Two new modules in one day! Well, one of them hardly counts. Still.
Back to Kosmo format. Here’s the Sallen-Key VCF from Barton Musical Circuits.
The board was designed with Eurorack in mind. It’s small, and rather densely packed. Still, no problems assembling it and it went together quickly. As designed the pots are all board mounted, on 1″ centers. Too close together for my taste, especially for Kosmo. So I moved the CV level pot from the middle position to the bottom, panel mounted. That was the only change I made. The panel is one I designed and had fabbed on FR4.
This thing does some crazy stuff with the resonance turned up past about midway. Not sure if that’s the intended behavior but I don’t really want to change it. If I want a clean and boring resonance I can use another filter. Maybe I might change a resistor to make the onset a little later, though.
Added later: I did make that change. As built with the specified values, I was getting self oscillation with the resonance pot only about halfway up. I reduced the 3.3kΩ resistor to 1k and now it self oscillates at around 3/4 maximum.
The other module, a real quickie: Three passive attenuators.
These are the first two modules for Kosmodrome.
Analog Output 
Hi Rich. My next build for my 5U modular is a BMC Sallen-Key filter using one of his PCBs. M.B. specifies 1nF polyester caps for this module. For similar designs I have seen suggestions that polystyrene or other ‘up-market’ caps may give better results. It looks like you used polyester caps, but I wondered if you had a view on this?
BTW, missing your build progress videos.
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Pretty sure I did use polyester. Then again, polypropylene is $0.48 from Digi-Key. If I were building it again and were making a Digi-Key order anyway I’d use that. And in fact I have a module with a filter in it I’m getting ready to breadboard and I’m planning to use polypropylene in it. Will it make a noticeable difference? I don’t know, but people recommend it and it won’t break my budget.
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Yes, in the grand scheme of things, the extra cost isn’t worth worrying about — not really sure why I did!!!
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