DIY Expression pedal
 

Can these be made easily? Boss say that using the wrong type can result in the end of civilisation.

A volume pedal consists of a pot mounted in a pedal housing that can turn the pot. The pot is then wired to a couple jacks. Nothing simpler. You can run it in the effects loop or in fromt of the amp. I can't imagine how it could ever hurt anything.

You can probably find a used Ernie Ball or even an old SHo-Bud for reasonable money.

I know some folks at diystompboxes.com suggested finding old sewing machine pedals at garage sales or auctions as a housing.