[asterisk-users] Help 60Hz Hum?

[F6HQZ]

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