Here’s a quick video of a 2 in 1 Volume and Expression pedal. Like a wah it has a footswitch built in that lets you switch between volume mode and expression mode without switching cables. I modified a bespeco weeper wah to build this which is a switchable volume/wah.
– It had a dual pot which meant I only needed a 3PDT switch, but I had a 4PDT, so I could add an LED in the future.
– If you only have a single pot, you need a 4PDT to do the switching.
– Mine is a buffered volume pedal, with true bypass switching, in case something fails I can bypass everything.
– You could easily modify it to be buffered bypass so that tone stays consistent between switching
– If you had a 500K pot you could probably get away with no buffer, although in expression mode it would then be 500K, and most expression inputs specify for 10K to 100K. It should work, but might not work in every circumstance.
I haven’t had time to do a schematic, so the pictures will have to do: