"Moog" Eurorack Modules

"Moog" Modules.

A range of "Moog" style Eurorack modules to complement the Behringer "System 55". The general design philosophy behind these is:

  • "Moog Modular", but in eurorack format.
  • Modify the Moog designs only to correct errors.
  • Support the Moog Modular workflow
  • Panel aesthetic matches the Behringer “System 55” modules.
  • Use of through-hole components (where possible) and the standard eurorack power supply. 

I can supply panels for all of the modules below. These are 2mm aluminium, anodised black with natural aluminium graphics (all production panels include the vertical side "stripe" to match the Behringer System 55 modules) and are manufactured in the UK.

I try and keep a stock of the more popular panels - see below for current stock levels. Some panels are  "made-to-order",  the lead time for producing these is approximately 2-3 weeks.

If you require white graphics instead of natural aluminium, I can supply you with the FPD design files, and you can then order directly from Schaefer AG or a similar company.

Parts/components - I do not normally supply components or component kits, but if there is anything specific for these projects that you need please ask as I may have some spare in stock.

Note that some of these modules (those using rotary switches) specify PJ3410 jack socket. PJ301BM (also called "erthenvar") jack sockets cannot be subsituted as they have a different pinout.

PJ3410 v. PJ301BM sockets

901A Oscillator Controller and 901B Oscillator
901A panel

These are based on the original Moog modular VCOs from 1960’s, hence they are less stable and more temperature sensitive than the later (Moog 921 series) modular VCOs.

The 901A Oscillator controller and 901B oscillator must be used together.

  • The 901A contains a CV adder, plus an exponential converter. The Moog 901A has no front panel outputs, it has inputs only. 
  • The 901B contains a linear saw tooth oscillator plus wave shapers.




901B panel

Each 901A requires at least one 901B, but normally there would be more 901B (e.g. two or three or more) connected to each 901A. The approach of having a single exponential converter (901A) plus multiple linear oscillators (901B) in part contributes to the specific sound of the 901A/B combination.

I’ve added a limited PWM capability; with pulse width control inputs to the 901A and 901B that are not present on the original Moog circuit.

Each module is 8HP wide and 35mm deep.

The  Fitzgreyve implementation of the 901A and 901B is based on the circuits in the  “Technical Service Manual for Moog Modular System” dated April 1978, circuit references 993-042645 and 993-042646.

** This is a project for experienced builders **

901A Build document

901A PCB set (two PCBs)  GBP 16.00   (12 sets in stock)

901A 8HP Panel GBP 20.00 each (2 currently in stock, plus one "B Grade")

901B PCB set (two PCBs)  GBP 16.00   (15 sets in stock)

901B 8HP Panel GBP 20.00 each (6 currently in stock, plus one "B Grade"))


901A and 901B 

901A scale/tuning

951 and 952 Keyboard Interfaces.

The 951 and 952 provide CV control functions present in Moog modular keyboards as eurorack modules:

-          “Scale”: CV multiplier, from 0.94 to 1.06

-          “Range”:  adds or subtracts an offset to the CV ±150mV (approx 2 semitones)

-           Switchable exponential or LCR (“linear constant rate”) glide.

These are useful if using the 901A and 901B modules above, but can also be used with standard Behringer System 55 VCO modules. Both modules feature rear "bus/trunk" connections on molex connectors, that are overridden by the front panel jack sockets.

The modules can also be used to add a permanent offset to the incoming CV:  most Moog CV keyboards have 0V output at middle C, everyone else (mostly?) has 0V at the lowest key. The modules can be configured to compensate for this.


The 951 is a single channel module. 

951 Build Document

951 PCB  GBP 8.00   (2 in stock)

951 8HP Panel GBP 20.00 each (1 in stock)





The 952 is a dual channel module. To keep the uncluttered panel aesthetic, dual-concentric (aka "stacked" ) potentiometers have been used. Note that this approach results in a deeper module (60mm).

