I’ve just finished building a Polivoks filterboard and the filter cutoff is not doing anything at all.
No sweep, no attenuation, the sound comes out as it goes in.
The weird thing is that the resonance seems to work fine as I can hear the volume dip and the sine-y tone as I turn it up.
All the parts are from mouser and I’ve built quite few shruthi boards over the years which worked as soon as I plugged them in so the only thing that could go wrong is the lm4250.
I got 20 of these chips from a russian eBay seller and they’re marked “1407”.
They seemed more trustworthy than the chinese equivalents.
Tried every single one of them and I always get the same behavior.
Maybe this IC is not a straight replacement for a LM4250?
I’ve never worked with this chip before but I understand it needs proper current biasing to work.
Anybody has any suggestions?
I can probably get a NTE888 from a reputable source, but I’m a bit unsure if this IC requires any resistor changes…