6401 Ring Modulator

The  6401 is a Eurorack implementation of the Moog Bode 6401 Ring Modulator.

The core ring modulator circuit is passive, using diodes and transformers.

The balanced output circuit has been replaced by a CP3 mixer circuit, which also enables the input signals to be mixed with  the modulator output.

 Build options:

-          The full circuit

-          Omit the squelch (noise gate) circuit

-           As a “passive” ring modulator only

Due to the small size of Eurorack modules, it is not possible to accommodate the originally specified transformers (even if you could find them!).

A choice of two types of transformers is supported depending on available budget: Edcor (as pictured), or Xicon (limited bandwidth).

The build is not difficult, but if the squelch circuit is included, component placement on the main PCB is dense to fit everything in, so accurate soldering is required.

If anyone wants to do a build using Xicon transformers,  I'll supply a free set of PCBs in return for photos of the build.

Depth behind the panel is approx. 40mm, this is heavy - 8oz / 250g. 

Hacking the M5Stack MIDI module, a cheap SAM2695 General MIDI module

 

Where I have needed a General MIDI chip (GM module and CV-to-MIDI) , I have previously used the S2 waveblaster module from Serdaco BV, but with a little work the M5Stack module provides a more cost effective approach.

 

The SAM2695 is a very useful 64 voice General MIDI IC with built in effects. It uses a 6mm square 48 pin QFN package with 0.4mm lead pitch, which is difficult to solder by hand.

 

The M5stack MIDI module provides a source of a pre-soldered SAM2695 with a TTL level MIDI input, but needs some modification to get external audio outputs.

 

Video 

 Instructions PDF