Noisy 12dB SVF

Paco · Posted: Tue Sep 28, 2010 8:51 am Post subject: Noisy 12dB SVF

Hi

I built this module some time ago and I can hear a kind of pink noise at the outputs, specially with the cutoff widely opened. This was described before on this topic, and there are several workarounds without success:
http://electro-music.com/forum/viewtopic.php?highlight=noisy&t=18929
So it seems to be a common issue of this VCF. Did anybody find a solution? Any ideas?

Nothing is wrong on the PCB at first sight, and I have already replaced all the IC's but still the same.

I've also observed with an oscilloscope that the outputs are inverted, I get a sawtooth coming from the LP out while there is actually a ramp in the VCO. Is that the way it is supposed to behave?

Thanks in advance, I will keep on researching

synthmonger · Posted: Sun Oct 17, 2010 12:06 pm Post subject:

I'd guess it's the LM13700. Those old OTAs can be a bit noisey when you're not feeding them hot signals.