I was trying to dial in the Mutron effect with the H90 and my experience was similar to this. I think the starting point for me was Q-Wah set to Bass Wah mode, Q-Intensity maxed, Bottom at 0, Depth maxed (this is necessary for the effect to keep working with very high notes on the high-e string), and then sensitivity around 70-75 (whatever feels right). I only use the effect with bridge pickups, it just seems to work much better that way. Anyway, with those settings, play around a bit and focus on very low notes on the low-E string and see if they bloom too much, like with too much of a “bubbly” bass-y feeling (for lack of a better term) and increase the Bottom control in tiny increments until it sounds like you want it. I think I also ended up with mine in the 5 to 10 range.
One huge thing I figured out that I haven’t seen mentioned elsewhere is that adjusting the Input Gain for the preset can make this work far better. I noticed that the effect sounded best when I picked very softly and very staccato. Reducing the input gain by 2-3db sends less signal into the algorithm and enables you to get the effect while picking a bit more “normally” (you still need a staccato technique, but you don’t have to pick so softly). I got decent results all the way down to -5db, but found I preferred -2 or -3db after playing around a bit. This may reduce the perceived volume, so compensate for that by increasing the preset Output Gain.
I also like using this effect stacked into light overdrive, or an edge of breakup amp tone as opposed to fully clean. Might just be a personal preference thing, but I think it sounds better that way.
