Yes, Jay and Philip, you are right, but you can also have hums if ground cables for chassis protection against electrical hazards are making loops, if certain of them are in parallel and if they have different length between the equipments to protect. Many audio stages (unbalanced side, not balanced line side) are sensitive to that case. You can also encounter this case with PCB ground design.
You can also have hums (often harmonics) due to a poor filtering from the power supplies (too old or poor quality chimical capacitors). And also, in rare specific cases, due to a strong radio field, near high power transmitters. It's not so easy to found what is the exact cause. Use an oscilloscope to check the different signals (audio, power lines, earth cable, etc...). Best Regards, Francois BERGERET France _______________________________________________ --Bandwidth and Colocation Provided by http://www.api-digital.com-- asterisk-users mailing list To UNSUBSCRIBE or update options visit: http://lists.digium.com/mailman/listinfo/asterisk-users
