912 Envelope Follower

 

This is a Eurorack implementation of the Moog 912 Envelope Follower and trigger extractor.

 

The Moog circuit is designed to work with input signal levels nominally around line level (up to 1.4V RMS) although it will process up to 4V peak-to-peak  – if using Eurorack level input signals they will probably need to be attenuated.

 

The module is unusual in that the CV output is logarithmically scaled - it increases by 0.5V for a doubling of input signal amplitude. 

 

I've added a V-TRIG output, and some optional additional output buffering. 

  

This one has been on and off my workbench for about 4 years. The Norlin 1979 Schematic (Moog Modular Service Manual) contains a number of errors and inconsistencies, and I encountered some instabilities in the circuit that needed to be resolved.

 

Calibration was also a problem until I recently found the key information from the 1981 Moog Modular Users Manual  "Control voltage drops rapidly to -4V at levels less than -60dB" - hmm, shame they don't mention that in the service manual.

 

Video: 

 

Please note while the build for this module is relatively simple, it can be very tricky to calibrate. I'll try and do a video of the calibration process soon.

 

 

"Moog" LFO, and Ribbon Controller PCB

 Two new offerings:

First, we have a simple triangle/square LFO module, inspired by those in Keith Emerson's custom Moog Modular - complete with "repurposed" 902 panel and "dymo" labels.

 -          Outputs:

o   Triangle: ± 3V

o   Square: ± 4V

-          Typical Frequency ranges:

o   Low range: 0.06 to 2.5 Hz

o   High range 0.2 to 17Hz

o   Use of the CV inputs will extend these up to approx 35Hz

 Range etc can be tailored by the builder. 

 (See "Moog eurorack module" page)

   

Secondly, a  basic analogue ribbon controller, originally designed to go with my Eurorack “moog” system. It is designed to use a Spectra Symbol linear “softpot”, with an optional Interlink electronics pressure sensor (FSR).

This is a PCB only offering (no panel) as it is designed to be built into a housing of your choice.

 Features:

-          Constant current ribbon drive (supports “hammer-ons”).

-          Position CV output

-          Gate (Moog “V-trigger”) output

-          Moog “S-trigger” output

-          Support for optional pressure sensor and pressure CV output

 ( (See "Utility PCBs" page)

 

 

 

992 to 904C

 I've updated the 904C build manual (V1-3) to include more info on connecting a 992 "Control Voltages" module to the 904A and 904B filters when a 904C is also connected . This now covers the Fitzgreyve 992, Behringer 992, and AMSynths AM992.

Free 100m-ish Analogue Delay panels

I've recently tried to get a colour match to the grey Behringer 100m panels. This has resulted in a lot of spare "100m-ish Analogue Delay" panels that are "not quite right". I'm giving these grey panels away free if your purchase an analogue  delay PCB - select "lighter" or "darker" but otherwise it's my choice. 

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