I had a go at the SubOsc on a bread board and liked it so much that I thought I’d turn it into a module. Since I use EuroRack I thought that one SubOsc would be a waste of space so why not make 2? Well, it happened that I could only find one 4013, so I had to look for alternatives. Luckily I found 2 dual JK flip flops (4027) so I decided to use those. This meant that I had to alter the schematic a bit, but I got it to work exactly in the same way. I’m including the schematic here which firstly shows the original schematic with the 4013 and the output calibration I posted about earlier and secondly shows the alternate version based on the 4027. The asterisk marks the point where you pick up the pulses from the synth which you can either feed into the 4013 or the 4027 circuit part. For the transistor I used a standard BC547, but any plain NPN transistor will do.
Note, pin 14 of the 4013 should be connected to Vdd (+), I forgot to draw this in the schematic.