Line6 M5 “Expression Knob” Mod

CAVEAT: If you do this mod you can’t use a Line6 -style expression pedal via the jack any longer (well, you can, but you only get half the “travel” between minimum and maximum – you never get all the way to your maximum).

EDIT. Jack at JHV3 says:

The stock switches share the same reference to ground, so you need just one (orange wire) to your momentary switch.

The expression pedal jack on these is “switched” so when a plug is inserted it tells the UI controller to look for it. Take advantage of this by moving your gray wire to the “switched” Tip connection, then whenever you do use an external pedal it will remove the modded pot from the circuit and give you full range with a treadle.

The mod is reversible (by disconnecting wires from the PCB, though you’ll still have the knob mounted).

This one is a really easy mod; it’s much easier than the previous dedicated scene select mod.  The Line6 M-series are all capable of using an expression pedal to change parameters within a given model. Things like delay rate, mix level, tones, pretty much any parameter can be adjusted on the fly using Line6’s expression pedal or any expression pedal that uses a 10k linear potentiometer (so, Ernie Ball VP, VP Jr.  are out, as are standard Mission Engineering pedals.) The Line 6 expression pedal is quite simple, using only a 10k potentiometer between the tip and sleeve of a regular 1/4″ connector. When the potentiometer is all the way “up” then you can set the maximum parameter value, when it’s all the way “down” you can set the minimum value. This video shows you how to set these (and happens to use a knob as well).

In my case, I once made two expression pedals out of old wah shells and 10k pots. I used these with an M13 for about a year. In a recent attempt to scale back my rig while maintaining functionality, I now use two M5s, and modded them with the dedicated scene select as mentioned earlier. But, I also want to be able to take advantage of the expression pedal possibilities but don’t have room on my board for either the two wah-style pedals nor the expression switch/double preset mod which uses a fixed 10k resistor with  a DPDT between tip and sleeve.

So I decided to mount a foot controllable knob to  the top of each unit. As usual, this could be done to the M9 and M13 and probably any other Line6 unit that takes an expression pedal.


Here’s what you need (for one pedal):

1 – 10k 9mm PC-mount mini pot, Smallbear. It’s not possible to use standard size 24mm or 16mm pots for this job.
1 – Large MXR style fluted knob, Smallbear.
1 – Knob Cover, Dunlop ECB131, Smallbear.
Hook up wire

1) Take the bottom off the M5, which is a bit tricky. After removing the four screws on the bottom and the MIDI port screw, you need to push from the side opposite the MIDI ports, this will dislodge the bottom panel so that it can be easily pried up and removed.

2) Remove all the nuts from the jacks. This will allow you to remove the main PCB. Make sure to disconnect the ribbon connector that connects this board to the upper board. Mine had hot glue holding it together. This was easily dealt with by using a utility knife to slice the glue near the connector joint.

3) Remove the knobs from the topside of the unit using a slot head screwdriver to gently pry them up. Unscrew all the silver screws with lockwashers that connect the second PCB to the standoffs inside the unit. Disconnect the quickconnect that connects this board to the footswitch board.

4) The new pot can positioned in line with the footswitch, on the top plane of the pedal directly under the Line6 branding. I used masking tape to mark the position using the knob cover for guidance, like this:


5) Putting the unit aside, wire up the pot like this (the yellow wire is the tip, the grey is the sleeve:


6) Mount the pot inside the unit (you can see there’s plenty of room even with the double preset switch in there:


7) Now you reassemble the unit but before putting the main circuit board into place, solder the yellow and grey wires to the correct spots on the PCB:


…and use hot glue for redundancy.


8) Now you can reassemble. I did it like this, but there’s lots of room to route the wires differently:


9) The mod in its final stages of completion:




It’s actually quite easy to move, and you can approach it with your foot from a variety of directions. It doesn’t interfere with any of the footswitches either!

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