[sdiy] TR-707 Mods and trigger outputs - advice wanted

[Dan Gendreau]

Steve Jones Wrote:
> I am looking for any info / web sites for modifying the TR707 drum
> machine

IMHO, the TR707/TR727 is one of the best drum sequencers available for
analog drum users today. Now granted, the internal sounds suck, but thats
great, because thats what makes it inexpensive. The sequencer is the key
here. It is easier to program than the TR909 (because of the LCD) and it is
relatively easy to modify. It can even sequence external gear like the
Novation Drumstation.


> is it possible to get more 5v triggers out from this
> machine? (it has 1 as standard).

Well, there are two approaches I might recommend. I have not done #2 yet,
but I did a bit of researching when I first got my 707 and it certainly
seems straight-forward.

1) Audio trigger circuits. This is less invasive of your 707 since you can
build as a separate unit or build it right into your drum synth module.
Essentially, its an envelope follower for each audio channel to be
converted. There are many schematics on the net for such curcuits. Also,
some poeople have reported some success using audio to trigger analog drum
modules directly, but some drum sounds are not well suited for this.

2) Actual trigger outputs. This is more work, but believe it or not, even
though the TR707 has crappy sampled waveforms, it also has an analog
envelope generator for each drum major sound. By major, I mean BD1 and BD2
count as one major drum sound. If you look at the TR707 schematics you
should be able to find them labeled Env Gen(Q21, Q22, Q23, Q24, Q25, Q27,
Q28, IC38, IC39) EGs. The only exception is the CC and RC channels which
have their own roms and DACs, but even these could be set up to output
trigger pulses with a little time, the schematic and some head-scratching.


Let me know if you need the scnematics and I will email them to you.

-Dan G.
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