I'm currently doing some work on my Univibe pedal to resolve a hum issue whenever I try to place it in my Marshall amp's FX loop, I'm suspecting that I inadvertently set-up an earth/ground-loop when I originally installed all the circuitry in it's current housing, so, I'm going to go and re-do all the ground wiring and hopefully remove the suspected earth/ground-loop and therefore make it quieter so it's useable in a live gigging situation.