LP

Eurorack Sallen-Key Resonant Low-Pass Filter

The first filter circuit I ever built, and a testimony to the radness coefficient of an op-amp and a bunch of resistors and capacitors. This isn't a voltage-controlled monster, rather a simple Sallen-Key LPF with values tweaked so that it resonates - it doesn't resonate quite as much as I'd like but it still adds a nice edge to sawtooth and square waveforms, and works really well to knock some of the 'click' out of Twin-T drum circuits.

Even so, a bunch of lessons were learnt which have been carried over to the PCB-ised version.

It has two cutoff control pots, largely because I didn't have any dual gang pots in stock at the time and I'm the impatient sort. There's quite a bit of tweakability as a result - a bit of crafty rewiring (and a new panel) and the twin pots could be replaced with a single dual-gang pot.

Power connector is the standard 16-pin (2x8) Eurorack connector - panel is made from 3mm birch ply and is approximately 6HP (30mm) wide. If you don't like it, or want to make something tidy, then you can unscrew the jacks and LED bezels and fit your own panel. Mounting is taken care of by a pair of Ettinger right-angle brackets.

Depending on how your rack is set up, you may need to take a file to the mounting holes (if you're using rails with sliding bolts then you're set) - for best results, use M3x10 machine screws for mounting; for most rails, M3x8 are marginally too short to hold the panel in place securely.

NOTE: this module uses 60/40 lead/tin solder - please wash your hands after handling it.

https://www.etsy.com/au/shop/YoMoCircuits?ref=l2-shopheader-name