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crazeydazey
Joined: Feb 15, 2007
Posts: 303
Location: England
Audio files: 4
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 Posted: Tue Mar 03, 2020 1:52 am Post subject:
MS20 VCF Maybe??? |
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Hi me again 
I seem to have a reoccuring theme here where I build something and it works but something doesn't seem quite right (Hence my Rene Schmitz 4069 VCO and my yusynth ADSR in other posts around here)
I finished my LMNC version of the MS20 VCF last night (late last night) and gave it a very quick test to see if it worked , it did, squealed like a pig she did, happy days.
BUT me being the squealy squelchy acid lover I am I wanted to hear that baby self oscillate like there is no tomorrow.
So I crank the res up full and started slowly turning up the cut off freq knob.. and ooooooh there she is.. a bit more ..hmmm nice, more .. nope gone ???
so the freq knob sounds like it's ok and doing what it should but I would expect it to self oscillate much further round the dial and not stop again till I turned it down??
It could just be me, it was late, I couldn't be bothered to look at it better could be nothing but just wanted to chuck this out early in case someone says "ahh yes I know what that is, mine did that.. double check R5" or something similar..
btw if you have no idea what I'm talking about by LMNC MS20 VCF... here it is ... https://www.lookmumnocomputer.com/projects#/simple-filter
cheers all
daz
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crazeydazey
Joined: Feb 15, 2007
Posts: 303
Location: England
Audio files: 4
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| Posted: Tue Mar 03, 2020 2:02 pm Post subject:
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It's cool, I've had a good play around with it today and it wasn't working properly, the problem was something I asked about in another post...
I was struggling to get hold of the 470nf ceramic capacitor and I asked if I was ok to use a MLCC (multi layer ceramic capacitor) I even emailed Sam (the man himself look mum no computer) and it looked like it should have been ok.. unfortunately it wasn't.. it doesn't seem to work with that cap.
He mentioned on his site that you can get away without that cap anyway so I removed it and just replaced with a wire and it sounded amazing .. absolutely love it , it's a beast 
I do still have 1 question though. The input signal seems to need to be quite high, if it's quiet then it seems to act like a noise gate and just cuts off.. is that normal ??
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cslammy
Joined: Apr 27, 2018
Posts: 206
Location: USA
Audio files: 1
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| Posted: Wed Oct 13, 2021 10:47 am Post subject:
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| crazeydazey wrote: |
I do still have 1 question though. The input signal seems to need to be quite high, if it's quiet then it seems to act like a noise gate and just cuts off.. is that normal ?? |
Davey: I don't know about LMNC's MS20, but I have built a couple of MS20;s based on Rene Schmitz design and it does not have special level requirements I've seen so far.
https://audiodiwhy.blogspot.com/2019/02/korg-ms20-filter-why-in-audiodiwhy.html
LMNC does not provide a schematic for his design I can find so it's hard to say what might be going on, and I'm assuming no mistakes were made in your fab, but based on rene's design-- https://www.schmitzbits.de/ms20.html -- the resistors at audio "IN" (10K, 220ohm) will set level of audio input feeding the filter.
it is very likely LMNC has something similar. You could add a voltage divider in front of the input if he doesn't.....
Different synthesizers work at different peak to peak audio levels, so those equivalent values, assuming they are in LMNC's design, could be tweaked to make the filter work better with your setup,
If your filter is now too soft, you can crank its output back up by tweaking the values of resistors surrounding the buffering IC at output. for instance, the 10K above A2 in rene's design, again, I don't know how LMNC is doing this, but it's probably similar.
You will have to experiment.
I hope this helps.
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