I went into the electronics, and reversed the leads on the volume control for a nicer 'sweep'. Then I started troubleshooting a problem with the passive tone control that turned out to be an interaction with the EXP circuit. Long story short, the EXP disables any tone control that is downstream from it. I moved the tone control upstream, and now it works fine. I have a separate review for the EXP tone control, I'm not all that impressed, but I'd say try it yourself, it's not expensive or difficult to install.