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

[Benjamin Tremblay]

Oh yes, and one more thing. The Drumbrute uses 3.3V logic, so using transistors (with ~1K resistors on the base) was a much simpler approach than using level-shifters and logic chips or dedicated op-amp comparators.

> On Sep 29, 2023, at 8:45 AM, Benjamin Tremblay via Synth-diy <synth-diy at synth-diy.org> wrote:
> 
> 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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> 
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