Build your own synthesizer
The whole do-it-yourself (DIY), open source maker electronics scene that’s really gained in popularity over the past few years has led to a lot of really interesting devices and kits appearing on the market. The great thing, of course, is that it isn’t just limited to computing and robotics enthusiasts: musicians have benefitted from this open source DIY movement too.
We’ve started seeing a lot of synths with open access to both the hardware schematics and the software or firmware (if any) at the heart of the synth.
DIY synths aren’t a new thing, but until a few years ago they used to be either super simple square wave toy synths or complex analog synths, with very little in between. These days, there’s a lot more to choose from, especially with the advent of microcontrollers running easily hackable firmware.
Here are 5 great open source and DIY friendly synths that you can play, build, modify or even use as jumping-off blocks for your own synth creations, listed in rough chronological order.
Recommended Reading: 10 Virtual Instruments You Can Play In Your Web Browser
1. Mutable Instruments – Shruthi
Mutable Instruments’ Shruthi is a hybrid digital and analog monophonic synth that uses an 8-bit microcontroller to generate two oscillators plus a sub frequency oscillator. The Shruthi-1’s oscillators are quite capable, though, and aren’t just limited to the square waves that you normally expect from DIY synth kits. Since they’re digital, the oscillators are also capable of wavetable synthesis and a smorgasboard of weird and “out-there” digital tones, such as formant synthesis and bit-crushed videogame-esque sounds.
The filter is all-analog, and by default the Shruthi comes with a four-pole low-pass filter. However, the fact that the filter is on a separate PCB means that you can easily swap filters, and there are a lot of different flavors of filter available for you to buy or build. The Shruthi-1 also has an audio input, so you can use the filter to process external audio. The Shruthi-1 only comes in kit form and will require assembly. [3 kit; .50 – 5 enclosures]
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2. Lush Projects LushOne
The LushOne is a system of small, low-priced synth modules, covering everything from base oscillator and filter combination, to sound-shaping envelopes to some effects and additional control. All of these modules are connected to each other using small patch leads, letting you route signals and create sounds totally from scratch. The base unit contains two digital oscillators with five waveforms coupled to an analog filter, like most other synths in this list.
The Contour kit adds an ADSR envelope, a voltage-controlled amplifier (VCA) and a ring modulator. There’s also an Echo kit for adding echo effects to the LushOne. The LushOne can be controlled via MIDI, but it also can interface with other modular equipment, since it has control voltage (CV) inputs for elements such as oscillator pitch and filter cutoff. The LushOne base unit and the additional modules all come as kits, and requires intermediate soldering skills. [7 – 9 modules; .50 – 9 cases]
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3. PreenFM 2
The PreenFM 2 is an open source, polyphonic, frequency modulation (FM) synth, with quite a lot of features packed into a small case. The PreenFM 2 actually consists of four separate and independent synth instruments in one little case.
Each of these instruments is quite well-equipped, with seven different modulation sources, a powerful arpeggiator sourced from Mutable Instruments’ algorithms, an effect slot for filters as well as one gate effect. Each instrument can be set to respond to different MIDI channels so they can be played independently, or set to respond to the same channel for really rich tones.
The PreenFM 2 has between 8 and 16 voices of polyphony, great for big chords. It responds to MIDI via USB, so you can plug it directly into your computer and control, sequence and play it directly from your digital audio workstation (DAW) of choice, without needing any MIDI ports or MIDI to USB converters. It also supports a USB stick for storing presets. It even supports presets from Yamaha’s classic DX7 synth. The PreenFM 2 comes as a kit, case included, and will need assembly. 
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4. LittleBits Synth Kit
No list of open source synths would be complete without one of the highest-profile open source synth kits available today, the LittleBits Synth Kit. Designed in conjunction with Korg, the LittleBits Synth Kit is a collection of small synth modules that are completely modular – like the LushOne – and just snap together like Lego blocks, letting you create some reasonably full-featured synths from some basic building blocks.
Modules include a dual oscillator module, a filter module, a keyboard, an envelope and a micro sequencer, amongst others.
And, since the Synth Kit is built on the same platform as all of the other LittleBits kits and modules, it’s very easy to integrate a synth into other, more complex electronics creations. The LittleBits Synth Kit is a bit lacking in connectivity at the moment, but connectivity modules – MIDI, CV and a USB input/output module – are coming over the course of the year, letting you integrate it into your existing workflow a lot easier.
The circuits are all open source, although the connectors themselves aren’t. [$159]
5. Meeblip Anode
The Meeblip anode is the latest synth in Create Digital Music’s line of Meeblip synthesizers, one of the biggest names in the world of open source hardware synths. The Anode is a hybrid digital and analog monophonic synth that combines square wave digital oscillators with a rich analog filter that covers a lot of sonic ground.
The Anode has a particular emphasis on generating bass sounds, and if you give a listen to the demos, you’ll find that the combination of 8-bit digital oscillators and an analog synth really help it create some rich and in-your-face bass sounds.
The Meeblip Anode might seem toy-like, but it’s a very capable synth: beyond the oscillators and resonant analog filter, you have some basic envelope controls, pulsewidth control for the oscillators as well as a low frequency oscillator (LFO) that can modulate either the filter cutoff or pitch of the oscillators.