Saturday 18 September 2021

Behringer 904A filter with the AMSynths daughter board installed - this swaps out the Behringer capacitors for matched lower value polyester capacitors as used in the late 60's Moogs. 

Took about an hour to convert - most  of that time was spent removing the original Behringer capacitors (they are thru-hole, the rest of the Behringer circuit is surface-mount). Just used solder sucker and braid - no fancy desoldering station needed.

This now sounds very very nice!

Thursday 16 September 2021

 Just arrived - my first two "Moog" PCBs to complement the Behringer System 55 modules.

The left hand PCB is the "control voltages" section of the Moog CP3/992 modules - this can be used as part of a Eurorack CP-style module, or for a 992 Control Voltages module to drive the 904 series filters. Note that my PCB differs from the Behringer CP3-O and 993 modules:

1. There are no front panel inputs or outputs - the PCB is designed to support "Trunk Lines" as in the original Moog Modular, but using Molex connectors on the back of the PCB.

2. The "Ext Input" is an attenuverter  (or "Reversing Attenuator" in Moog-speak): Moog and Behringer have an attenuverter on the 992, but only an attenuator on the CP3-O. I've also added the option to normalise the Ext. Input to +6V - useful for switching in pre-set transpositions etc.

On the right is a dual purpose Mixer PCB that can be configured as either the CP3 (transistor based), or as the CP3A (op-amp based). The PCB supports the "click filter" for the CP3 option (missing on the Behringer CP3A-M module!), and optionally a performance control (SW2 on the PCB) to mute channels 1&2 or channels 3&4. I will be combining both of these PCBs behind a panel to make "CP3" modules, but the Mixer PCB can also be rotated 90 degrees to form a stand alone (16HP) mixer module