From thread on muffwiggler:
I keep getting asked about these so have sent off a design for a pcb containing 1 of each of these circuits.
The Difference Rectifier has 4 inputs (two + & two -) and two outputs. The Neuron has two inputs and one output. There is a pad labelled 'ext' where extra inputs can be added if desired (use a 100k resistor attached to the jack).
All inputs for both circuits can be wired to attenuating pots if required. The two pots on the PCB are the critical Offset and Invert controls for the Neuron. The Offset is slightly modded from the previous Double Neuron PCB as it now ranges between +V and -V and its effect is halved by the 200k resistor to give greater useful range.
Schematics and demos - Difference Rectifier and Neuron
Build manual pdf
The PCB is small so will suit Euro builders. Approx 1.5 by 2 inches.
The 2 board mounted pots (both 100k) are 1 inch apart, the idea is to mount the PCB to the panel with threaded pots. There are 2 mounting holes otherwise if you want to attach the board some other way.