Microrack Modular Synth: Basics

Microrack is a series of modular analogue synthesizer modules in a very small format designed to plug into a standard 830 point breadboard. The system uses control voltages between -5V to 5V with 1V per octave for pitch. The Microrack power is provided by a module using USB-C or 5V-12V on a centre-positive 2.1mm jack - this puts +12V, +5V, 0V and -12V onto the four breadboard rails. There are currently four generator modules, six sound processing modules and 3 utility modules in the range. The system sits somewhere between Eurorack, AE Modular and the sadly discontinued Korg littleBits synth kit. All of the modules have published schematics.

This article shows three basic module configurations using the Synth Starter Kit.

Microrack was launched as a Kickstarter project in 2024 with an estimated delivery date of December 2024. The founders demonstrated prototypes at SuperBooth 2024. The project started delivering products in March 2026.

UPDATE: second article published on Arp Lead, Jacuzzi + The Drone and Bass N drum patches: Microrack Modular Synth: Exploring the Starter Kit Patches, Oscillator Stability and Noise Output Spectrum

1. Microrack Synth Starter Kit: Microrack

The content of the Microrack Synth Starter Kit is listed below. The name printed on the module appears in brackets if it differs to the full name.

1. breadboard - a standard 830 point (full size) breadboard.
2. set of wires - silicone jumper wires, mostly female to female, one crocodile (alligator), four black male to female and two jumper connectors.
3. power module (power) - generates +12, +5, 0V and -12V from USB-C or 5V-12V on 2.1mm centre-positive barrel connector.
4. oscillator (osc) - a very flexible voltage-controlled oscillator with low and audible frequency ranges.
5. noise + smpl hold (noise s&h) - noise generator and sample and hold.
6. envelope - an envelope generator with attack, sustain and release (but not decay).
7. stylus keyboard (stylo) - a tiny one octave stylus-based keyboard.
8. filter - a voltage-controlled filter with resonance, either low or high-pass.
9. delay - a lo-fi delay.
10. counter - an eight step counter with reset.
11. audio output 3.5 - the output module with a tiny speaker or 3.5mm jack output.

Two cards, a "quick start guide" and a "synth patch (bass & drum)", come with the kit.

1. The power module is not hot pluggable, i.e. the system as a whole is not designed for it to be inserted in a powered state into a breadboard with modules. The is mentioned in the Microrack electrical specification. The power module should be inserted first from a set of modules. An alternative, simple, safe approach is to always unpower the breadboard/modules when making changes.
2. A guitar pedal power supply cannot be used as they are centre-negative. The Microrack power module's barrel connector is centre-positive.
3. The modules must be inserted in the correct orientation. The design allows them to be physically plugged in upside down. The orientation can be seen from the writing on the module and a colour-coded chevron at the bottom of the module.
4. The breadboard colour coding for the power rails is not relevant for Microrack.
5. Module pins are colour-coded: blue for inputs, red for outputs.
6. The breadboard power rail layout and pin spacing on modules may force some modules to be adjacent without a gap. Take care modules are fully inserted and not partly riding atop of an adjacent module.
7. The breadboard's power rail connections may not be quite aligned with the breadboard's holes - this was mentioned in the Kickstarter Update #20 . These can be aligned with careful insertion of a pin (black wires in kit have male pins) or set of pins to improve alignment.
8. The stylus (pin or crocodile clip) on the stylo module should only be pressed on the keyboard or the blue input pins. It's important to avoid the metal dots at the bottom next to the lower C and in particular not to short (press both together) with the end of the stylus.

This plays a continuous tone set by the PITCH potentiometer and FINE potentiometer on the oscillator board. This is useful to test everything works. The potentiometer on the output 3.5 module adjust the volume and this is represented by the 3 bar level LED array on the module.

Modules

1. power
2. oscillator (osc) - set to bipolar (triangle wave with line through the middle), FINE, VCO.
3. output 3.5 - set to MONO.

Connectivity

1. sawtooth out on osc to L (left) on output 3.5 (green).

USB measured current: 0.38A.

