Chris Beckstrom

Fiercely Eclectic Michigan Producer • Activist • Maker • Generalist

The Modular

I built a modular synthesizer from scratch!


For a long time I'd pined for a fancy modular synthesizer, but looking at the steep prices I knew I'd never be able to afford a system large enough to satisfy my aural explorations. In the Spring of 2015 I bought a soldering iron, ordered some components, and started playing with electronics. I wanted to see if I could build a synthesizer, one piece at a time, without any electronics background, math skills, or experience.

I could! One of the many revelations I've had throughout this process is that with a little enthusiasm, some persistance, and a lot of free time, anybody can build synthesizers. They may not be perfect, pristine, or commercial-grade, but they make noise.

...And you can too!

I want to encourage more folks to try building sound-making devices. I want to remove barriers preventing those who are interested in modular synthesis from experimenting with it.

I think we need more diversity in the electronic music community, especially when it comes to modular synthesis. We need more people who aren't upper middle-class white dudes wiggling knobs, and perhaps one way to accomplish that is to get folks building their own inexpensive music-makers.

A synthesizer doesn't have to be expensive, and you don't need to be an electrical engineer to build one. I post many of my circuits on GitHub.

I'm considering writing some tutorials or perhaps even a book about my process; the lofi, lowest-cost-possibleynthesizer building method. More info coming soon!

Here's what it looks like

Some folks have asked for some close-up shots with nothing plugged in, so here you go! I know it can be tough to see what's happening in YouTube videos. I'm constantly moving modules around, building new ones, and fixing broken ones, which means the modular is always changing. Here's what it looks like as of January 2017:

Here it is in action

My synth "format" and construction

Originally I intended to follow the Eurorack format (which I think is ±12V with +5V for digital modules) but I’m not skilled enough (nor did I have the right wall warts) for that. Instead, my synth uses ±9V (from a +20V wall wart) and +5V (from a +6V wall wart). The size is mostly Eurorack (3U tall) and I’ve built my cases standard rack size widths (19″).

My panels are constructed out of 1/8″ plywood, mostly oak, and decorated with sharpie markers. For connectors I use #6 nuts and bolts and connect them with alligator clip patch cables I make using clips and boat trailer wire I get at the grocery store (comes in cool colors). I got this idea from this amazing creation by PHOBoS on the electro-music.com forums.

My general focus has been on building basic modules that can be patched to make cool sounds. I also use a lot of LEDs because blinkenlights are awesome.

I currently (January 2017) have about 50 modules that include around 15 oscillators (mostly square waves) and lots of ways to manipulate them (filters, logic modules, shift register, sequencer, comparator, dividers, envelopes, LFOs, amps, etc). I also have a sort of “skiff” that includes a very primitive keyboard and a breadboard mounted into a panel for easy circuit building. My synth is built into 4 19″ x 6U cases (24U of modules) constructed out of wood from reclaimed pallets.

In addition to the DIY modules, there is also a broken-down Korg Monotron Duo I use primarily for the excellent low pass filter.

About the circuits

I know very little about how these circuits actually work– 99% of the circuits come from the internet, especially the following places:
electro-music.com DIY forum
electro-music.com Lunetta forum
– Nicholas Collins’ “Handmade Electronic Music” (2006)
– Fun with Seamoss website (no longer up)
Hackaday Logic Noise series
Ken Stone’s Modular Synth site
Yu Synth DIY

Thanks to all those folks for sharing their designs! Please don’t look at my circuits, go see the originals. Those folks know what they are doing. My circuits are only here for reference, just to show you can build a great-sounding synthesizer with extremely primitive circuits.

Building the circuits

If you're feeling adventurous, don’t just build these circuits– breadboard them first! I made many small modifications that may not be reflected in the schematics; also, I barely understand anything about electricity so take everything with a grain of salt. If you know your way around electrical engineering you will probably see about a million things I’ve done incorrectly. That said, my synthesizer works and sounds awesome, and I haven’t blown anything up (except for a handful of ICs, resistors, LEDs, pots, transistors, and other components).

More info

Circuits, code, panel design, PureData patches, Arduino sketches, etc: https://github.com/chrisbeckstrom/diy_modular_synthesizer/
Hackaday IO project: https://hackaday.io/project/5826-diy-mostly-analog-modular-synthesizer

LIST OF MODULES

updated January, 2017

OSCILLATORS/GENERATORS

AUDIO RATE

VCO (saw, square, triangle, short pulse)
VCO (saw, pulse)
Triple saw VCO
Arduino wavetable synth voice with MIDI DIN input
VCO (square, half saw)

LFOs

square LFO ("pulse")
LFO (not exactly working)
LFO x3 (square, "triple clock")
LFO x5 (square LFOs)
"Clockfest" square wave/clock x5
LFO (triangle, very slow to audio rates)

OTHER

CMOS noise
White noise (HP, LP, regular)

VCAs

VCA (op amp + transistor, diode)
VCA (transistor)
low pass gate VCA/filter
dual VCA (vactrols)
VCA (vactrol)

SEQUENCING

10 step sequencer (CV and gate)
10 step sequencer (microcontroller-controlled/Arduino, CV, gate, CV step address)
4-stage shift register
4-stage sequential switch

ENVELOPES

envelope generator (A/D)
slope generator (rise/fall)

CONTROLLERS

shotgun shell photoresistor (i.e. light theremin)
expression pedal input
arbitrary voltage controller (keyboard-type thing with gate and CV outputs)
ribbon controller

OTHER

sample and hold
"space noise" (psuedo-random signal source)
gate to trigger converter (x3)
gate to trigger converter, passive (x4)

HARMONICS/WAVESHAPING

voltage controlled low pass resonant filter
voltage controlled low pass + high pass filters (can combine for band pass)
twin T drum/bandpass filter
voltage controlled diode clipper (positive and negative)
dual comparator
square wave to stepped saw wave converter/generator

EXTERNAL INPUT/DISTORTION

Preamp (LM741)
preamp x4 (set gain x5)
preamp/distortion (with lots of gain)
stereo preamp (for iphone, etc)
iPhone holder + power with audio outputs [broken]
Envelope follower

LOGIC

quad NAND gate
quad AND gate
quad XOR gate
logic inverter x3
logic inverter x2 (part of stepped saw module)
r/2r ladder (digital to analog converter)

MIXING

4 input inverting mixer
4 input inverting mixer
3 input non-inverting mixer
3 input 3 output passive matrix mixer
diode mixer / ring modulator
passive attenuator x3
passive attenuator / i/o (headphones)
single attenuator
sequential switch

EFFECTS

delay (pt2399)
spring reverb (it's in its own case)

UTILITY

dual control voltage processor
simple slew (capacitors)
gate to trigger converter (x1 active, x2 passive)
clock divider (powers of 2)
clock divider (/2 /3 /4 /5 /6 /7 /8 /9 /10 /16)
dual comparator
physical switch (bolts)
breadboard
"Mission control" module: an arduino with every pin brought to the panel. Currently it's being used as a serial MIDI to control voltage/gate/trigger converter. (In other words, I can play MIDI on my computer and make the modular do stuff)

MISC

trunk line (4 busses via cat5) x2
jack converter (banana, 3.5mm, bolt, 1/4")
jack converter (bolt, 3.5mm, 1/4")
misc (button, switch, power connections)
oscilloscope connections
power supply (+-9V)
monotron duo
external controller power (for skiff)
power (+5V)
3.5mm jack to bolt converter