952 Build Document

952 PCB set (two PCBs)  GBP 16.00   (2 sets in stock)

952 8HP Panel GBP 20.00 each (2 in stock)


952 parts:

B500K Dual-concentric portamento potentiometer  (with 6.35mm knob adaptors) GBP 4.50 (2 in stock)

901 Voltage Controlled Oscillator.

Following the same design approach as Moog, the 901 Voltage Controlled Oscillator module combines the two "rear" PCBs from my standard 901A and 901B modules with a new single 18HP "front" controls PCB to give a single module oscillator. Includes fixed and variable level waveform outputs, a "mix" output (using an in-built CP3 mixer with selectable positive or negative output), plus a pulse width modulation input. Three PCB set, all through hole components.

** This is a project for experienced builders ** 

 901 Build Document 

901 PCB set (three PCBs) GBP 26.00 (out of stock, please email)

901 16HP panel GBP 34.00 (1 in stock)

CP3O (992)

This is a PCB for a Moog style “Control Voltages” CV switching and adder module.

The PCB was originally designed to make Moog style “console” panels to match the Behringer “System 55” modules. It can also be used to make an 8HP stand alone “992” module which is normally used  to control CV inputs to voltage controlled filters.

Moog modular systems use internal control voltage busses that are switched to control oscillators and filters. On this PCB, other than the “external input”, there are no front panel inputs or outputs:  all other inputs and outputs are on molex connectors on the rear of the PCB.

Fitzgreyve modules (e.g. 901A Oscillator Controller) already have the required input connections. A separate “universal daughter PCB” is available to assist with connections to Behringer modules.

Each module is 8HP wide and 30mm deep. 

CP3O-992 Build document

CP3O-992 PCB (Version 1 - 1 output)    Reduced price GBP 5.00 (6 in stock - this PCB is only available while current stocks last)

CP3O-992 PCB (Version 2 - 2 outputs)    GBP 8.00  (8 in stock)

992 8HP Panel GBP 20.00 (made to order)



This is a PCB that can be constructed as either a Moog CP3 (transistor based) or CP3A (IC op-amp based) 4-input mixer.

The PCB was originally designed to make Moog style “console” panels to match the Behringer “System 55” modules, but it can also be used to make a stand alone mixer module, as pictured.

Each module is 30mm deep. It is 24HP wide if used in a "console panel" (with an 8HP CP3-O PCB the total console panel width is then 32HP), and 16HP wide if used as a stand alone module. 

Build options:

  • For CP3 – click filter
  • For CP3 and CP3A – an additional performance control switch to enable channels 1+2 only, 3+4 only, or all channels.
  • For CP3 and CP3A – rear molex connector providing normalised inputs to the four mixer channels.

CP3-CP3A Build document V1-0

CP3-CP3A V1-0 PCB reduced price GBP 4.00 (only while current stocks last, 5 in stock)


The *new* V2-0 PCB corrects a couple of minor issues with the V1-0 version, and also allows the "+ Outputs" to always be uppermost if the PCB is mounted horizontally or vertically.

CP3-CP3A Build Document V2-0 

CP3-CP3A V2-0 PCB GBP 8.00 (14 in stock)

16HP CP3 or CP3A panel (as picture) GBP 34.00 (made to order)


901C "Output Stage"

901C panel

The 901C provides waveform amplification to allow a 901B (or 901) Oscillator to be used as a modulation source. It also generates positive-going and negative-going pulse waveforms (for "trills" etc.). There are two complementary outputs.

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

The original Moog module is rare - only about 15 were made.

The  Moog module used a 3-pole 6-way switch, which is expensive and not suited to the smaller Eurorack format. My design subsitutes an electronic switch for the output switching, all other parts of the circuit are as the Moog original.

Can also be used with Behringer 921B or 921 Oscillators!  

901C Build document 

901C PCB  Reduced Price GBP 4.00, or free with any order of 901A and 901B or 901 PCB sets, while current stocks last. (6 in stock).
(Note: the slots for the jack socket pins are not correctly cut, hence the reduced price offer. The build document shows how to modify the PCB.)

