Ground loop

A hum caused by two or more paths to earth between connected pieces of equipment, forming a loop that picks up and carries interference.

The usual symptom is a low, steady buzz that changes when equipment is moved or another device is plugged in. It is not dangerous, but it is difficult to chase because adding a cable can complete a loop that was not there before. The proper fixes are to run one path to earth, to use a transformer-isolated connection, or to move to a single power outlet; lifting a mains earth is not a fix and can make the equipment unsafe.

Example: a guitar rig buzzing from several amps and a pedalboard plugged into different sockets often clears the moment everything shares one outlet.

Ground loop

See also