I’ll try tracing some more tonight after I make this update to mine.
Here’s a demo. My resonance control is the bottom one. I love the sound of this thing!
Bandpass fixes v3 https://www.youtube.com/watch?v=sNTYHaqJqpc&feature=youtu.be
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Awesome! Mine is working as well. To make the resonance change more dramatic, switch the 4k7 resistor for a 1k.
Great! I’ll give that a try.! Would I be crazy to say that if you were to replace the 15k resistor from diodes to ground with a trimmer pot, you could dial in how you want the res control to work. How much res at full etc. I may give that a whirl too. I’m working at a similar filter right now which has basically the same setup. The trimmer pot really lets you fine tune it.
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I have no idea if that would work, but I hope so. Go for it 
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Here’s a quick demo. I apologize for the ambient noise. I recorded the audio separately, but something went wrong with that, so it’s just the audio from my phone.
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Hi, Just built this and plan on building 3 more to try and get a (very simple and probably not very effective) vowel (formant) filter.
Could someone explain to me (reeeeeally simply i.e. put this wire here and that one there) how i can add Cv control using vactrols?
Also, doe’s anyone know if the resonance can be tampered with so its a bit more squealy?
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This could well become the catchphrase of this forum.
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That should do it. You could also try going even lower.
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4:05 onwards for how to add vactrol. Add 2, one between leg 1 and 2 on knob1 100k and another also between leg 1 and 2 on knob2 100k.
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I’ve just spent hours looking at the schematic, I think I’ve cracked it. Knob1 100K 1 should be 2&3, 2&3 should be 1. It’s made mine much much more like the real thing, The res is still an issue though but I’m working on that.
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So I think the wiper (middle pin) of the res pot is supposed to be coming off the bottom row of the diodes too.
the sounds quiet at full res though, sounds ace
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Sweet! I still felt something wasn’t right. Think you could edit the stripboard layout with your findings?
Yeah I will a bit later. 
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I swapped them pins round on knob one, idk if its just my circuit but knob one doesn’t do much anyway except over a tiny range.
I’ll have a look at mine later and put a drawing up
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so, Ive swapped the knob1 and 2/3 around, taken the res wiper from a different place, moved the jumper to pin 5 of the chip (like said previously) and that should be all good. I did change the 4.7k resister to something under 1k.
I also used a stereo pot for the cutoffs as I think its much easier to control and the sweep is much nicer.
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Can’t wait to try this! Just for completeness, your image doesn’t have the fix from @lookmumnocomputer implemented. Great sleuthing, though!
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Yeah that fix is wrong! I’ve done that on purpose
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Think of a vactrol as an easy way of controlling a variable resistor with voltage, so anywhere you see a potentiometer with one end connected to the wiper you can substitute with the resistor side of the vactrol. On the LED side, you can plug a cv signal directly to it as long as you protect it with a resistor (~180ohm) in the circuit.
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