From Ernie Ball:

The Ernie Ball Most Valuable Pedal provides a super smooth foot sweep, ideal for precise volume control with no high-frequency loss at any volume. Designed to maximize versatility, this pedal works with both active and passive electronics and is equipped with a minimum volume knob as well as a powerful gain boost, allowing players to increase the audio signal up to +20 decibels. And of course, as you've come to expect, the Ernie Ball MVP boasts a compact, rugged design, consisting of aircraft grade aluminum housing that is virtually indestructible. Requires DC 9V/100mA minimum power supply or 9V battery.