Quote Originally Posted by progmatist View Post
Also if any piece of equipment is plugged into a different outlet from the rest, that can create a ground loop. Inducing hum throughout the entire system.
Ideally all of the power cords should plugged into a common protection device in order to prevent damage from power line spikes caused mostly by storms which damage the lines and transformers of the power utility. If one does that the likelihood of hum is lower. The nice thing about modern equipment is that it is so efficient, including power amps. When AC was developed, it was truly the most efficient because voltage could be stepped up via transformers resulting much lower currents and losses. Today however, if everything was reworked (sorry Tesla the father of AC) it would be high voltage DC because DC can be efficiently converted to lower voltages and the most efficient equipment runs on DC. This sources of hum would be eliminated and the hazard of AC in the home.