The Humdinger was designed to eliminate earth loops in audio equipment by isolating the second output. Earth loops are a common complaint. As soon as the ground on your gear has more than one main route to earth, you have the potential for an earth loop. The best and safest way to get rid of an earth loop is to isolate the ground that is causing the hum.
Using the HumDinger to get rid of earth loops is easy. If you use 2 amps all you need to do is stick the HumDinger at the end of your effects chain. Your main (buffered) output goes to one amp and the isolated output goes to the other. Your earth is consistent through the main output but isolated through the isolated output.
Using a mains powered effects pedal, simply place the HumDinger in the chain after the mains powered effect. The Mains powered effect is your main ground and the ground from the amp is isolated.
WHAT THEY SAY
It keeps your signal levels, impedance and tone intact, even when driving long cables and using a large pedalboard filled with true bypass pedals, lets you flip the phase if you need to compensate for one amp being out of phase relative to the other, and it does it all at a reasonable price. If you're running a stereo or dual amp setup, is definitely a must-have. It will kill what ails your tone.
Phil O'Keefe - Expert Reviewer