My friend is experiencing humming + beeping noise in his class A amplifiers when the heat pump (air conditioner) is plugged in. And the intensity increases when the pump runs. He is neighbour to a factory / industrial building, so there is alway a slight beeping sound in the amp even on zero volume.
He has 3 amplifiers, and would like me to design a filter (250V, 16A max and 4 outlets - encapsulated).
I successfully made a filter many years ago, to stop my TV from blinking when I turned on the relay controlled lights (Nexa wireless). But that was only 3A.
What's the typical noise here and what is the best approach? Is it a surge protector, a DC block, EMI filter, etc?
He only needs 4A on each outlet, so maybe put a 4A (plus margin of course) filter on each outlet (fused), instead of one 16A filter on the input?
I am designing, not buying off-the-shelf. Anyone with suggestions for designs/schematics/etc or critical parts (e.g. chokes)?