Open source eurorack modules

These are some open source eurorack modules I have found from across the internet, with PCBs or schematics available. My dream is to build my own modular synth entirely out of open designs. This has many benefits:

Great way to learn electronics
Cheaper (according to some guy on reddit who saved 50% doing everything diy)
Open designs can be improved upon (Notice all the Mutable instruments derivatives, for instance. Many are just clones, but a lot of work has been done by the community in the software space)
Open source helps to destroy capitalism somehow

This list doesn't have everything, in fact I think I'm just scratching the surface, but it's pretty long at this point so my initial research phase is over and my next step is to pick out a few to make a 42-84HP synth. I'll probably add more youtube videos to this list demonstrating some of the modules, though.

So far my favorite modules that I am considering:

EuroPi to add programmability
Time Machine because it's cool
Befaco Noise Plethora because it's cool
A Matrix Mixer to do weird feedback stuff
Mutable instruments Rings, Clouds, and Plaits
Synth Fox advanced clock source and Punk SVF

Module	HP	Description	Power Usage
Multimult	8HP	6 way buffered multiple
Sloth	4HP	Slew Limiter
Pique	4HP	Mutable Instruments Peaks
Baker	6HP	Mutable Instruments Peaks
Rainier	8HP	Mutable Instruments Peaks
Beehive	8HP	Mutable Instruments Plaits
nRings	8HP	Mutable Instruments Rings
Monsoon	12HP	Mutable Instruments Clouds Variation
Time Machine	22HP	Delay	122mA
Uncertainty	2HP	Randomly Drops Triggers
Noise Plethora	14HP	Noise Monster	110mA
Out V3	4HP	Output Module	24mA
EuroPi	8HP	Programmable Module
Matrix mixer	18HP		20mA
Mak Mak	12HP	Quad VCA, Attenuator or 3 channel mixer
Cha Cha	6HP	Square core low frequency oscillator with four waveform outputs	20mA
Kra Pao	12HP	A resonant low pass gate at is core, though it can function in three different modes, as a VCA, a LPG or a VCF (Low Pass)	15mA
3xVCA	6HP	Linear VCA Trio	30mA
Helium	6HP	three channel, 1-to-3 buffered multiple and a 3-to-1 precision adder	35mA
Enhanced Clock Source	?		?
uO_c	8HP	programmable module	?

Here's one idea for a 84 HP setup:

Module	HP	Description	Power Usage
uO_c	8HP	programmable module	?
uO_c	8HP	programmable module	?
nRings	8HP	Mutable Instruments Rings
benjolin gorga	16HP	Chaos oscilator	?
Time Machine	22HP	Delay	122mA
Matrix mixer	18HP		20mA
Out V3	4HP	Output Module	24mA

I'm curious about converting the 4x4 matrix mixer to 3x4 for some HP savings...

Or 42 HP:

Module	HP	Description	Power Usage
uO_c	8HP	programmable module	?
benjolin gorga	16HP	Chaos oscilator	?
uO_c	8HP	programmable module	?
3xVCA	6HP	Linear VCA Trio	30mA
Out V3	4HP	Output Module	24mA

Please be aware of the license for each module and act ethically. Most of these are made available by small companies or individuals, so consider buying the kits or pre assembled modules to support their efforts if you're able to.

Befaco

Noise Plethora - 14HP

This one is one of my favorites. It sounds amazing!

Voltio - 6HP accurate voltage source and precision adder

I'm not exactly sure how this would come in handy but it looks interesting

Slew Limiter - 6HP

Out V3 - 4HP output module

Bandit - 8HP

Bandit is a fun combination of band-pass filters, VCAs, and routing options. It serves multiple functions including equalizer, crossover, multiband VCA, 4 band spectral mixer, and spectral external FX insert point.

VC ADSR - 8HP

Swirls

Swirls is a 8HP version of Mutable Instruments Tides

Github Source

Tides is all about waves that go up and down, from minute-long cycles to audio rates… This module is Mutable Instruments’ unique take on the looping AD envelope generator – pushing this well-known trope to unknown territories.

