What's the difference between a volume pedal and an expression pedal?
A volume pedal expects an audio signal (like an electric guitar) to be passed through it. An expression pedal does not pass a signal through it. There are a few pedals that are "combination" Vol & EP.
Here's a very simple volume pedal circuit (
courtesy of Ernie Ball):
An expression pedal is even simpler. It just connects the terminals of a potentiometer ("pot") through a cable to a tip-ring-sleeve ("TRS") plug. The center (middle) terminal on a pot is usually the "wiper". This is the portion of the pot that moves, when you twist the knob. Some expression pedals are wired "wiper to tip," while others are wired "wiper to ring." Here's a diagram showing one way the EP pot can be wired to the TRS plug:
Pots used for these applications typically have two key values:
Resistance (ohms) and
taper. Common resistance values include
250K ohms,
500K ohms for passive volume pedals. Taper values are usually either
linear or
logarithmic ("audio").
Can I use my volume pedal as an expression pedal?
Maybe so, but probably not. It depends on (a) the resistance of the pot, (b) how the pot is wired (wiper to tip or ring) and (c) whether you can adapt your volume pedal to a TRS plug. You might try a
stereo-to-mono adapter "Y" cable (also known as an "insert cable"). Insert one of the mono 1/4" plugs into the Input jack of your volume pedal, and the other mono 1/4" plug into the Output jack. Then, use a
TRS patch cable to connect the Y-cable rig to the Expression Pedal jack on the device you want to control. If the pedal "sweep" doesn't seem right, try swapping the Input and Output plugs -- this changes the wiper-to-tip (or wiper-to-ring) orientation of the pot. If you still don't like the results, go buy an expression pedal.
