Crux DIY VCA Kit

The River Synths Nucleus DIY VCF is a dual voltage controlled amplifier with a discrete OTA core

This is a full kit set in the Eurorack format. Most components have been pre-soldered as SMT parts!

Availability: In stock





  • Dual VCA around discrete transistor OTA core
  • Switchable linear or exponential VCA response
  • Switchable between Audio (AC) and CV (DC) use
  • Starts to pleasantly saturate beyond levels of 10Vpp (clips at 20Vpp)
  • Envelope (unipolar) and modulation (bipolar) CV inputs
  • Smart normalization of unused envelope inputs to allow for full-range bipolar modulation






From River Synths:

After overlooking VCAs for many years, I began to appreciate the huge range of functions they can serve up. They’re really everywhere, in simple loudness contouring circuits, tremolo effects, tone controls, filters, overdrives, mixers, amplitude modulators, panners, cross-faders, and CV performance controllers. I also learned that VCAs put their subtle signature on the overall sound of an instrument.

The VCAs in the Crux are built around newly designed operational transconductance amplifier (OTA) circuits, built from discrete transistors. If you need a super-accurate VCA, this is not for you. However, if you appreciate the warm and lively nature of discrete electronics, the Crux will serve you well.

A phrase often used among modular musicians is “you can never have enough VCAs”. Probably followed by “I need more rack space”. That’s why the Crux is a compact module, simple and straight, a short signal path, and no frills. As there are no frills, there’s little fancy text here. It can do what a VCA does. It can do it twice. It can do it linearly or exponentially, and does it on audio or CV. And that’s it!

Specs & Downloads

Specs & Downloads

100 River Creative
HP 6
Depth 32mm
+12V 23mA
-12V 23mA
+5V 0mA
Additional Resources Build Guide


Customer Reviews (1)

AMAZING VCA!!!Review by Shay
The building process was very simple, few sockets and buttons on the pre built SMT board.
the VCA sounds AMAZING, very fast and punchy with warm sound. (Posted on 6/18/2017)

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