The core of the module is a digital asymmetric triangle function generator, which can be used in AD and AR modes (for envelope generation), or looping (as a VC-LFO or VC-DO). The triangle generator is followed by a wavetable waveshaper providing linear, exponential, logarithmic, sinusoidal, or arc-sinusoidal shapes for the A and D segments. Then, a second processor applies either a 2-pole low-pass filter to the waveform, smoothing its sharp edges; or a rubbery wavefolder, adding kinks and “bounces” to the waveform. Because Tides has been designed from the ground up to work at audio rates with minimal aliasing, and because all its parameters are under voltage control, it can be used as a unique self-contained synth voice.

The Leech

Passive distortion

I can't seem to find PCB files for this one, but the schematics are available!

This looks like a really fun module that can be built with basic parts. I also like that it's a passive module; You can plug in audio from your phone or mp3 player, plug in some headphones, and you've got the worlds smallest eurorack system!

Erica Synths DIY Modules

Module	Description
Bassline	all in one synth voice for acid basslines and drones.
BBD delay/flanger	all analogue effects unit based on V3205 BBD IC.
Delay	tape and digital delay unit with tap tempo, tempo sync, reverse, hold and add functions.
Dual VCA	Polivoks architecture inspired dual VCA, rare Russian differential opamps are now replaced with AS3360.
Envelope	recreation of Polivoks envelope generator with loop and end of attack functions.
MIDI-CV	Polivoks functionality inspired dual MIDI-CV converter with glide function.
Mixer	simple 3 chanel audio mixer.
Modulator	Polivoks functionality inspired LFO, noise and S&H module.
Output	Output module with headphone amplifier.
Polivoks VCF	authentic recreation of the Polivoks VCF.
Swamp	our take of Wogglebug module with lots of unique extras.
VCO3	Polivoks inspired VCO with nice extra – VCO Sync input.

tpcarlson synth-diy

eurorack designs and kits by tpcarlson

Github source

Module	Description
Dice	16hp, clickless signal router
DrumFiend	8hp, 19 channel triggers-to-MIDI converter
Kinky Lynx	8hp CV swiss army knife, a clone of the Mutable Instruments Kinks and Links modules behind a single panel
LPG	4hp Low Pass Gate with a vacrtrol at its core, based on the LPG & CV Tools module
Mix	3hp, 4-to-1 mixer based on the CGS04 DC Mixer
Multimult	8hp, 6-way Buffered Multiple
Pentanoise	4hp, 5-way binary white noise source using the ElectricDruid Pentanoise chip
Pirate Radio	4hp panel for Radio Music
Sloth	4hp Dual Slew Limiter with state LEDs, based on the dintree D107
Through	4hp dual-use 1:1 connector block, or passive multiple
Turing Machine Panels	Panels for the Turing Machine, and Volts and Pulses expanders
VCA	6hp Dual VCA, based on the ElectricDruid LM13700 VCA
VCADSR	16hp, Voltage controlled ADSR, ased on the ElectricDruid EnvGen8 chip
VCDO	10hp, Wavetable VCDO using the ElectricDruid Wavetable chip
YARM+	4hp Ring Modulator, based on the René Schmitz YARM+ design
YASH	5hp Sample and Hold based on the René Schmitz YASH design, with some modifications

Plinky

8-voice polyphonic touch synthesiser

I see most people using plinky as a standalone synth, but I would be more interested in using it in a case with other modules and MIDI input.

