Moog Ladder VCF

Voltage-controlled filter (4HP)

Inspired by:
Transistor Ladder Filter by Kassutronics (among others).

interactive version

Probably the most widespread synth VCF, this design has been implemented by many, many, many different people. I settled on something very similar to Kassutronics' version.

True to the original, this doesn't have the resonance gain compensation seen in some other versions (notably the one by HaraldsWerk).

Build notes

Take care when installing the trimmers and potentiometers, some of them are squeezed a bit too close to each other than is comfortable.

The 47 nF ladder capacitors have a 0805 footprint, but are highly recommended as class 1 dielectric. This is the largest class 1 value I've been able to find in this footprint, so it is possible (squeezing 1206 components onto the pads may also work).

Not present in the first PCB but useful to have is a trimpot that sets the resonance feedback, in my first build this was not as strong as it could be. Can be tweaked by kludging the topmost 470 ohms resistor under the Resonance potentiometer, next to the 220 uF elco.