This plays a tone set by the one octave stylus-based keyboard with the frequency of the lowest note set using the PITCH/FINE potentiometers on the oscillator board. The tone is still continuous without the use of the stylo's GATE output. The stylo module maintains (holds) the last note played.

Modules

1. power
2. oscillator (osc) - set to bipolar (triangle wave with line through the middle), FINE, VCO.
3. output 3.5 - set to MONO.
4. stylo

Connectivity

1. sawtooth out on osc to L (left) on output 3.5 (green).
2. CV on stylo to PITCH on oscillator (green).

USB measured current: 0.46A.

This plays a tone set by the keyboard together with the PITCH/FINE potentiometers on the oscillator board. When the stylus is pressed on a keyboard note the GATE goes high and this triggers the envelope from the stylo module which is used to give a gradual rise in the volume. When it's lifted there's a gradual fall in volume. The application of the envelope would normally be performed with a voltage-controlled amplifier (VCA) but as the kit doesn't include one the filter's CUTOFF (together with appropriate DEPTH setting) is used to achieve a similar result.

A common specification for an envelope is the ADSR model. The D for decay feature isn't present on the envelope module.

Modules

1. power
2. oscillator (osc) - set to bipolar (triangle wave with line through the middle), FINE, VCO.
3. filter - set to LOW (pass).
4. envelope - set to SUSTAIN on.
5. output 3.5 - set to MONO.
6. stylo

Connectivity

1. sawtooth out on osc to IN on filter (green).
2. OUT on filter to L (left) on output 3.5 (green).
3. CV on stylo to PITCH on oscillator (green).
4. GATE on stylo to GATE on envelope (blue).
5. OUT on envelope to CUTOFF on filter (blue).
6. (black) wire with pin or crocodile clip to +5V on stylo for use the stylus.

USB measured current: 0.57A.

The video above shows the three module configurations shown in this article powered by a USB power pack. The 3.5mm audio output is being amplified, the video's audio is from the room.

1. 00:00 Patch 1: osc module only.
2. 00:05 Set volume on output 3.5.
3. 00:16 Patch 2: osc + stylo.
4. 00:46 Patch 3: osc + envelope + filter + stylo.
5. 01:11 Increasing resonance.
6. 01:46 More resonance!
7. 02:16 Outro with shorter envelope rise (attack).

The sawtooth, triangle and square waves are shown above from traces on an oscilloscope with the oscillator module set to about 440Hz. An FFT showing the magnitude of the sine wave components is shown on top of the trace. Some observations follow.

1. The square and sawtooth waves have a peak to peak of approximately 1.85V, the triangle wave is only 0.85V.
2. The triangle wave isn't very sharp and looks like a sine wave.
3. The oscilloscope is struggling to count the frequency of the triangle waves giving a bogus Fcnt value.
4. The square wave can be seen to spend more time high than low, its duty cycle is about 60% due to the SHAPE potentiometer not being left at 50%. This affects the harmonics too.

Some ideas to explore:

1. Get a second breadboard and bridge the power module across the two breadboards. For full size (830 point) breadboards, ones with continuous power rails are best - these are indicated with blue and red lines that run the length of the breadboard and aren't split at the middle.
2. Experiment with the noise s&h, counter and delay modules from the starter kit. The starter kit includes a card with the following patches.
3. Bass N Drum.
4. Arp Lead.
5. Jacuzzi + The Drone.
6. Check if USB power from a desktop/laptop. a traditional noisy power source, puts noise on the 3.5mm audio output.
7. Draw and save your patches using the (unofficial) Microrack patchbook app.

Other articles/videos on the Microrack

1. DIY Electronic Music Blog: Microrack – First Impressions
2. Parks and Rex: Microrack! - Demo and First Thoughts (YouTube) - more modules on display than just the Synth Starter Kit, at 03:53 the single breadboard is replaced by the rack chassis.
3. Cinematic Laboratory: MicroRack - Modular For The Masses? | Starterkits Ep. 14 (YouTube)
4. Nosnibor Senoj (YouTube)
5. an early Microrack patch
6. two oscillators