I ran into some issues sourcing a few parts from the BOM, but DIY kits are still available.

diysynth

Gerber files and schematics of various modules

Module	Description
3320 VCF	6HP, Voltage controlled lowpass filter
3340 VCO	4HP, Simple v/oct VCO based on the legendary CEM3340 (AS3340) ic
ADSR envelope generator	4HP
buffered multiple	3HP, 1 in and 3 out buffered multiple module
cycling envelope generator	4HP, Can be used as an envelope generator or as a 'LFO'
DIGILFO	6HP, VCLFO Can produce eight different waveforms (ramp up, ramp down, square, triangle, sine, sweep, random steps, random slopes)
dual VCA	3HP, uses a LM13700 OTA
looping attack/release envelope generator	6HP
noise lab	3HP, Noise module that is able to generate analog and 'digital' noise
passive low pass gate	2HP
power supply unit/module	6HP Standard AC to bipolar 12V Eurorack PSU
sub modulator	6HP, advanced sub-oscillator that generates square waves with various forms and frequencies

Free Modular

open source software and hardware schematics for Eurorack modules

This repository contains open source software and hardware schematics for Eurorack modules which are designed to be assembled easily and cheaply without any technical knowledge. Every module should be able to be assembled for around $20 in about an hour of work, even with limited experience.

Module	Description
Clock	A basic, 8-channel clock source with adjustable tempo, phase shift, pulse width, and swing.
Envelope	A simple but powerful envelope generator that can cycle between 4 separate modes: traditional ADSR, AR with tunable curves, and two looping modes.
RNG	A module for creating semi-looping, randomized CV and gates. Inspired by the Turing Machine
Offset/Atten	A utility module to scale, shift, and invert signals.
Mixer	A 5-input active mixer for audio or CV. Can be daisy-chained together for larger mixes.
Output	A stereo line out and headphone amp with VU meter
Drift	A modulation source for creating organic, always changing, never repeating control voltages. The main algorithm is based on Perlin noise, but there are three other algorithms to choose from if you want a different flavor.
Boost	A distorting, overdriving analog amplifier. Can be used to boost line-level or microphone signals with gentle overdrive, or to heavily distort Eurorack audio.

OAM Time Machine

Delay capable of rhythmic glitch effects, reverbs, and chaos

This is the most versatile delay I've seen so far, capable of much more than just "delay". The microcontroller also has quite a few unused CV inputs and outputs which you can access through an expansion module.

(also, I know everyone loves the huge sliders, but if we shrank them just a little, maybe we could fit the extra jacks at the bottom? pls don't kill me)

Even though the module isn't tiny, the versatility makes me think this would be an amazing choice for a smaller setup.

As far as I'm aware, there's no PCB available for this one, but the schematic is available on the github. Seems simple enough to hand wire.

After Later Audio

Open source modules from ALA I am interested in:

Module	Description
Alan	6HP version of the Music Thing Modular Turing Machine
Alan 1U	1U version of Turing Machine
Baker	6HP version of Mutable instruments Peaks
Rainier	8HP version of Mutable Instruments Peaks
Bog	8HP wogglebug module based on Erica Synths Swamp
Flip	1U version of Mutable Instruments Branches
Monocle	4HP, Half of a Mutable Instruments Blinds
Popple	8HP stereo filter based on the Mutable instruments Ripples V1 filter section
SHTH	Sample & Hold / Track & Hold
Threads	1U MIDI interface Module based on Mutable instruments Yarns
uO_C 1U	1U variant of Micro Ornament & Crime by mxmxmx

misc

other interesting resources

Here are some other resources for further reading, including some modular designs I haven't read up on yet.

