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AceTone Rhythm Ace with MIDI

March 25, 2012

The drum machine/rhythm box is a classic, the first from AceTone, which became Roland.  But it was a preset thing intended as simple accompaniment for the organist, no trigger inputs or buttons to individually trigger sounds.

I get quite a few emails about this one.  I’m always a bit sheepish to reply to those who inquire about this particular mod, since it was a quick one done over a weekend with a board from HighlyLiquid that I had ended up not using for another project.

The problem is that the Rhythm Ace is very much an analog machine and some of the drum circuits are quite sensitive to the peak voltage of the trigger pulse, which in some voices needs to be up to 7 volts to get full volume.  I learned this during my blind exploration of the circuit board with an oscilloscope.  I’ve never seen schematics for this machine, so very much trial and error here.

The way I implemented the trigger for all the voices was the same:  from the HL board, deliver a pulse to a transistor to provide an exponentially decaying pulse (what I assumed the RhythmAce voice was expecting).  The peak of that voltage could only be up to 5V max (PIC microprocessors aren’t very tolerant of voltage supplies wider than that), so some of the voices are a bit quiet when triggered through MIDI.

I’m sure a better MIDI-trigger circuit can be built than this, but for all those who’d like to know how I did this, here it is.

I posted the video of it on Youtube

As always, if you do the mods and post them online anywhere, I like to receive credit! 🙂

Good luck!

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