Today's tip is about those pesky guitar "voltone" controls.

"When I turn the volume control on my guitar down even just a little bit the tone gets noticeably darker. Originally I thought this was interaction with my amp, but even when it's plugged directly into a mixer I can still hear it. What's up?"

It sounds like you have passive electronics in your guitar (as most guitars do). Some of the same things that make a simple passive guitar sound great can also be an annoyance. Your pickups are coils that are wired into a circuit with resistors and pots (your volume controls) along with capacitors and pots (tone controls). The great thing about these simple passive wiring systems is there is a purity to the sound that's often not there with more complex active systems. All analog tone controls are based around the principle of different resistances in series and parallel with coils and capacitors. The problem is that in a guitar or bass all of these passive components interact with each other. Consequently the volume control in many guitars does change the tone as well. Furthermore, the type of load the guitar is plugged in to can compound this behavior. This is why some direct boxes will sound terrible on certain types of guitars and is also a contributor to one amp or another sounding better. Changing any of the controls produces interactions between all of these elements that can be magical or disastrous. It's just part of the personality of a given instrument.

Guitars with active electronics (you can identify them because they are powered by a battery) are much less prone to this type of behavior. They are also much less sensitive to the type of load they are connected to. The preference of one over the other is subjective, but many players specifically enjoy the idiosyncrasies of the old passive designs and don't like the fancy active electronics.