Understanding, Finding, and Eliminating Ground Loops in Audio and Video Systems
"A cable is a source of potential trouble connecting two other sources of potential trouble." This joke among electronic system engineers is worth keeping in mind. Any signal accumulates noise as it flows through the equipment and cables in a system. Once noise contaminates a signal, it's essentially impossible to remove it without altering or degrading the original signal. For this reason, no system can be quieter than its noisiest link. Noise and interference must be prevented along the entire signal path. Delivering a signal from one box to another may seem simple, but when it comes to noise, the signal interface is usually the danger zone, not the equipment's internal signal processing.
Many designers and installers of audio/video systems think of grounding and interfacing as a black art. How many times have you heard someone say that a cable is "picking up" noisepresumably from the air like a radio receiver? Or that the solution is "better" shielding? Even equipment manufacturers often don't have a clue what's really going on. The most basic rules of physics are routinely overlooked, ignored, or forgotten. College electrical engineering courses rarely even mention practical issues of grounding. As a result, myth and misinformation have become epidemic! This paper intends to replace mystery with insight and knowledge.