Discussion on a Matrix Mixer design
Mod Wiggler DIY forum
Supersynthesis
Matrix mixer
Synthesizer DIY resources
Benjolin - Rob Hordijk's Benjolin in the Eurorack format
Blattwerk Eurorack modules designed by Lorenz Neumann
Printable Instruments
HAGIWO - Lots of DIY modules
3xOsc - 3 VCO Eurorack Module
Multi Saturation Module - PCB and Schematics for a eurorack module, not sure if it's completed or still WIP. Lots of other designs on their github
Fihdi Eurorack Github - Lots of Modules here
Mystrix - Open source grid controller
René Schmitz DIY synth page - Lots of schematics
Synth DIY Wiki
Experimentalists Anonymous DIY Archives
electro-music DIY forum
- Schematics Vault
- Schematics listing by type
- Quick reference links - lots of these links look dead, but maybe archived somewhere? :(
- PCB/ Schematic Quick Reference
bastl instruments github
bastl instruments website
Turing machine
lookmumnocomputer - Looks like a lot of the modules have the schematics published. Also check out his youtube and music :)
MothSynth - credit card sized affordable Sampler / Synthesizer
Skull & Circuits - Some of these have schematics available, worth looking more into
odeliy schema cave - Various old schematics of retired and unreleased modules.
Robot Dialogs - Lots of open module designs with pcbs
Craig Lee
modularsynthesis.com modules
Cursed Audio modules
Dirtbox Layouts
sdiy
avalance vco
Cagey Music and Synth DIY - blog with lots of original designs and also builds of other open designs to check out
Feedback Modules shop - looks like they provide schematics for some modules
Schräg multimode filter github
Reed Ghazala
Experimentalists Anonymous
macumbista.net
yusynth DIY 5u modules
Fonitronik synth DIY
eurorack awesome
sdiy list of synth DIY repositories

Benjie Jiao modules

PCB Available

Module	Description
EurorackBusBoardJST	A power distribution board for Eurorack power levels but with JST2.54 connectors.
MiniADSR	A four-parameter envelope generator.
MiniBurst	A CD4017-based burst generator
MiniDelay	A three-knob PT2399 delay module.
MiniLFO	A 2HP triangle wave LFO
MiniMix	A 4-channel mixer.
MiniMult	A passive 2HP mult.
MiniOSC	A volt-per octave, dual waveform VCO.
MiniSNH	An analog sample-and-hold module with probability gate controller.
MiniVCA	An two-channel LM13700 VCA.
MiniVCF	A diode-ladder voltage controlled low pass filter.
MiniVerb	A reverb module based around the Daisy Seed platform.

Schematic Available

Module	Description
BufferedMixer	A buffered 12-channel mixer
GranulArduino	An Arduino-based granular synth using grains based on two triangle waves.
Kwantizer	An Arduino-based CV quantizer
Oras	An Arduino-based programmable clock module
OrasPatternGenerator	A pattern generator for my Oras Programmable Clock module.
RandomTriggers	An Arduino-based sample and hold program that takes in white noise and uses it to produce random signals.
ThreeChannelTriggers	An 8-Step Sequencer with 3 independent trigger output channels.

Mutable Instruments

Eurorack Modules by Emilie Gillet

AMAZING modules by Emilie Gillet. These are some of the most influential modules in the modular scene, it's incredible they are open source now. Many thanks to Emilie.

Github source

Module	Description
Blades	Dual multimode filter.
Blinds	Quad VC-polarizer.
Braids	Macro-oscillator.
Branches	Dual Bernoulli gate.
Clouds	Texture synthesizer.
Ears	Contact microphone.
Edges	Quad chiptune digital oscillator.
Elements	Modal synthesizer.
Frames	Keyframer/mixer.
Grids	Topographic drum sequencer.
Kinks	Utility module - rectifier, analog logic, S&H, noise.
Links	Utility module - buffer, mixer.
Marbles	Random sampler.
Peaks	Dual trigger converter.
Plaits	Macro oscillator.
Rings	Resonator.
Ripples	Liquid 2-pole BP, 2-pole LP and 4-pole LP filter.
Shades	Triple attenuverter.
Shelves	EQ filter.
Stages	Segment generator.
Streams	Dual dynamics gate.
Tides	Tidal modulator.
Veils	Quad VCA.
Volts	+5V power module.
Warps	Meta-modulator.
Yarns	MIDI interface.

winterbloom

Modules I am particularly interested in:

Castor and Pollux - A Juno-inspired dual oscillator
Neptune - Salty diode ladder filter
Helium - A triple 1-to-3 precision buffered multiple and 3-to-1 precision adder
Micronova - Small Eurorack power supply

EuroPi

fully programmable 8hp module using a rasperry pi pico

Matrix Mixer

like a standard mixer, but with more options for introducing feedback

I think matrix mixers are slept on. This is one of the first builds I want to do.

