First build Line 6 EX 1 expression pedal clone

First build Line 6 EX 1 expression pedal clone

Building a solid expression pedal for my M9 was the first project I undertook. I scoured the internet looking for information on how expression pedals function and the various standards (Ill come on to this a little later). I got all the info I needed to feel confident to do this. It seemed the Line 6 pedal was a pretty simplistic design so what better place to start than with an easy build like this?

I wanted a metal enclosure to stand up well to being jumped on so that was the main consideration for the pedals housing. After plenty of looking about I decided that a wah wah would be the best option. I found a couple of Ashton Wah pedals on eBay going cheap so snapped them up. Cosmetically theyd taken a bit of a shoeing but thats nothing some spray paint couldnt fix if needed. Theyd need to be gutted completely, but the treadle mechanism kept.

My shopping list for the expression pedal included surprisingly few parts:
1 x enclosed stereo jack (you actually only need a mono jack of any kind)
1 x 47k resistor
1 x 20k linear (marked type B) pot
A few lengths of 22 gauge wire and some heatshrink tubing
An expression pedal enclosure (an old wah in this case)

Then Id need access to the usual workshop tools (screwdrivers, wrenches, socket set, spanners) including soldering iron.

Ok so whats the basic prinicple behind an expression pedal?  "The way almost every expression pedal out there works is that it takes a reference voltage from the device it’s connected to, divides that voltage down by a certain amount and then feeds it back to the device." (Strymon blog)


As I mentioned at the start, there are a couple of protocols for expression pedal design. Probably the most popular involves a TRS cable design. TRS basically means youll need a stereo cable (TRS standing for Tip, Ring and Sleeve). "In electronic terms the reference voltage is on the “ring,” the control voltage is fed back to the device on the “tip” and the “sleeve” is ground." (Strymon blog)

The Line 6 unit differs from this approach in that it employs a resistor to divide voltage and sends this voltage back through a standard mono guitar cable.

I believe the M9 unit is looking for a resistance of around 13k ohms in order for an expression pedal to interact with its controllers effectively (in fact I understand the M9 is happy to take a broader range - probably from about 9k ohms up to 20k ohms, though dont quote me on that! Im sure a simple 10k ohm pot in an expression pedal will happily drive the M9). Ok so how do we get to the target 13k ohm range? Using an online parallel resistor calculator like this one will let you know what values you need to stack together to get the desired result. The way I have achieved this is to put a 47k ohm resistor in parallel with a 20k ohm treadle pot: this gives you about 14k ohms - as near as damnit to the required 13k ohm target.

I took the beaten up wah enclosure and sprayed it with automotive primer, then a couple of top coats of automotive red, finished with a lacquer to harden the paint off. I used the old treadle mechanism to house a small 16mm Alpha pot. There was already a grounding point on the pedal (the screw in the housing to which the black wire goes). I simply had to wire up the pot, the jack and add the resistor (with heat shrink on its legs for a little protection from shorting out). I bought a pack of skateboarders grip tape to stick on the top to give nice underfoot grip.

As my first job from a few years ago I was really proud! Looking back I can see how the soldering was a bit sloppy, buy hey, youre not going to see the guts so who cares? It works and is solid. Thats good enough for me!

Hand drawn schem, thanks to Harvey for the loan of his Crayons:

First build Line 6 EX 1 expression pedal clone