Ghosthouse -- thanks for the clarification. You've gotten some good suggestions to pursue. I'll just add a couple of thoughts:
1)If the problem is caused by magnetic field induction, I doubt that it would be induction into the speaker cables, due to the low impedances which are present there (especially the amp output impedance, as well as the speaker load impedance).
It could, however, conceivably be magnetic field interaction directly into internal amp circuit points. It's probably worth trying to move the amp, even though it appears that nothing had changed in the house when the problem arose.
2) While you are pursuing Newbee's good suggestion, keep in mind that a very common cause of hum, assuming your interconnects are unbalanced rca's, results from the fact that the shields of those interconnects serve two functions. They serve as the return path for signal currents flowing between the connected components, and they also tie together the chassis of the connected components, which in turn are connected to ac safety ground (if the components have 3-prong plugs). AC safety ground, in turn, is connected to ac neutral back at the service panel in the house. What that all means is that if the ac safety ground potentials (voltages) to the two components are slightly different, unwanted currents will flow through the interconnect shields as a result (at the 60 Hz power line frequency and its harmonics), which the destination component will have no way of distinguishing from desired signal, thus resulting in hum.
The ways of minimizing that effect, if it is the cause of the problem, are to use interconnects with the lowest possible shield resistance (meaning they should be both short and high quality), and by keeping the safety grounds as common as possible (meaning don't have the power plugs isolated from each other by the power conditioner or by being plugged into ac outlets that are separated by significant wiring). You could also try isolating all of the safety grounds (other than the one for the amp, which should remain connected for safety purposes) using cheater plugs, or 3-prong to 2-prong adapters with the safety ground connection not connected.
There are advantages, as you realize, to having some degree of isolation between the ac to the amp and the ac to low-level components, and between digital and analog components, but that trades off against this increased possibility of hum. Trial-and-error is commonly the only way to optimize this trade-off.
Hope that helps,
-- Al
1)If the problem is caused by magnetic field induction, I doubt that it would be induction into the speaker cables, due to the low impedances which are present there (especially the amp output impedance, as well as the speaker load impedance).
It could, however, conceivably be magnetic field interaction directly into internal amp circuit points. It's probably worth trying to move the amp, even though it appears that nothing had changed in the house when the problem arose.
2) While you are pursuing Newbee's good suggestion, keep in mind that a very common cause of hum, assuming your interconnects are unbalanced rca's, results from the fact that the shields of those interconnects serve two functions. They serve as the return path for signal currents flowing between the connected components, and they also tie together the chassis of the connected components, which in turn are connected to ac safety ground (if the components have 3-prong plugs). AC safety ground, in turn, is connected to ac neutral back at the service panel in the house. What that all means is that if the ac safety ground potentials (voltages) to the two components are slightly different, unwanted currents will flow through the interconnect shields as a result (at the 60 Hz power line frequency and its harmonics), which the destination component will have no way of distinguishing from desired signal, thus resulting in hum.
The ways of minimizing that effect, if it is the cause of the problem, are to use interconnects with the lowest possible shield resistance (meaning they should be both short and high quality), and by keeping the safety grounds as common as possible (meaning don't have the power plugs isolated from each other by the power conditioner or by being plugged into ac outlets that are separated by significant wiring). You could also try isolating all of the safety grounds (other than the one for the amp, which should remain connected for safety purposes) using cheater plugs, or 3-prong to 2-prong adapters with the safety ground connection not connected.
There are advantages, as you realize, to having some degree of isolation between the ac to the amp and the ac to low-level components, and between digital and analog components, but that trades off against this increased possibility of hum. Trial-and-error is commonly the only way to optimize this trade-off.
Hope that helps,
-- Al