x0x-heart Eurorack Module

by Open Music Labs

The heart of a TB303 synth recreated in modular format.

$22,044 raised

of $1,500 goal

1,469% Funded! Order Below

Product Choices


x0x-heart Module

x0x-heart Front


x0x-heart Module - 5 Pack

Intended for distributors (or if you're just looking for a symphonic wall of acid): $215 each.


x0x-heart Module - Kit

Build your own module - the kit includes the panel, the pacemaker, the x0x-heart itself, knobs, Euro cable, etc. Some patience + a soldering iron, and you've got yourself a module. All required soldering is through-hole.


x0x-heart Module - Kit - 5 Pack

A distributor pack for the shops catering to the DIY enthusiasts: $185 each.


Recent Updates

As Featured In

AskAudio Logo


"If you're a fan of acid bass, the original TB-303 and Eurorack synth modules, then this one is for you… With the module being sold for the appropriate sum of $303 it’s easy to see why this has been snapped up so quickly."


"Von den unzähligen Klonen, die den 303-Sound imitieren, gilt die x0xb0x gemeinhin als einer der gelungeneren. In Form des x0x-heart Moduls gibt es ihren Sound nun auch im Eurorack."

Synthtopia Logo


"303 Clone For Eurorack Available For $303"

Sonic State

"A TB303 For Your Modular System"

Matrixsynth Logo


"Open Music Labs x0x-heart Eurorack Module Seeks Funding on Crowd Supply"

Beat.de Logo


"x0x-heart fürs Eurorack widmet sich alleine der Erzeugung zwitschernder Acid-Sounds, auf den Sequenzer im 303-Stil wird komplett verzichtet."

The Roland TB303 voice practically defined Acid music, heavily influencing the development of electronic music. Add that voice to your own setup with the x0x-heart Eurorack Module.

The x0x-heart module is the analogue section extracted from the x0xb0x (a TB303 clone) and made small enough to fit the Eurorack format. More nimble as a module, you no longer need to work within the constraints of the original TB303’s sequencer.

Product progression: TB303 -> x0xb0x -> x0x-heart -> xox-heart Module


  • CV control of frequency, gate, accent, slide, env-mod, decay, and cut-off
  • Switches for waveform selection (square and sawtooth), external/internal oscillator mix
  • VCA and VCF outputs
x0x-heart Front and Back


  • Eurorack standard format (3U height)
  • 18hp
  • ~1.75in depth (45mm)
  • +/-12V current draw 10mA
  • 5V current draw: 50mA
x0x-heart Side Angle

Hardware Build

  • Black anodized aluminum knobs with a diamond knurl pattern and two set screws (with slot heads and flat points)
  • A .063” (1.6mm) highly durable satin aluminum Metalphoto panel with a black print
  • Kit/assembled module includes 10” Euro power cable (16 pin to 10 pin connector)

x0x-heart Module Kit

Build you own x0x-heart Module using only through-hole soldering. All you’ll need is patience, and a soldering iron/solder. Tuning required.

  • x0x-heart PCB (SMD soldering done)
  • pacemaker PCB (SMD soldering done)
  • Grayscale front panel
  • 10” Euro power cable (16 pin to 10 pin connector)
  • Knobs
  • Switches, jacks, pots, headers, interconnect cables, nuts, washers, Euro mounting screws, etc.

Tuning/assembly information can be found at the Open Music Labs wiki: http://wiki.openmusiclabs.com/wiki/x0x-heart, http://wiki.openmusiclabs.com/wiki/EuroAdapter. Assembly video coming soon.

Open Source Hardware

To help you truly understand and control what you and your module is doing, Open Music Labs makes all schematic and board layout files available for your perusal and use.

Pacemaker (DIY version) source files http://wiki.openmusiclabs.com/wiki/EuroAdapter

Heart source files http://wiki.openmusiclabs.com/wiki/x0x-heart

x0x-heart All Pieces

About Open Music Labs

The goal of Open Music Labs is to create a central web location where people interested in using analog and digital audio equipment can go to find ideas, histories, parts, and like-minded others.

We want to create a resource people can use to share ideas and learn new things about hands-on audio creation, manipulation, and interaction.

Open Music Labs is a subsidiary of Flingco Sound System in Chicago.

2013 Flashback: a x0x-heart prototype - slaved to a TB303:

Special Thanks

Grayscale: Panel designer/manufacturer and all-around idea factory.

Tyler Thompson - T^2official: Video soundtrack artist and cool dude. His pro tip:

”Well my favorite thing about this module is how close it sounds to the real deal and I can sequence it with a less archaic sequencer. (I personally don’t gel with the x0x style sequencer.)

I recommend people pair it with a sequencer that has adjustable gate length per step like the Audio Damage Sequencer 1 or Industrial Electronics (Harvestman) Stillson Hammer MKII.“


Open Music Lab Logo

Open Music Labs

Analog and digital techniques - tools for musicians, composers, and tinkerers.



Front panel graphical designer

Metalphoto of Cincinnati


Panel manufacturer

RW Technologies US LLC


PCB assembler

See Also

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