My strip board version, and also my re-implementation on a bread board was only a partial success. I found that the low pass filtering works fine, but that it always self oscillates ! This only stops when disconnecting IC1b pin 5. I’m wondering whether the 1Mohm resistor R23 or part of the rest of the circuitry picks up some noise which puts it into self oscillation.
So my question is:
Is anyone familiar with this filter / schematic and possibly has anyone gotten this to work?
That layout is from the same Electro-music thread, and posted by the same individual, as the error-ridden Wave Animator layout discussed here. Odds are it’s also wrong, I’d say.
The thing is that I got the schematic from Yusynth.net and I followed the schematic alongside the strip board version and they match (unless I’m repeatedly overlooking the same thing).
So I’m wondering whether the schematic is flawed. Specifically the feedback bit which was added to the original publication by Steiner.
I send an email to Yves Usson about this, but he never replied.
" The filter was re-designed by Yves Usson (YuSynth) to do away with some of the erratic behaviour of the original design, but I noticed he didn’t manage to get rid of it completely. The resonance can give a very loud whistle and if you turn it past that, with cut-off freq turned down, the filter stops working with a deep pop that can’t be good for the speakers. I’ve included a 5K trimmer to replace the 3K9 resistor, R18 in the schematic, so I can set the reach of the Resonance control a bit better. This works up to a point but it’s not possible to tame the resonance completely this way. The resonance gets better as you reduce the resistance of the trim pot but this reaches zero Ohm before resonance is completely tamed. But then again, that’s the character of this filter so you don’t want the agressive behaviour to disappear completely "
For the benefit of future readers of this topic (future me, perhaps) there were several posts in another topic about the resonance problems with this filter, starting here:
