Power Amp transformer hum - intermittent and increases and decreases in a few seconds

Try a cheater plug.

A cheater plug should only be used to help diagnosis if you have a ground loop problem.  It is not a solution as it poses a safety risk.

Agree.  I did try a cheater plug to no avail.  Thx to all for their input. It is much appreciated. 

This sounds like a mechanical vibration issue. Try this please. When the amp is on and humming lift it from the shelf so it is in you hands not touching the shelf.Is there a change? Next with it on the shelf put your hands on the amp and press on it, like hug it lol, not enough to crash things but to see if pressure on the chassis changes the sound/hum. From your descriptions it is possible the transformer has loosened or in some way is physically vibrating. What brand and model are you listening to? You say it always has had the issue. How old is it? A solution may be as easy as opening the cover and tightening whatever keeps the transformer in place. Then too is could be a defective transformer. GL

I'm using a Harman PA5800 that I recently purchased from a friend. I've had it for less than a month. The transformer is not loose, and the amp appears to be in excellent condition.  I also moved the amp to another location in my house and the amp is silent. From everything I've read on the net, I'm lead to believe it is DC Offset related. 

john_simp OP21 posts

03-12-2019 1:24pm

I’m using a Harman PA5800 that I recently purchased from a friend. I’ve had it for less than a month. The transformer is not loose, and the amp appears to be in excellent condition. I also moved the amp to another location in my house and the amp is silent.

I also moved the amp to another location in my house and the amp is silent.

Do you have a multimeter to check the voltage at the wall outlet the amp is plugged into that doesn’t buzz?
Check the voltage at the wall outlet where the amp buzzes.
Does both measure the same voltage? What is the voltage?
Does one measure higher than the other? What is the higher voltage measurement?


The wall outlet that causes the amp’s transformer to buzz. What all is on that branch circuit?
Light dimmer/s?
CFL Lights?
Florescent lighting with electronic ballast?
Cheap LED light bulbs?
Plasma TV?

Go to the electrical panel and find the 2 breakers that feed the two outlets. What breaker location (circuit) numbers are they? The numbers will tell me if they are fed from the same Line, Leg, in the panel or a different Line, Leg. (Example. Both on L1, or both on L2, Or one on L1 and the other on L2.

Is this a picture of the amp? Looks like a big toroidal transformer.
https://www.google.com/search?q=picture+of+inside+of+a++Harman+PA5800&tbm=isch&source=hp&...:
.