Tuesday 14 December 2021


 My prototype Moog 901B in 8hp of eurorack. 2 PCBs, all thro' hole. The rear PCB holds the oscillator, the front PCB holds the sockets, pitch control, range switch and range caps (plus an op-amp as I've added a PWM input).Two Molex connectors on the rear are for the "bus" from the 901A controller, plus one with all of the outputs on it.

The extra pot and wiring in the pictures is because there is (as yet) no 901A controller - the design for the 901A is ready, but no point in proceeding with it until I had a working oscillator!

The output:

(any glitches visible on the triangle and sine are because I don't yet have all of the range caps installed - these are also used for filtering the triangle waveform).

While the prototype uses thonkiconn jacks, I'm swapping it (and the 901A) to use PJ3410's, as the Alpha rotary switch sits higher on the PCB than I had originally envisaged. I could also do with using a longer shaft pot for the pitch control.


  1. Hello!! This looks amazing!!! WHat a great project!! A little note: I remember seeing an original 901 Sine & triangle waveshapes & they both had a little 'glitch', WHICH ACTUALLY is fantastic, for they added the amazing --different, not "super clean"-- sound that makes the 901 SO INCREIBLE!! Please consider this AS A PLUS, not as a defect!!! Blessings!!

  2. The glitch originates from the sawtooth to triangle convertor, and is normally adjusted out. However, it can always be adjusted "in" !