Expro Expression Pedal

Expro is an expression pedal with adjustable friction, specially suited for use with guitar modelers such as Fractal Audio, Line6 Helix, Kemper and so on.

Dimensions and travel are very similar to Fractal Audio EV-2 expression pedal. The travel is linear from the beginning to the end since it uses a spur gear.

DISCLAIMER

Use this informations at your own risk, I am not responsible for any damage to you or your equipment.

Version history

• 2022/02/16 - Version 1.2 - First public release

Bill of materials

Electronics

• 1 linear potentiometer usually between 10k and 100k depending on the device you are going to use
• 1 TRS female jack

Hardware

• 1 8x65 cylindrical pin
• 6 brass M3 inserts
• 2 brass M4 inserts
• 2 brass M5 inserts
• 4 M3x10 countersunk head
• several M3 DIN912 bolts, i suggest you to buy a kit 
• 2 M3 nuts
• 2 M5x16 hexagonal bolt
• 2 M4x25 DIN912 bolt
• 6 M3x5 self threading bolt

Printing suggestions

For better reliability, I recommend using at least PETG, but this is up to you. Just print the rubbers in TPU or other flex material.

You can use 0.4 or 0.6 nozzle, every part is designed to be printed without supports.

You can choose between 4 (A, B, C, D) pot gears depending on your pot shaft, please be aware that I haven't tested them all so it may require some modifications.

Parts summary

Body

Functional parts

Rubbers

Important

The pivot must be united with the pedal and must rotate only relatively to the "friction adjuster" part. To obtain this, the steel pivot must fit tightly with the “pivot housing”. Even better is to create a flat 5mm side on one pivot using a grinder.

If you go with this solution, print one “Pivot housing - round” and one “Pivot housing - slotted”. Otherwise go with two “Pivot housing - round”. These two parts can be exchanged left/right as you prefer since they are symmetrical.

Assembling

Assembling all parts should be straight forward, here are some picture for better comprehension

Pedal assembly

Base assembly

Fully assembled

Wiring

You will need to solder 3 wires from the pot to the jack. Usually, the wiper of the pot should be wired to the tip or the ring of the TRS jack, depending on the polarity of the device you are connecting to.