At 12.48 2011.11.21, you wrote: >> Hi Alan, >>=20 >> What is the specific situation at mains frequency that you would call a >> "ground loop"? >>=20 >> Sean > >The hum you get in a PA system when connecting multiple items=20 >together, and then breaking the ground at one point removes the hum. By the way, is this hum picked from nearby magnetic 50/60Hz fields? Because on an amp the hum caused by improper ground connection may be just power supply hum injected into the other circuits (thus load dependent), which (due to rectification) will be 100/120Hz. But I suspect that a "ground loop" may act also like a magnetic "antenna" (= a reluctor pickup), thus picking up magnetic fields leaked from nearby high tension electric company's line transformers, etc.. Effectively breaking the loop is like cutting one of the two wires of a reluctor pickup.. --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .