[sdiy] 3320 as SVF

[Tony Allgood]

Harry wrote: I built the data sheet version... no bleedthrough problems
for me.

OK, so I pulled the OB-Sx apart and had a look more closely. And I found
it. The 3320 is oscillating at approx 300KHz when you take the cut-off
frequency above 12KHz or so. Resonance will reduce the oscillation. It
seems that the input stage of the 3320 is honking merrily away at
certain levels of CV.

So after spending most of this morning trying to find out why it is
oscillating, I'm giving up. My bets are that it is a bad 3320... but
since I didn't have another one to check, I bunged a 22nF cap slap bang
on the input pin and ground. Ha... now it works perfectly. But if anyone
has a spare 3320 they want to give/sell/swap then feel free to get in
touch.

Regards,

Tony Allgood  Penrith, Cumbria, England

Oakley Modular Synth and TB3030:
www.techrepairs.freeserve.co.uk/projects.htm
My music: www.mp3.com/taklamakan