MFOS SVF Problem - Cutoff + CV no effect

So I designed this 1:1 clone of the MFOS SVF and I cannot get it to work. The cutoff pot and the CV inputs don’t do anything, the outputs all output the “same” unfiltered and pretty qiet noise.
I checked all solder points and swapped all ICs and transistors, sadly that didn’t do much.
was hoping someone has some experience with the circuit.

.gif I worked off of:

my kicad schematic

If you spot any errors please let me know. If anyone wants to check the kicad files I’ll gladly upload them/send them wherever. I got 20 pcs of the filter and would rather not dump them :grimacing:

Thanks in advance. :smile:

Only thing I can see is that your CV inputs are not connected to the opamp that generates the current for the otas

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that would be awesome but I can see that A1_5 and A2_5 are connected via the pinheaders, or am I missing something? If so please elaborate I’m not entirely sure we talk about the same thing.

thank you. Very appreciated :smiling_face::+1:

Well it’s hard to tell that they are connected on pin headers, for me A1_5 and A2_5 are different and not connected. So turn the cutoff pot and measure the output of the opamp to see if you get a voltage swing before the exponential converter

Also are gnd1 and gnd2 connected together, if not how do the inputs reference ground to the converter circuit.

I did a version of that, it’s here GitHub - holmesrichards/MFOS-SVF: Eurorack adaptation of the MFOS "Oldie But Goody" state variable filter .

It was one of my first PCB projects and I would definitely do some things differently now. I had the two PCBs in separate KiCad projects. Like you I was using global labels for the power rails — it’s much better to use KiCad’s power symbols, for better readability and to better enable use of the electrical rules checker which is valuable in locating schematic mistakes.

It would also improve readability if you used descriptive labels like “SIGNAL” and “OUTPUT” rather than “A1_1” and “A1_4”. Though eventually I figured out how these labels just connect to similarly named labels nearby.

If there’s a schematic mistake I don’t see it, then again I just got up. Have you carried out all the recommended checks here?

Check also the connectivity from the transistors to the power rails and ground.

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Thank you , I’ll read your guide and check all of the power and ground connections. It will be a few days until I get to it tho

Everything is connected via the header pins all 1s are in one PCBs and all 2s on the second one

So a bit of context would have helped on how you constructed the boards with a connector between them. Have you measured the output of the opamp from the CV inputs or the emitter of the transistor that drives to the two current sources. Could it be somthing as simple as a transistor in the wrong way around or the wrong type used. I’m home now and before I was checking on my phone, now I can see things clearer and the schematic looks OK, can’t see any reason why it wont work.

Thank you for checking I’ll try to debug it the next few days, sadly I only had like 2 hours for building and debugging today. I need to prepare a test rack to do it properly. But you (and I mean both of you) checking the schematic is reassuring and I’ll keep you posted!