Sunday, 3 July 2022

911+ Envelope Generator


The Behringer 911 Envelope generator is excellent value for money, but suffers from difficulty getting values at the extremes of control travel due to the use of budget potentiometers. This is particularly a problem at the low end of the T1,T2, T3 controls which leads to difficulty in setting short envelope times. The panel control values also do not generally match the actual envelope times.

This module is designed to address the above issues, add some additional functionality (looping modes, linear envelopes, "Punch", Time and Level modulation), while maintaining the Behringer System 55 “look and feel”.

The Fitzgreyve 911+ uses nothing resembling the original Moog circuit, being based on a PIC microcontroller. Single PCB, all through-hole components.




ADR envelope in LFO mode.


Tuesday, 21 June 2022

991 Filters

Our latest "Moog" module for eurorack:

The  991 Filter and Attenuator is a passive module (i.e. no power required) that contains a switched low pass filter, a switched high pass filter, and an attenuator.

Single PCB with easily obtainable compoenents.

May be built using vintage Mullard C280 aka "tropical fish" capacitors (as in the picture below), or with smaller modern capacitors. 

Friday, 3 June 2022

901 Voltage Controlled Oscailltor

 Originally it was not my intention to build this module, but having got the 901A and 901B working this was more of an academic excercise to prove that following the Moog approach of combining a 901A and 901B in a single module actually works.

There is no Moog documentation for the 901, so some educated guesses have been made.

The 901 Voltage Controlled Oscillator module combines the two "rear" PCBs from my standard 901A and 901B modules with a new single 16HP "front" controls PCB to give a single module oscillator. 

It includes the same fixed and variable level waveform outputs as the Moog original, but I have added a "mix" output (using an in-built CP3 mixer with selectable positive or negative output), plus a pulse width modulation input. 


Tuesday, 17 May 2022

Wednesday, 20 April 2022

 While I'm waiting for delivery of  the PCBs for my next two "Moog" module projects (991 passive filters, and 911+ envelope generator) I thought I'd take a look at the 912 Envelope follower module.

It seems simple enough, but will need probably need two stacked PCBs as it looks too much for a single PCB. Controls and trigger extractor on the front PCB, envelope follower circuit on the rear PCB.

The obsolete diodes will need some investigation. There is one resistor marked "25" on the Moog schematic. Given it's position I think it is "R25" not "25 ohms". I've overlayed pictures of the top and bottom of the original Moog PCB to try and identify it:

Moog 912 PCB
(Source 912 PCB pictures taken from

Tuesday, 12 April 2022

 Now available, my latest "Moog" eurorack module: the 904C filter coupler.   

This module needs to be used with a standard Behringer 904A low-pass filter and a 904B high-pass filter, and gives band-reject and band-pass modes.

8HP, single PCB design with easily obtainable through-hole parts.

The Moog module used a 3-pole 9-way switch, which is expensive and not suited to the smaller Eurorack format. My design subsitutes an electronic switch for some of the switching, other parts of the circuit are as the Moog original.

Some soldering is required to the Behringer filter modules to provide the input, output and CV connections to the 904C:

  • Inter-connections to the 904A and 904B can be made easier using Fitzgreyve “Universal Daughter” PCBs.

  • No soldering is required to, or near to, any surface mounted (SMT) components on the Behringer modules.

  • Full instructions are provided in the build document. 


    See the "Moog eurorack modules" page for details.  
    Demo video coming soon.


Wednesday, 9 March 2022


I can now supply panels for the standard 8HP "Moog" modules: 901A, 901B, 901C, and 992 (see the "Moog Eurorack Modules" page).

These are high quality 2mm anodised aluminium in black with silver graphics (including the side "strip" to match Behringer System 55 modules).

Panels are made-to-order, the lead time for production is normally 2 weeks.


If you require white graphics instead of silver, I can supply you with the FPD files, and you can then order yourself directly from Schaefer AG or similar companies.