Patch Chord

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  • $ 430

Erthenvar Patch Chord - a bank of 25 "Oscillator Controlled Oscillators", which can be used to generate chords in a Eurorack system.

2017.04.16 - Out of stock and not planned for another run

All Patch Chord modules shipped on July 28th, 2013 and later have V3 firmware!

This page has NOT been updated for V3 yet. See this blog post for details.

The Patch Chord continously samples the cycle duration and duty cycle of the input waveform. It outputs 12 semitone steps above the input note, 12 semitone steps below the input note, and the root note itself (available from two output jacks). All outputs are pulse waveforms with continuously variable pulse width.

An oversized tri-color LED spans the color spectrum in each octave, so each note has a unique color! The input jack is passively multipled to an output jack so the visual effects of the LED can be had even if the module is not part of the current patch.

There four modulation types available, each with an input jack and a three-position switch. The switch can turn off the modulation, allow the CV value to control the parameter, or turn on the modulation. The modulation jacks are all DC coupled and respond to audio rate signals, though the tracked waveform has a lower limit of around 20 seconds per cycle.

  1. The SQR modulation forces the tracked duty cycle to 50%, making all of the 25 outputs into square waves
  2. The INT modulation changes the relationship between each output from a semitone step to an integer or harmonic step
  3. The ZERO modulation resets all of the output counters to 0, similar to a sync function
  4. The HOLD modulation stops tracking the input and keeps the last counted cycle duration and duty cycle values

This module requires +5V from the bus board! We offer the freelunch as a +5V solution.


  • Eurorack power cable and M3 screws are included
  • A total of 25 oscillator outputs tracked from 1 input
  • RGB LED with color-per-note functionality
  • Four "ACV" audio rate CV inputs
  • C&K switches



Eurorack horizontal pitch 22 HP
Depth 60 mm (2.36")
Maximum Input Current (+5V) 65mA (version 3 requires 100mA)
Maximum Input Current (+12V) 65mA
Maximum Input Current (-12V)           65mA
Input Impedance 112kΩ
Input Threshold 600mV
Output Impedance 1.2kΩ
Output Swing +/-5V


User Guide

Patch Chord User Guide


Patch Chord YouTube Playlist