901C 8HP Panel GBP 20.00 (1 currently in stock)


1125 Sample-Hold Controller

The Fitzgreyve 1125 is a Eurorack implementation of the Moog “Sample-Hold Controller “ accessory.

The original Moog design has been used, but with the following additions:
- START and STOP input jacks, voltage triggered (V-TRIG).
- External Sample-Hold input jack, bypassing internal voltage sources.

The panel layout is intended to capture some of the “look and feel” of the original, in a Eurorack format.

In order to fit the circuit onto a single PCB, a “hybrid” construction has been used with some surface mounted components and some through-hole. Large (relatively speaking!) surface mounted components have been used.


1125 PCB  GBP 14.00 (none in stock - please ask)

1125 16HP Panel GBP 34.00 (out of stock, please ask)
Panel now comes with six free 3D printed ABS caps for the slide switches.
Parts for 1125:
CA3080 OTA Original RCA brand, new/unused old stock (NOS) GBP 4.00 each
1125 Video: 

1630d Frequency Shifter

This module could be considered a "cheat", as the module is a digital interpretation of the Moog/Bode 1630 Frequency Shifter module. For ease of construction and programming I have based this on a standard Teensy 4.0 processor module together with the Teensy Audio Board. A custom front panel PCB hosts these together with the controls and interface circuitry.

The original Moog module requires many careful adjustments, or close tolerance component selection, in order to operate successfully. I therefore thought that the digital approach was justifiable in this case.

Note that this is a "Frequency Shifter", not a "Pitch Shifter". 

There are some differences between the 1630d and the original Moog 1630:

  • The 1630d includes two audio inputs; the 1630 has only has one.
  • There is no dedicated “mix” output on the 1630d – the MIX output can be assigned to “OUT A” or “OUT B” (or neither)  using the “MIXTURE” control and associated push button.
  • The 1630d includes a “MIX CV” input that can control the content of the MIX output.
  • There is no “ZERO” position on the SCALE switch, as this is not required for the digital version. The switch position has been re-used to provide a 1V/octave calibration function (CAL) for the CV inputs.
  • The 1630d uses digital FIR Hilbert filters instead of the (analogue) "dome" filters used in the original. At low frequencies the digital filters are not as flat in their phase and frequency responses as the original analogue ones.
  • The software contains several user configurable options to tailor operation of the module to individual taste.

The module can be build using only though-hole components.

Some of the ICs have surface mount options instead of through-hole to ease component sourcing.

You will need to be able program the Teensy module using the open source software.


1630d Build document 

1630d PCB  Price GBP 12.00 (4 in stock).

1630d 14HP Panel GBP 31.00 (1 in stock)

1630d Video:



904C Filter Coupler

904C panel

This module must 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 modules to provide the 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 filter modules.

  • Also works if an AMSynths daughterboard has been fitted to the Behringer 904A LPF. 

    Full instructions are provided in the build document.

904C Build document 

904C PCB  Price GBP 8.00 (17 in stock).
904C PCB  Package (904C PCB + two Universal Daughter PCB) (6 sets in stock) Price GBP 15.00

904C 8HP Panel GBP 20.00 (4 in stock)
3P4W T18 rotary switch GBP 2.55 (1 in stock)
904C Video: 


991 Filters and Attenuator

The Fitzgreyve  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.

The filter cut-offs are 16 Hz, 41 Hz, 159 Hz, 482 Hz, and 1591 Hz, and each filter switch has a bypass position.

991 PCB Price GBP 8.00 (7 in stock)

991 8HP panel GBP 20.00 (1 in stock)




995A Reversible Attenuators

This module is a Eurorack implementation of the rare Moog 995A reversible attenuators, or “attenuverters” in modern terminology.

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

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

 The following build options exist when building this module:

  • Normalising of the lower two circuits to the input above.
  • Normalising the top circuit to a reference voltage, with various reference voltage options.

995A PCB Price GBP 8.00 (10 in stock)

995A 8HP panel GBP 20.00 (5 in stock)


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 or 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.

