I just finished my implementation of the sub oscillator in eurorack format. Since the circuit is only small I decided to build 2 in one module. In a previous post I wrote that a JK-flip flop of type 4027 should be equally usable for this purpose (as I did only have one 4013), and this worked on my bread board, in the end my version showed some instabilities which I can not explain, other than maybe that I have no idea where I salvaged the ICs from and whether they were trustworthy to start with. So I decided to go with the 4013 and order a few more.
I added a little something to the design though. I thought it would be useful to be able to “see” that the cable connected to the module is indeed feeding a signal into it. So I added a PNP transistor and a LED to the circuit. The base of the transistor is connected to the collector of the NPN transistor in the input circuit. So the schematic looks like this now:
Because the input transistor’s collector is always high if there is not input signal, a negative pulse will indicate that there is an input signal, hence the choice of a PNP transistor (center of diagram) to control the LED. You can also use a BC558, BC559 or whatever small signal PNP transistor you have lying around.
Next I printed a panel, like the one in the following picture:
Apart from a few holes this panel (middle, left) contains 2 low structures ( for lack of a better word ) which can be used to hold a circuit board. Hot glue is your friend!
And finally a front view of the SubOscillator module:
The device sounds really nice, so I’m glad the SubOsc reference was posted on this forum.