, but neither have nor afford right now.

I have tried using a circuit which I had built, which turns input into +5v, 1ms
pulses, to inject working triggers into the DR110. No success. I know which
transistors expect triggers from the onboard CPU, but they don't fire voices
when I trigger them manually. Since the triggers timing is ideally arbitrated by
the 110 cpu, I decided to try to trigger the CPU board. There are bare traces
on the board, which function as switches when the conductive rubber
membranes close on them. These go through some diodes to the CPU. I tried
sending 5v pulses on those, but no dice. Lastly, I had tried using a 4016 quad
CMOS switch to use a trigger to close the connections between the switches.
Didn't quite work, apart from some random bursts.

Next to try, when I have some time
I have been reading that CMOS switches and what they are intended to
switch are supposed to be running from the same voltage. Ah. My trigger
circuit and the CMOS switch were on +15v, but the DR110 runs on 6v.

I need to figure out whether or not the DR110 can run off of the +5v provided
by the 707 voltage regulator. Otherwise, on the trigger extracting board, I
might need to make a little 6v regulator.

Since CMOS switches are sensitive, it seems I should probably ground
unused pins on the ic, and run wires which are short as possible, perhaps
even shielded. People typically use 4066 switches more often for this sort of
thing.

If I can reliably get the switches to close in time with provided triggers, then I
can play the DR110 with just about any source! Since there are mods I intend
to do to the DR110 voices, I might just do an all-analog-outs version of the
707, so I have panel room for the additional controls. Then I can get another
707 down the line for grungy digital mods.

Remember, "TR" supposedly represents "Transistor Rhythm" ! >;]P
CJ