I'm with Greg on this one. Your amp should have a nice power supply that would include DC voltage regulators after the transformer and rectifier. The regulators, along with the filter caps, should give you plenty of stabilization within the AC voltage swings you are seeing.
LarryC mentioned that you should tighten your connections at the service and throughout the panel to try and alleviate the issues with your power service, and I agree. This is the first step in diagnosing a voltage fluctuation, as it is cheap and very common cause of the issues you are describing.
If the problem persists with the voltage swing, I would contact your PoCo. They may have a loose connection at their transformer as well. At the very least, they can put a data logger on the circuit and see if the problem is on their end.
Good Luck!!
