Digisound 80 filter

Hi all,
I have finished building the digisound 80 filter using the schematic from @EddyBergman website.
It worked first time (amazing feeling) but I can’t get it to self oscillate.
I didn’t get a chance to play with any of the trim pots but it does not look like that would have helped me anyway.
It almost feel like the self oscillation is only few volts away.
Do you think that swapping the R6 51k (connected to +15v ; I am using +/-12V) for a ~25k would sort it ? As it is working great at the moment I don’t want to break it by doing something stupid.
Thanks !

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I’m not sure if you have a 1V/Oct signal on the appropriate input but if so try disconnecting it. That input should actually have some attenuation on it. If you can’t get self oscillation it is usually due to too high audio or CV input level. You can try a lower value resistor for R6 without any problems. In fact I don’t know why that external resonance input is in there. I never use it. This filter is rather touchy with tuning. You should try tuning trimmer RV7 too. But nothing will break if you experiment with changing resistor values on the inputs.


Thanks for the reply. I’ll try this. And you are right, the sound of it is very characteristic, I really like it.


Yes it’s really is a very good sounding filter but not the easiest to get right with tuning. I’ve had my fair share of troubles with that too. If you haven’t already, you should also try building the Steiner-Parker filter. That’s a real favourite of mine too.


Got it working fine !! Thanks.