Eurorack Neuron/Difference Rectifier PCB

This neuron was inspired by a paper on neural computing and is a variation of a typical analogue neuron circuit. It can be used as a complex audio waveshaper, gate or pulse generator, CV shaper or to generally screw things up.

This is for a PCB only designed for the Eurorack format.

Availability: In stock




This neuron was inspired by a paper on neural computing and is a variation of a typical analogue neuron circuit. To use it: put some LFO and/or EG signals on the inputs, or maybe something from a sequencer. Use the output to control pitch on a VCO or cut-off on a VCF – or anything else you can think of. Twiddle the pots until it sounds good. It will even work with just one input signal, although is much more interesting with two or three. It can also handle audio frequencies, so try it out as a wave-shaper. Feed it two or three signals from different VCOs and let them fight it out. Or feed it a VCO signal and a slow envelope or LFO to modulate the audio. Just some ideas, if you find some other uses, do share!

This circuit is slightly changed from the one on the double neuron PCB. The weight of the offset voltage is halved by the 200k resistor, this gives the pot a more useful range and limits the offset to VCC/2.

DIFFERENCE RECTIFIER This circuit is a hybrid of two basic op amp ‘building blocks’ – a difference circuit and a rectifier. Not sure if I have ever seen the two merged together before. It is probably a bad idea except for synth use, where it is a wonderful idea!

Basically the circuit compares the voltage on the ‘-‘ inputs with the voltages on the ‘+’ inputs. The difference between these voltages is fed to the outputs. If the difference is positive it appears on the ‘+’ output, if the difference is negative it appears on the ‘-‘ output. Again, a great way to mix boring CVs to get something interesting, audio frequency wave-shaping and it also can be used as a crude VCA.

Specs & Downloads

Specs & Downloads

Manufacturer Non-Linear Circuits
HP 8
Depth No
+12V No
-12V No
+5V No
Additional Resources Build Guide


Customer Reviews (1)

The Sounds = COOL. The Chaotic CV's = COOL. The Build = Red FlagsReview by Mr. Mojo Risin'
This module is a definite keeper even though the build is somewhat tricky. It produces some unpredictable patterns and adds some unique sound filtering. The build was extremely time consuming because of the layout. The only BOM and Assembly guide I could find on the Internet was for an older PCB version. A new guide would not be of much use anyway because there is some extra alignment required before everything will fit. With the exception of the six diodes, no BOM is needed because all of the part values are silkscreened onto the PCB. There are a few things about this build which you will need to be careful of:

1) The 3.5mm jack holes are designed for home-made 3-pin Thonkiconn jacks. If you try to use normal 3-pin Thonkiconn jacks, the holes are gigantic which creates a poor fit
2) Resistors, capacitors and the 10-pin power header soldered onto the flip-side interfere with the Thonkiconn jacks on the top-side. It's quite easy to cause short circuits unless the Thonkiconn jacks are raised slightly above the PCB before soldering them in place
3) The polarity symbols for some of the diodes are impossible to read. You'll need to visit the Muffwiggler build thread at for an image posted there to see the correct orientation. There are two diodes marked 400x. I used 1N4001. The other four diodes I used were 1N4148 which I had to guess were correct(?) after reading the older Assembly Manual.

The panel I purchased was the special edition Modular Addict version. Instead of a regular aluminum or fiberglass panel, this one has a decal pasted on top of an aluminum panel. It certainly fits in nicely sitting next to all my other mis-matched panels ;^)
Unique Sounds And Chaotic Patterns: A+
PCB Design And Assembly: C- (Posted on 8/21/2017)

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