Adventures in Synthesis: Modular synth, organ, Rhodes, and drum machine

Published on Mar 4, 2016 Chris Beckstrom

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An early morning experiment combining my DIY modular synth, a Hammond M-100 series organ, a Fender Rhodes, and my DIY iPad drum machine, improvised live and recorded into Bitwig Studio on Linux.

Patch notes:
In the modular, a square wave oscillator is clocking a 10-step sequencer, which is in turn modulating the pitch of 2 saw wave oscillators. The 3rd saw is being modulated by another square lfo (has the effect of a slow sort of trill between two notes). All 3 saws go into a low pass gate which is modulated (pinged) by the master clock, then into a distortion module, then a modular mixer, the big mixer, and finally into the computer.

The organ has a spring reverb unit that takes an RCA input from the tone generation section of the organ. As it turns out, if you unplug the RCA plug from the reverb you have a direct line out of the organ. The organ goes into the modular via preamp, then directly into the computer via an audio interface. I stuck a little screwdriver in the second manual on the organ and rested a trombone case on the Bb pedal so the it would sustain those notes.

The Rhodes is going into a tube preamp which is connected (alligator-clipped because I didn’t have the right adapters) to the built-in input on my Mac.

The iPad is running MobMuPlat, a platform for running Pure Data patches on iOS with a custom GUI. The drum machine is my own creation and it’s working out great! I have a little audio interface plugged into the camera adapter kit, and the output of the modular’s master clock is going into the interface. I added an external input “circuit” in the Pure Data patch, which lets the sequencer listen for incoming sounds and use those as the clock. (This is why a few times you can hear the sequencer skip some beats– when I jostle the alligator clips it misfires!). The iPad goes into a preamp in the modular, then to the big mixer, then into the computer.

Each of these sounds has their own track in Bitwig, which is a first for me– usually I record everything mixed down to mono or sometimes stereo. Some of the reverb comes from the spring reverb in the big mixer, some of it is a reverb plugin in Bitwig.

The organ is an additive synth, and moving the drawbars I can control the balance of various sine-like “oscillators” (tone wheels). Some day I’ll figure out how to use CV to control the drawbars, but for now I’ll just use my hands."