993 Trigger & Env Voltages

AMSynths 993 Panel

Introduction In August 2020 I bought a set of Behringer System 55 modules, as my first journey into Moog modular. My plan is to recreate the Klaus Schulze IIIP synthesizer and Dual Sequencer setup that Klaus bought on 22nd December 1975, and used successfully for many years.

Whilst the Behringer modules cover most of the Moog modules I need, there are a few additional modules I need to recreate, like the 993 from the IIIP.


AMSynths 993 Module This is a replica of the original Moog design but without the colour illuminated slide switches. Even Moog could not find these when they re-issued the System 55 and had to have them 3D printed. I have used black DPDT slide switches, which switch on the circuits as well as an indicator LED.

I have used red LED’s for the Trigger Inputs, yellow LED’s for the trigger routing, and green LED’s for the 911 to 902 routing. They are cylindrical LED’s mounted on standoffs, which match the Behringer SMD LED’s. I did experiment with white LED’s but they were not truly diffused and had a center bright area.

Cabling Diagram – Left

The AM993 PCB has a 12V power inlet socket, eight DPDT slide switches and eight LED’s. Rather than hand wiring to each jack socket, I have used a more robust cabling system that uses Molex “latching” 2 and 3 pin connectors.

There is a small daughter PCB that attaches to the back of each of the 902, 911A and 911 modules. The pictures show the cabling at the rear of the modules. A 994 Dual Multiples module is used as the input for the two S-Trig signals to the 993, the Upper set of multiples is connected to Input 1 and Lower to Input 2.

Cabling Diagram – Right

Molex connectors are used to provided the inter module cabling, with wires soldered to the various Behringer jack sockets from the daughter PCB’s. The jack sockets are not normalised, so no PCB traces need to be cut on the Behringer modules.

Confusing Lettering The original Moog 993 panel lettering is slightly confusing, and the AM993 uses the exact same lettering – sorry! The switch to control S-triggers to the left hand 911 envelope generator is lettered as “From 911A Input”. In fact its a trigger output direct to the left hand 911, which does not go via the 911A trigger delay. “To 911 Left” would be a better lettering!

No Normalisation Because the Behringer modules lack any jack socket normalisation it is not possible to connect a jack plug into the 902 (lower CV input) or 911 (S-Trigger Input, CV Output) and break/override the connection to the 993/911A. The connections between the 993 and 902/911/911A should be disconnected by turning the appropriate 993 switch to OFF, and this is how I recommend using the AM993 in a modular system.

If you need to use an external patch cable, for example when using the module independently, then put the corresponding switch to OFF. The 902 uses the lower jack socket as the 993 CV input, so there are two “free” CV inputs that can be used alongside the 993 control signals.

AM993 2022 Edition The module has been upgraded to include a 6-way IDC socket which enables connection to the internal AMSynths control bus, which carries three sets of Pitch CV and V-Triggers. The AM993 can then select from the V-Trigger signals, which are converted to the required S-Triggers. The right hand slide switch has three positions (Bus 2, Bus 3, OFF), to enable all three triggers to be selected from. This also negates the need for an AM997, and an AM990 module is used to patch external CV and gate signals into the control bus. The 2022 Edition also uses 6-way IDC cables to connect to the 902/911/911A making installation easier.



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