Ebtech HE8 Hum Eliminator
Almost all AC hum (60Hz in the US) is caused by groundloops. Rather than filtering, the HUM ELIMINATOR prevents groundloops from forming in the first place. Just plug the HUM ELIMINATOR into the signal lines between offending pieces of equipment and you're done. It's that simple, quick and easy. The HUM ELIMINATOR does more than just stop your sound systems from picking up AC hum. It's also one of the most cost-effective ways to convert unbalanced signals to true balanced signals.
The HUM ELIMINATOR prevents ground loop antennae from forming and picking up AC hum. AC hum & noise is almost always caused by a loop antenna effect across signal lines between two or more pieces of gear, or by long unbalanced cables picking up noise. Loop antennae are basically a type of radio antenna, which tend to pick up the 60Hz (and harmonics) AC signal being broadcast by a building's electrical current. These loop antennae are closed circuits usually along the ground wires and hence are commonly called ground loops.
Unbalanced signals are more susceptible to picking up electrical noise & RF interference than balanced signals. The longer the unbalanced cable, the greater the chance of a problem.