A schematic diagram showing one solution to the problem of a ground loop between electronic components - break the ground shield in the signal cable connecting the components.   A ground loop is an inadvertent electrical circuit or loop created by the ground wiring of electrical equipment.  Ground loops are a major cause of hum and interference in audio, video, and computer equipment, because circulating currents induced by stray magnetic fields from nearby 50/60 Hz equipment can cause AC voltage dropped across signal grounds.  In this diagram two AC powered electronic components, C1 and C2, are connected by a shielded signal cable S.  The ground shield of S, along with the ground wire ("third wire") P in the components' power cord and the building's utility ground wiring G form a ground loop.  By breaking the shield conductor (red) between the two components, the loop is broken, preventing the ground loop current from flowing.  The shield should be broken at the "load" or "destination" end of the cable (C2) not the "source" (C1).   This solution works as long as both components are grounded to the building wiring, but if one of the components does not have a ground wire in its power cord, it will be totally ungrounded ("floating"), and AC leakage currents will result in very loud "hum" in audio signals.   Information and circuit from Larry Robinson, About Ground Loops, MidiMagic website
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