[sdiy] Negative-going triggers in the Boss DR-110 drum machine - Why?

Benjamin Tremblay btremblay at me.com
Fri Sep 29 14:45:11 CEST 2023

Sorry, just to be clear here I will describe what I have seen, not what I think I know, which is probably flaky.

In 1993, I bought a DR-110 from a local shop for some very small sum.
I soldered the triggers into a TR-909, stuffed the DR-110 PCBs in a plastic bag, and duct-taped it into the 909, and drilled random holes into the 909 for 1/4” phone jacks. It sounded great. 
This year, I got a DR-110 for cheap on eBay. It powered on and sounded fine.
Being older and wiser, I carefully took apart the DR-110, desoldered the ribbon connector between analog and digital boards, put the analog board onto my bench and powered it up with 6V.
I probed the wires, looking at the same service manual schematics as shown here.
I found: All the trigger inputs except the kick drum have pull-up resistors and respond when grounded.
Because of the pull-ups, it was easy to use 2N3904 transistors to trigger them with a positive signal. 
The kick drum only responds to a positive pulse.
It has a pretty big resistor at the input. I did not bother to make the resistor smaller for a clickier kick.
The clap needs a clever sequence of pulses. I did not attempt to generate those pulses. Just pulsing the clap one time provides excellent backdrop for the Drumbrute clap.

Benjamin Tremblay
btremblay at me.com
330 Fiske Street
Carlisle, MA 01741

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