Last night I finished the initial version of a sub oscillator PCB. It is based on the circuit in the previous post, but since I had one flip flop to spare I've included a two-octave down square wave as well as a 25/75-duty cycle pulse wave, similar to (and heavily inspired by) the Roland SH-101. The kind of square wave to output is selectable by a three position switch.
The board measures 30 x 100 mm, with 3 mm screw holes 4 mm from all sides, and should fit behind a 6HP panel. Cut-outs have been added near the input, output and switch connectors, to be able to mount the board with the components facing backwards and then route the cables to the front without adding any width to the module. This makes it possible to adjust the saw wave matching trimmer after the PCB has been attached to the panel.
The board has a slight shortcoming related to the pulse output - since the average voltage over one cycle is not 0V, the centering capacitor will not center the wave around 0V but slightly lower. This has no effect on the sound of the output but may lead to unwanted effects/clipping in subsequent modules/when mixing waves. I have still provided the pulse output as an option because it only requires two additional parts and may be useful to someone.