Building a 4-knob expression controller with a bonus pedal input and a switch to toggle between the external pedal and Knob 1. I shall call it the EX4K. #diy #guitarpedals #blackhillfx via Instagram: http://ift.tt/2kmoyBs By Philip Cain Ninja Master of the Series of Tubes, musician, audio engineer and geek. More about Philip... View all of Philip Cain's posts.