Another 904C Filter coupler video

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

 

 

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.

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.

 

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. 

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. 

 

 I have now created a video of the 904C filter coupler:

 

 

 

 

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:

(Source 912 PCB pictures taken from https://modularsynthesis.com)