After finally finishing my “inspired by LMNC” MS-20 build and fixing a couple of PCB glitches, I was a bit puzzled that my notes said 10k for the input resistor, but my schematics had a 100k there. Trying to figure out where I got these values from, I checked some other schematics, and it seems like the stripboard layout uses a 10k resistor on the input (as does Schmitz), while the performance layout uses 100k.
These resistors form a voltage divider with a 220 ohm resistor, so for a full 10 Vpp in you end up with either 220 mVpp or 22 mVpp (ignoring the feedback loop). The former is a bit high (not that you’ll damage anything, but you’ll get plenty of distortion with the full 10 Vpp in (EDIT: and you also risk lockup, see below) unless you attenuate the signal, but then distortion isn’t necessarily bad in a gnarly filter). The latter is really low, though.
So if you’re getting a low output, it could just be that you have too much attenuation on the way in – check if you have 100k resistors there, and consider replacing them with a lower value if you do. You could just solder another 100k in parallel with the existing one to check if that improves things.
EDIT: Tested with a 100k and the output level dropped through the floor. I don’t trust my attempts to simulate/calculate, so will have to get out the scope later, and measure some measurements.