MATRIXSYNTH: CB55 analog drum machine, 16HP eurorack build

Tuesday, April 13, 2021

CB55 analog drum machine, 16HP eurorack build

video by Jon Petter Skagmo

CB55 is a DR55 clone pcb from You can find addtional posts featuring the CB55 here.

This one was built by

"CB55 analog drum machine (16 HP)

This one is popular to mount in Eurorack. I started off trying to make a 28 HP module, but i didn't see the needs for all the modifications/pots I planned, and I thought the module was too large, so I started over and made a narrow (16 HP) MIDI enabled module.
Based on the Circuitbenders CB55 analog drum machine PCB
Cut off the entire trigger conditioning circuit and drilled new mounting holes to allow the PCB to be placed vertically behind a Eurorack panel.
Designed a MIDI and sequencer addon with a PIC18, with a switch on the front panel to start/select predefined sequences, and a DIN-5 for MIDI in. This PCB also has the voltage regulators and power connector, as that was chopped off together with the trigger conditioning circuit.
In addition to the standard volume, tone and accent pots, there are individual volume pots and jack outputs for each of the voices.
Panel was milled from the rear side because I needed to machine some pockets for some protuding tabs on the potmeters, and then flipped over to do the engraving."

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