drumBs analogue percussion PCB's

The circuitbenders.co.uk drumBs module is a tweaked version of the Syntom II, an analogue percussion project first published nearly four decades ago in the April 1983 edition of the mighty Electronics & Music Maker Magazine.


drumBs PCB

The drumBs PCB can create a wide range of basic analogue percussive sounds. Essentially these are the kind of sounds that relate to modern drum machines like an Analog Rytm, Alpha Base or Tempest in the same way as a Commodore 64 relates to the latest Apple Mac. On paper its shit in comparison, but it's cheap and fun, and theres a certain dirty basic DIY magic to it that you don't get in more complex machines.
The drumBs synth section features both a VCO and a noise source, along with a resonant noise filter and an auto roll function.To drive the board you will need a source of standard +5v trigger pulses or gates. It can be built in both a Eurorack or standalone format.

drumBs x3

The drumBs controls are:

DECAY: The decay of the percussion envelope.
BEND: The depth of percussion envelope applied to the pitch of the VCO and the filter cutoff of the noise source.
PITCH: The basic pitch of the VCO.
CUTOFF: The cutoff frequency for the noise filter.
REZ:  The resonance of the noise filter.
PULSE: The level of an initial clicking attack at the start of the percussion sound .
MIX: The mix between the oscillator and the noise source.
ROLL: The repeat rate of the auto roll function.
TRIGGER INPUT: The trigger input accepts a standard +5v trigger pulse or gate to trigger the module.
ROLL GATE INPUT:  The roll gate input activates the auto roll function whenever it receives a gate or longer trigger voltage. When the auto roll function is activated the module will automatically retrigger itself at a rate set by the roll knob for as long as the voltage is present at the input. This can be very useful for creating unusually timed fills and rolls, although at its highest trigger rate the roll function can sound like a constant VCO tone.

The standalone build also features an optional and arguably pointless trigger sensitivity control and an output volume pot.

You can find the build guide for the eurorack version HERE and the standalone version is HERE.

Click on the image below to download the schematic.

Below you can see a couple of demo videos using three of these PCB's built as eurorack modules.


There are three parts available. The main board contains all the synth circuitry and can be built as a standalone unit with the addition of a selection of pots and a couple of extra parts. The pots board is designed to be screwed onto the front of the main board and mounts all the pots for a modular synth build along with some extra circuitry to allow the auto roll to be triggered by modular synth gates. Finally a eurorack sized front panel bolts onto the pots board so you can mount the whole thing in your modular synth.

To enable people to build this thing however they want, we are selling the main board and the pots board separately, as well as a bundle option that includes the main board, the pots board and a eurorack front panel of your choice.

If you want to build the standalone version just buy the main board. If your want to build the eurorack version but have your own panel design buy the main board and the pots board. If you want to build a eurorack module with one of our panels then buy the PCB bundle.

drumBs main PCB: £7

drumBs main PCB

drumBs pots PCB: £6

drumBs pots PCB

drumBs eurorack PCB bundle: £16

This includes the two PCB's above plus a front panel of your choice from the selection shown below. Leave a note at the checkout to say which colour panel you want. If no note is left we'll send a black one by default.

The module is 8HP wide and draws approximately 30ma on the +12v rail and 20ma on the -12v rail

Before anyone asks, no the badly dehydrated piss yellow ones aren't available due to the logo of the PCB material manufacturer sometimes appearing randomly on the panel through the yellow soldermask.

If you've done something interesting with one of these boards then send us a photo and we'd be happy to feature it on this page with a link to whatever you do.