Today a friend asked me a question about using an passive volume pedal with an active pickup. I had to admit that I had no idea what that would do. So, I learned a bit today and thought it would be good to pass along my newly found knowledge.
To break it down simply, passive volume pedals do not require power. They are essentially the same thing as a volume knob on a guitar. They work well with passive electronic systems on guitars like single coil pickups and humbuckers which do not require power. However, using them with an active pickup, such as a battery operated pickup on an acoustic/electric guitar will cause a loss of tone and possibly inaccurate volume.
An active pedal is a pedal that has a small amplifier in it, thus requiring a power source. Active pedals are perhaps the most common pedals found. These will work well in any circumstance, but are especially needed in an active electronic situation such as a powered pickup on a guitar.
Now, in the case of the Ernie Ball VP pedals that we sell here at Five-Way Switch Music, technically both of these pedals could fall under the realm of passive pedals (neither requires power). However, in technical speak, the potentiometer (an instrument for measuring an electromotive force by balancing it against the potential difference produced by passing a known current through a known variable resistance.) is the difference between these two. With the passive using a higher value pot of 250k ohm resistance and the active using a lower value of 25k.