How to track down and avoid mains hum safely
If you have a mains hum problem then
firstly identify which piece of equipment is causing the problem.
The best way to do this is disconnect all
the equipment from the mains and also all the connecting signal
cables between the equipment. Now start introducing the equipment
piece by piece until you notice the problem. The best sequence to do
this in is power amp and speakers, mixer and then connect them
together via a signal cable. Next introduce the monitors (if you use
them) and then each piece of equipment.
Once you have identified the offending
piece of equipment then you will probably need to seek qualified
advice on solving the problem.
Never, ever remove
an earth wire from a mains plug to avoid the problem!
Most powered speaker systems and monitor
systems now have a 'ground lift' switch which avoids the problem
when connecting them to a mixer.
Many pieces of kit such as mixers and
keyboards are 'double insulated' i.e. they do not have a earth wire
connected to the mains plug - therefore mains hum can not occur.