So I build the SubOscillator some time ago.
As I had room for 2 on the same board (SubOSC for Crave and other equipment) I build 2 but lacking a second CD4013BE finishing the second suboscillator had to wait. So after a while I received the 2nd chip (Mail Day Thread) and this week I added that to the circuit. Alas it turned out the 2nd sub oscillator didn’t work.
[debug mode on]
1: I checked the 2nd instance of the suboscillator circuit comparing it with the 1st and couldn’t find a difference.
2: I checked all power connections. All voltages were according to what I expected.
3: I tried the chip from the first sub oscillator in the 2nd and experienced no joy.
4: I tried the chip I had put in the 2nd sub osc in the first sub osc to see whether it was still alive and to my great surprise it didn’t produce a signal but worked when I touched the resistor in the feedback loop /Q -> D with the tip of my oscilloscope probe.
I then found that I could get the 1st circuit to work for this chip as well after adding a small capacitance to ground ( which my oscilloscope probe was doing as well ).
But of course this left me puzzled. Why would the one chip work without any problems while the 2nd one needed this capacitance? Because the chips were made by different manufacturers I attributed the difference in response to that.
[debug mode off]
[resolution mode on]
Then I discovered that both instances of the sub oscillator lacked one essential connection. The GND pin of the CD4013 had not been connected ! After remedying that, all worked well.
Problem solved.
[resolution mode off]
[flummoxed mode on]
But why did the 1st sub oscillator work at all when it also was lacking this seemingly essential connection? Maybe it was ‘naturally grounded’ ?