Thanks to Tom Wiltshire of Electric Druid for permission to use my modified version of his ENVGEN8C code as the basis for this, and to Jean-Pierre Desrochers for originating the original concept of building a “Moog” version.

911+ Build Document

911+ PCB Price GBP 8.00 (5 in stock)

911+ 8HP panel GBP 20.00 (3 in stock)

Programmed and tested PIC chip GBP 6.00 (2 in stock)

911+ Source Code (for personal non-commercial use only)


Triggered Controller

964 Triggered Controller
One of a number of custom modules that Moog made for the University of New York CEMS system in 1969.  Also known as the "one step sequencer".

The module generates three controllable output voltages actuated by either push buttons or V-trigger inputs.

This design is derived from pictures of an original module on the modularsynthesis.com website. The Moog PCB for this specific module has been modified to provide negative output voltages; the assumption being that as originally designed it generated positive voltages.

In my implemention, the output range for each potentiometer can be configured using jumpers.


964 PCB Price GBP 8.00 (7 in stock)

964 8HP panel GBP 20.00 (made to order - please ask)



A basic 3D printed  ABS "chicken head" knob to match those on Behringer modules.
These are designed to be a tight push fit onto T18 shafts - the first time you fit the knob the shaft will cut alignment grooves into the knob.

You will need to paint your own white line and any infill.

Chicken head knob GBP 1.00 each (3 in stock)


"Universal Daughter PCB" 

Picture of Universal Daughter PCB

This “universal daughter PCB” is designed to assist with connections to standard Behringer "System 55" eurorack modules.It uses the existing Behringer fixing points to mount on the rear of the Behringer module.

Moog modular systems use internal control voltage buses that are switched to control oscillators and filters. The Fitzgreyve CP3-O/992 PCB allows switching of control voltages to modules, but requires a connection to be made to the module(s) being controlled. Fitzgreyve modules (e.g. 901A Oscillator Controller, 904C filter coupler) already have the required input connections.

This PCB is primarily intended for used with 8HP wide Behringer modules:

  • 911 Envelope generator
  • 911A trigger delay
  • 904A Low pass filter
  • 904B High pass filter.
  • 921 Oscillator: The mechanical fixings are compatible, but the power “through” connection is not compatible.
  • Not compatible with the Behringer 992 (they put their power connector in an inconsistent position).

UD PCB Build document

Universal Daughter PCB GBP 5.00 (15 in stock)


"Ian Fritz" format Transistor matcher PCB 

Assembled PCB (parts not included)

Many of the above modules require transistors to be matched pairs in pairs. I have designed a small PCB for the "Ian Fritz Transistor Matcher" circuit with a standard eurorack connector. Allows for both ECB and CBE pinout transistors, NPN or PNP. There is no build document for this as information is freely available elsewhere.

Transistor matcher PCB GBP 4.00 (only available while current stocks last - 3 in stock)



Console panels

The CP3/CP3A and CP3-O/992  PCBs can be combine to make Moog style "console panels", but with the standard eurorack panel height.
Each Moog console panel would normally comprises a CP3 or CP3A mixer, a CP3-O (992), and a jack socket area. This results in a 32HP wide module which allows it to be positioned under a 901ABBB (or Behringer 921ABBB) oscillator set as in the full sized moog modulars.
The jack socket area can be used for multiples ("mults"), controller inputs or outputs, trunk connections, or anything you like.
I can design and supply custom console panels to order. The current price for a (32HP) console panel is approximately GBP 64.00

Example "Console" panel - CP3 with multiples.


Under Development:

912 Envelope Follower

902A Bandpass Filter Adaptor for the 902 VCA

 Future Concepts:

Real Ring Modulator. "Bode" style transformer based ring modulator, with input amplifiers and squelch.

Sequencer Controller. The "963" Sequencer Utility module from the University of New York CEMS system for use with the 960 Sequencer and 962 Sequential Switch.


For orders and enquiries, contact me at enquiries@fitzgreyve.co.uk

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