Wednesday 23 November 2022

Not "Black Friday" Sale

 The "not black Friday" Sale.

I'm clearing out some of my older projects, so it's "buy the panel, get the PCB for FREE":

Until further notice, all of the panels below now come with a matching FREE PCB:


100m-ish Modules:

  • 100m-ish VCO Driver  GBP 14.00 (3 in stock)
  • 100m-ish Audio Delay GBP 15.00 (9 in stock)
  • 100m-ish Ring Mod GBP 12.00 (1 in stock)
  • 100m-ish Signal switch Aluminium panel GBP 16.00 (7 in stock)
  • 100m-ish fixed HPF Aluminium panel GBP 12.00 (7 in stock) slide switches included
  • 100m-ish fixed HPF Black FR4 panel GBP 6.00 (8 in stock)  slide switches NOT included (see below)


Other Modules:

  • dAhDShR enhanced ADSR GBP 16.00 (7 in stock)
  • Transient/ dAhDShR Expander Black Aluminium Panel GBP 10.00 (8 in stock)


Useful accessories:

  • Slide switches for 100m-ish HPF GBP 2.00 for 2
  • Programmed PIC chip for dAhDShR GBP 6.00


Tuesday 6 September 2022

995A Reversible Attenuators


My latest module is a Eurorack implementation of the rare Moog 995A reversible attenuators, or “attenuverters” in modern terminology. This was suggested by a customer.

As far as I am aware, this was produced as a “special” for the Keith Emerson Moog Modular, and therefore only included in the recent "Emerson" reproductions.

The module uses my interpretation of the Moog op-amp based attenuverter circuit based on the  CP3A PCB.

Friday 2 September 2022

912 Envelope Follower development


Debugging of the 912 envelope follower is proceeding. I found a couple of minor errors in my PCB design (missing tracks!) that are easily corrected.

Once adjusted using the published Moog procedure, it seems to work OK - mostly.

The one issue I need to resolve is that althought the control output is fine down to 1mV RMS input signal, it becomes unstable when there is no input signal present.


Below are a couple of oscilloscope traces of the "control output" (upper) when the input is a repeating 250Hz sine wave envelope (lower).


I believe there is an error in the published Moog Schematic - the CL-1 diode in the trigger generator is the wrong way round ? With the schematic, the diode simply provides a path from +12V to 0V via R9A (330 ohm) - R9A just gets hot!

I believe the diode needs to be reversed, this is supported by pictures of actual Moog 912 units, where the diode cathode is clearly connected to R9A.

Sunday 28 August 2022

Another 904C Filter coupler video

Couple of videos of the 904C Filter Coupler in action, this time one built by a customer:


Tuesday 5 July 2022

Eurorack "Moog" Modular

Having started with "Moog" modules in eurorack just over a year ago, my planned two cases are now complete:

I orginally planned this as a Moog IIIC lookalike. I made the decision that the lower ("console") row would be normal eurorack height, not the reduced module height used in the original (5U high) Moog modular.

Key to modules: (B) Behringer, (F) Fitzgreyve, (A) AMSynths:

Top cabinet:
(B) 914, (F) 992, (B) 904A, (F) 904C, (B) 904B, (B) 904A with AMSynths daughter board, (B) 994, 2 x (F) 911+, 3 x (B) 902, (A) 993, (B) 911, (B) 911A, 2 x (B) 911.

Bottom cabinet, upper row:
(F) 901ABBB, (F) 901ABBC, (F) 901, (B) 921, (B) 995, (B) 960, (B) 962, 2HP Tune

Bottom cabinet, lower row:
2 x (F) CP3, (F) CP3A, (B) 923, (B) 961, (A) 924 mixer PCB with (F) panel.

The cases are recycled vintage mahogany. I've already got more modules than case space, so another case is being build. Not fitted, lying on top: (F) 991, spare (F) 901B, another (B) 921.

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 Oscillator

 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

912 Envelope Follower Investigation

 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

904C Filter Coupler

 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.


Tuesday 8 March 2022

 Panels have been delivered for my 901A, B and C (and also for my forthcoming 904C filter coupler):



Sunday 27 February 2022

I've just completed building the (originally rare) Moog 901C output stage. 
This amplifies standard Moog waveform levels for use as a deep modulation source, also generating positive-going and negative-going pulse waveforms. It has two complementary outputs.
As the original required a 3-pole 6-way switch, I've added electronic switching of the output waveforms, otherwise it's the original Moog circuit.
On the initial PCB run, the slots for the jack socket pins are not correctly cut, so I'm offering them at a reduced price (or free with 901A and 901B PCBs). The build document shows how to modify the PCB.
Works with my 901B oscillators, or with Behringer System 55 oscillator modules. 

A trial panel is on order.

Friday 25 February 2022

 901B Oscillator PCBs are back in stock.

The latest PCB version has some minor changes:

- C100 (470uF) changes from axial to radial, as radial capacitors are more easily sourced.

- new option to use a 3 pin "turned pin" socket (half of a 6 pin socket) for the "selected" transistors T7 and T10.

The build document has been updated (V1-1).

Sunday 6 February 2022

 Two videos of my 901A Oscillator Controller with 901B Oscillators, with temporary panel. 


General overview (the scaling of the 901A is not optimum in this):


901A scaling following adjustment:





Friday 28 January 2022

 Available shortly: DIY (do-it-yourself, build-it-yourself) "Moog" modules in Eurorack format to complement the Behringer "System 55 " modules:

- 901A Oscillator Controller

- 901B Oscillator

-- 992 "Control Voltages" (Control source switching and adder)

- CP3/CP3A Mixer - can be used with the "992" PCB to make console panels, or on its own.

- "Universal daughter board" PCB - to facilitate easy connections to the back of Behringer modules.

Under development:

901C Output Stage

-  904C Filter Coupler

-  901 Oscillator