Ok, so sounds like that’s expected behaviour. Thanks!
I think part of the issue is that the MS20 highpass is realized by swapping signal and ground in portions of a 2-stage lowpass filter, rather than swapping the R and C components around. Assuming zero resonance to simplify (so feedback = 0 V), the lowpass path is RC→RC (2nd order, 12 dB/octave) while the highpass path is a single CR (1st order, 6 dB/octave). I should probably model/measure to confirm… or get myself an MS-20, maybe.
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Hey guys!
It’s nice to be able to be part of the lookmumnocomputer community 
So. Im building the Performance-filter myself but haven’t been able to make it work yet. Can you guys help me out by posting a picture about the front and back side of the pcb panel?
I think I must have messed up with the placement of certain parts…
<3
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i’m having an issue with this filter.
in highpass mode, when the frequency knob is above ~1/3 it starts to self-oscillate very loud at high pitch sometimes and also sometimes it introduces kind of white noise, all depending on where the resonance is set… at low resonance you just hear a click at 1/3 and then nothing above there.
seems like a grounding issue again, but i reflowed everything already… does anyone know which of the components are used in the HPF part of the filter?
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It’s the same circuit, the signal is just injected in a different location:
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ok… on the schmitzbitz website it says
“If you want to add the highpass section you have to insert the input signal at the grounded end of the 1n cap between O2 and A2”
which one of the 3 is that capacitor in sams design?
There’s actually two of them – C1 is used in high pass mode (connected to the input signal S1), and C16 in low pass mode (connected to ground).
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where did you get that schematic? on the lmnc page i could only find the link to the schmitzbitz schematic?
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Looking for a sub for C9 470nf. I have everything but that one part.
You don’t have to hit that value exactly. What values do you have available between, say, 100nF and 1uF? (film, ideally).
Ceramics aren’t ideal for this position, but as a stopgap measure you could solder in two 220 nF in parallel (that give you 440 nF which isn’t that far from 470 nF). But I’d suggest getting some film caps next time you order components.
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I can wait and make an order, thanks for the info I do appreciate it very much!
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Hey, I’ve hit a wall with this filter. I tried recreating it on a strip board and the low pass seems to be working fine, but the level of the high pass is significantly lower than the low pass. I tried debugging it, but failed. Then I tried drawing up a schematic and printing it using photoresist, but the problem still persists, any idea what might be the cause of the issue?
I’m about 90% sure it isn’t the pot, but I’ll try replacing it tomorrow. I can post pics and the schematic here tomorrow as well.
Any help would be really appreciated, been stuck on this for about a week.
Thanks in advance!
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hi, there is 2 other thread about problem with the filter
maybe here some way
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Hi! I’m also curious as to where you found that schematic. Did you make it? I’m troubleshooting my filter now and that would be an incredible help.
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Why film? I’ve heard that film is better for musical circuits but I noticed that Sam always uses ceramic. I always wondered about that and why if film is better for music then why doesn’t he use film instead?
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ceramic capacitor work but film are better
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hey! I have used ceramics purely because I have them sitting around, in audio applications I can’t say I can tell the difference (im sure there is a difference but I dunno in a synth I gotta say its reasonably negligible, but im happy to be proven wrong), the only time I have felt they are important is for some voltage reference or for instance the frequency cap in the vco. film are indeed better! but ceramics are fine.
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Understood. Thanks Sam for the explanation. Are ceramic and film equally interchangeable in musical circuits? For example, could I just swap out film for any ceramic of the same value in any board design? Thanks again!
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