Music Thing Modular

Modules by Tom Whitwell

Website Github

Lots of good reading on this website, as well as schematics for eurorack modules. I'm also pretty excited for the Workshop System :)

Here's just a few modules. They all have schematics available, and a few have gerbers available.

Module	Description
London Drive	London Drive is a simple but pleasing distortion circuit and a good way to learn soldering.
Mini Drive
Twin Drive	Like the mini drive, but stereo
Turing Machine	binary sequencer, based around a 16 bit memory circuit called a shift register
Graphic EQ	A simple, compact and high quality seven band graphic equaliser for Eurorack.

jakplugg modules

Github

Here are a few of jakplugg's most popular eurorack github repos.

Module	Description
uO_c	8HP version of ornament and crime
motivation radio hardware	ESP32 eurorack hardware platform
Monsoon	12HP clouds variation
T_μ	8HP Temps utile 6x clock generator
nRings	8HP Variant of Rings
Typhoon	Clouds Variant
m-Brane	6HP Yarns Variant
μGrids	8HP Grids Variant
beehive	8HP Plaits Variant
μBurst	8HP Clouds Variant
pique	4HP Peaks Variant
Pachinko	12HP Marbles Variant
Twiigs	8HP Branches with sliders
μTidesII	8HP Tides II Variant
Quarks	22HP Elements Variant
PlancksII	8HP Frames Variant

Synth Fox Custom Stuff

DIY modules by Aubery

I love websites like this, definitely check it out. Website

There's lots of great modules here with long and detailed writeups. Here's a few that stick out to me after clicking on a few random ones.

Enhanced Clock Source

After taking all these requests from me to me into account, i came up with a voltage controlled clock core that has an absolutely insane range, from ticking once every few minutes to literally going into sound range.

VC 4 To 1 Selector

VC 4 To 1 Selector is another useful and universal utility module. Based on the Signal Switch by Rene Schmitz, it is a device that selects one of the four input signals and reproduces it on its single output jack. It covers the entire modular signal voltage range and has super low distortion, making it suitable for both CV and audio usage - and, naturally, binary logic signals, too.

Punk SVF

Punk SVF is my first successful design of a fully solid state filter (no vactrols involved). It got its name for not requiring any special parts whatsoever, being relatively easy to build, and sounding raspy, abrasive, and at times even unruly. It's a cool filter with loads of character and sweet spots! Topologically, this is an unorthodox implementation of an otherwise classic state-variable filter.

Dual Crossfader

This very useful vactrol-based module can crossfade between things. Both CV signals and audio rate signals can be crossfaded with it.

musicdevghost

github page with eurorack modules by musicdevghost

These are production ready modules that musicdevghost lists on their github

I haven't looked at these in depth yet, but they seem to be very well polished modules with PCBs and faceplates available.

Module	Description
Su Su - Bipolar Power Supply	Provides 1A, +/-12v
Tom Yum - VCO	Fully analog voltage controlled oscillator with stable v/oct tracking
Kra Pao - Resonant Low Pass Gate	Buttery resonant LPG/VCA/VCF based on the original design from Thomas White, core design used with permission
Cha Cha - VCLFO	6HP Voltage Controlled LFO with 4 wave outputs and reset input
Sigma	Function/Slope Generator with V/OCT tracking
Mak Mak	Quad VCA/Attenuator or 3 Channel mixer
Leo Leo - The Matrix Programmer	Serge inspired Programmer on steroids

Noise Reap

Module	Description
3xVCA	a trio of high quality VCAs
anomaly	VCF combined with a broken wavefolder
foundation	electro-organic instrument loosely mimicking the thump and feel of an acoustic kick drum
paradox	pair of triangle core VCOs that self modulate

Uncertainty

Stochastic gate-processor that randomly drops gates you try to pass through it