QTron+ (w/ boost) Issues

[anotherjim]

I was going to add some stuff.
Cable...
Good guitar cable has a conductive plastic layer on top of the centre hot signal wire insulation. It greatly reduces handling crackles. The conductive layer contacts the bare wire shield so is grounded - it can creep along until it touches the tip solder tag in the plug. The conductive layer isn't perfect zero resistance but it causes a partial short that can drop the volume. This fault can be missed by simple continuity testers so measure between tip & sleeve on a high resistance DMM range instead - it should read infinite resistance - no ifs or buts.
When assembling a plug on this cable, the conductive layer (often black) should be stripped off as far as you can revealing the hot wire insulation (often clear).
Strat...
The first place to look is under the jack plate, There could be conductive screening paint in the cavity or damaged wiring. Again, this can create only a partial short to ground causing volume loss. Often the jack nut comes loose & gets tightened up without a thought to what may have happened when it was spinning around!

[pruttelherrie]

No volume until 9 or 10 might be changed by taper of pot; a linear taper takes a long time to get to that useful range, the audio sweeps up there faster.

You raise a lot of good points but I do believe you have these backwards.

[idy]

My bad!