Hello All:
I built an Aion Nimbus board about a year ago (Maxon OD-820). I like it, but it always has sounded a little nasally to me. Today I was playing with it again, and noticed it sounded really really good with the tone knob way up, and like most of the functional adjustment was in the top 1/3 of the pot travel.
I looked at the schematic and saw that the tone pot is supposed to be a "W" taper pot, and I believe I used a "B" taper. Is what I'm hearing just the wrong pot taper, or should I try to figure out if I screwed something else up?
Both.. Put a W in there they are very different and then look at the tone circuit and see if you messed up any of the resistors or caps..
What you are seeing with the action of the pot is what you expect from a linear pot in that kind of tone circuit. It'll do that same kind of thing on both the boost and the cut with a linear pot. a W taper pot is pretty much perfect for fixing the distribution of the action of the pot.
I've never played with an OD-820, but as a Tube Screamer offspring I wouldn't be surprised by it being mids heavy which could lead to a bit of a nasal tone with the tone pot set to a position the emphasized the mids relative to the highs.
I'd try it with the 20kW and see if that makes it work better for you. If it doesn't, then you could look for other possible problems like wrong cap or resistor values in the tone networks around IC1B and IC2B.