Colin Wonfor’s Clinic: Amplifier buzz even when power switch is off!

Colin Wonfor

Dear Colin, I need some theories and hopefully answers please. This is a situation, neither I, not anyone who I asked, have encountered before. It is very simple and puzzling at the same time. Here it is:

There is a faint buzz coming from the amplifiers, NOT the speakers, barely audible from a few feet away. I can also hear it with the ear on the transformer cover; it sounds like a slight mechanical vibration.

The strangest thing is – you can only hear it with the amps and the whole system OFF, cold. If the system is playing for some time, and then turned off – there is no buzz. Also, only when the system been off overnight.

I've disconnected the power cord from the amps – silent (obviously). Again, only happens with the amps OFF and the power cord connected to the wall. I'm not naming the brand on purpose, because I think it's completely irrelevant in this instance. Please, throw in your theories and assumptions. Thanks in advance.

Its sound like the power OFF switch may only remove the power to the amp electronics and not the transformer, and under no load some do buzz. Now when the transformer is warm the iron core which is made from a thin sheet of magnetic steel expands and the mechanical buzz stops. Thank you for the question.

Colin