I got an idea of how to do that with the CD4017 when I was looking up schematics for building a Gate sequencer and a clock divider.
Essentially, how the module works is, you feed it a very high frequency from an oscillator. it creates a square wave version of the original signal and the 3 octaves bellow it. you can access any of the signals directly, or mix them via potentiometers to a mixed output jack.
Below is a schematic I drew up that shows the basic idea. This schematic only shows one sub-octave, not all three.
below is a drawing I made of the schmitt trigger used in the Yusynth 4017 clock divider. I used the same basic set up in my module also.
Below is some notes I made when working out which pins should be connected to each op amp. I also made a note to put caps on the outputs to keep the DC current from leaving the circuit.
This is the PCB I came up with. I threw in a picture of Brock Samson for good measure. most of the inputs and outputs are labeled on the pcb. The Transistors have "c"s on the pcb to indicate that is the pad for the "collector". The three unmarked pads in the center of the PCB are for the 100k trimpot used to offset the the square waves to make them AC signals. On the left near the bottom are the outputs for accessing each sub octave separately(the leads with the caps), and the sends for the mixer pots (the 10k resistor)
The pots (and pretty much all volume pots) should be wired with the "sends" coming off the 10k resistors the the Center of the pot. CCW pot lug should be connect to ground and CW pot lug should be connect to one of the pads labeled "return" on the PCB.
Below is a picture of my test circuit. usually these test circuits don't include all the features of my eventual modules, just what I need to make sure works....
This is a little video of me testing the circuit.
You may have noticed that this PCB has a lot of jumpers. Having a bunch of jumpers in your PCB looks hackneyed but this was the best I could do without having the PCB be double sided.
I created a panel design also, which I etched. this is lenna. If you want to etch this, make sure you invert it and flip in horizontally in photoshop, otherwise, it won't turn out like mine....
I didn't do a great job show how useful this modules is in my video. It makes a really awesome bass sound, like of like nintendo sounding.
All finished. email me with any questions.