How They Work
So, what’s happening under an expression pedal’s hood? Glad you asked. The circuit within a pedal’s expression jack reads a voltage, from 0 volts to 5 volts, and adjusts one of its sonic parameters accordingly. The most basic expression pedals don’t have or need power, because the voltage comes from the effects devices they’re plugged into. An expression pedal’s foot control simply divides that voltage, resulting in more or less voltage.

A volume pedal can be hacked and converted to an expression pedal. The easiest method is to use a standard volume pedal and buy a Y cable that has a stereo 1/4" plug on one end (called a TRS, for tip/ring/sleeve) and splits into two mono 1/4" plugs at the other. Plug the TRS end into a pedal’s “EXP” input, the “ring” plug of the Y cable into the input of the volume pedal, and the “tip” end into the volume pedal output, and you’ve got it (see diagram).

This illustration shows the simplicity of the common volume pedal with Y connector hack, with the stereo end plugged into the effect and the tip and ring lines going to the output and input jacks of the volume pedal.
Illustration by Dan Formosa

Here’s another trick using a basic volume pedal: Take a Y connector that splits a stereo 1/4" plug into two female stereo jacks—the type used to plug two headphones into a single output jack—and use it in conjunction with the Y cable hack described above. This setup doubles your capacity to split the signal and thus lets you control multiple effects at once.

To operate two effects units simultaneously, Vernon Reid does something similar using a Boss FV-50 Stereo Volume Pedal that essentially functions like two volume pedals with a single foot control.

These hacks may require modifying the volume pedals a bit. The values of the potentiometers in the hacked pedals would need to be changed to 10k ohms or 25k ohms, and you may find other limitations in their operation—but they will work.

For further information on how expression pedals work, Mission Engineering’s Paul Shedden and “Basic Concepts—Expression Pedals.”

Do I Want One?
While expression pedals can be used to conjure some extremely dramatic effects, they can also be employed with subtlety. You can gracefully ease in and out of echo, for example, or add reverb only when needed. Given the control an expression pedal allows, you might even be able to downsize your pedalboard. Who can argue with coaxing more sounds from fewer devices? If you already have an effects unit with an expression pedal jack, you owe it to yourself to at least borrow a foot controller and plug in to explore the possibilities. There’s nothing to lose and potentially much to gain. Or, as guitar tech Sheppard suggests, “They are not for everyone, but if you are constantly bending over to adjust the dials on your effects pedals, you may be a great candidate.”

Getting into multi-effects processing via expression pedals has a variety of entry points, from do-it-all devices like the Kemper Profiler to Zoom’s G1Xon multi-effects stompbox with a built-in foot controller.

Controlling Multi-effectors and Amp Emulators

If you’re willing to take a deep dive into advanced signal processors and amp emulators, you’ll have the ability to assign an expression pedal to any number of effects within their capabilities. Expression pedals can be assigned to control wah, pitch shifting, tremolo, reverb, rotary spin, delay, overdrive, compression, distortion, fuzz, chorus, flanger, phaser, harmonizer, and other effects. You can also control the curves at which those effects operate, and assign an expression pedal to control multiple effects at once. It will take a quick—or maybe lengthy, depending on the device—study of a unit’s manual to understand how it will work best with an expression pedal, but the possibilities are typically vast.

Some of the more fully capable units include the Kemper Profiler Head and Profiler Remote ($2,268 street), the Line 6 Helix ($1,399 street), and the Fractal Audio Axe-Fx II XL+ Preamp/FX Processor ($2,249). But there are options for lower budgets, such as the Zoom G1Xon ($69 street), a multi-effector with a built-in expression pedal. And there are countless expression-ready, single-effect stompboxes, such as the Boss RV-6 Digital Reverb ($149 street). Happy hunting.