Score one for @BlackDeath. I inspected the chips and realized had used an LM324 instead of TL074.
It’s still not behaving as expected but the high pitched ringing is gone, so thats a step in the right direction.
Resonance pot seems to just attenuate the signal, and the cut-off does nothing.
Progress none the less.
W0ohoo!
One step closer to a Kosmo voice.
MS20 filter finally works.
And what lessons have we learned:
next up!
VCA/ADSR/Noise
Happy that’s work ! you’ve test it with an audio signal, maybe test it with a VCO,
you 'll had a different result.
Hey @Dud. Here is the performance through my A3340 VCO Volca Keys. There is definite quirkiness.
I had originally attempted to use a pot on the input jack to attenuate the signal for better control but for some reason the pots I tried never seemed to work quite right. I would only get sound at the very end range. I tried a 22k resistor and also got bad results. I ended up sticking a 20k trimmer and that seemed to work much better.
If the resonance pot is turned all the way to the left, I get a sweep that sounds pretty normal for a low pass filter, if I turn the res pot to the right about an 1/8 of a turn I get a noticeable blip / shelf / not sure how to describe it, when I rotate the cutoff pot. Another 1/8 turn of the resonance pot will then change the LED light from left to right side. As I continue turning the res pot to the right, the shorter the travel on the cutoff knob until the sound cuts off.
Hopefully that makes sense.
As a first attempt I’m certainly not mad at it. Though I’d love it if I could get that awesome high pitch squeal… My breadboarded circuit works really nicely and the only difference is the transistors and a 10k resistor that connect 8 from the TL074 to Pin 12 on LM13700 [I was using a PHobos schematic for my breadboard.
Has the Volca Keys installed an As3340 ???
Haha. Last minute change…
edit
for me it’s a too strong signal in, i have the same cut with a square wave and not triangle. I put a 100k attenuator pot on INPUT on all my MS20, and all works fine .
btw the 10k resistor is also in Sam’s schem.
Hey Dud,
Thanks for the suggestion.
I connected the last pot I had to my multimeter and the values were jumping around totally randomly. I think I had a busted pot. I had hit it several times with a soldering iron, soldering and desoldering resistors to get the 100k pot down to something closer to 30-50k so it must have been too much heat. Tested a fresh pot and now I have control over the attenuation.
Also instead of using my normal lm386 amp and cheapo speaker, I plugged the filter and vco into my much beefier desktop amp and speaker and the overloading issues completely disappeared. Now it’s behaving closer to what I was expecting.
So the obvious next question is:
What amp circuit should I build to ensure it can handle the modular signal?
On to the next!
I’m calling this one complete.
Well done. Amp projects can be simple or a black hole. I suggest you build a final mixer and output stage first and attenuate / buffer the s$it out of it and then most any amp will do.
Keep going and posting progress.
I have all my modular stuff into Sams Simple Mixer and from there to my Audiointerface, no Problems!
excellent.
on it 
I also had to add an attenuator on the input to my MS-20 VCF. It would do what yours is doing…but also just totally lock up and just block the signal entirely. Adding the attenuator to the input made it much more predictable. I can still overdrive it and cause it to freak out…but it happens a lot less now.
From the video I get the impression that 1: your system is overloaded by a signal amplitude that is too high and 2: the amp is not working as it should. So you are in the difficult situation that the amp will not play a signal truthfully while you are experimenting with a circuit that might or might not be working. 2 variables in 1 experiment is always problematic. I suggest you fix the amp first and then continue with the other experiments.
Glad to hear someone else having the same behavior. I added the attenuator pot on the input which help a bit. But I think my larger issue was the signal going out. I even had a simple buffer stage right before going into the speaker. I’ll build the mixer circuit suggested above tonight and see how that works out.
I’ve suspected that my amp is weird. While just testing a plain oscillator noticed as I increase the volume it will change the quality of the sound rather than just the loudness which isn’t right. I’m on the hunt for a better amp circuit. I built this one 2 months ago, so I think I can tackle something a little more complex in terms of circuit design.
i have a weird issue where it just seems that audio is fed through. The cut off does nothing and so does reasonance, it makes the leds light up but thats it. Only volume control seems to work…
(edit) the volume also seems to be all or nothing
if I’m not mistaken there is a volume control only on the cv in, how can it work if the cut off does not work ?
what stripboard did you use ?
do you have pictures of your build ?
I added volume control to the input, mine is a sorta modified version to have the same inputs as the performance filter.
When I say the cutoff doesnt work its just stuck at “max open” so there is just full fat sound all the time and twisting it seems to do nothing.
I used this layout with some more input jacks and volume pots in the way it says to.
Are your BC558 transistors the right way round?
And if you’re using different compatible transistors, have you got the CBE orientation and pinout matched up right?
Yeah they are the right way, both flat sides facing in