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

don_c55826 posts

03-11-2019 4:16pm

My Pass Labs XA60.5 never buzzes and it has Toroids.

Just a guess because Pass Labs incorporates a DC blocker in their power amps.



Bryston does......
https://www.diyaudio.com/forums/power-supplies/161428-variations-dc-main-filter-buzzing-toroid-trans...




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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&...:
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john_simp OP22 posts

03-13-2019 2:17pm

I don’t have a multimeter. This is my basement Home Theater and I do have cheap LED light bulbs in use. I turned them off to see if I still get the hum. I’ll check it over the next few days to see what happens. Yes, that’s the picture of the amp.

You can pick up a descent Fluke multimeter at HD for $50.00.

I would suggest you turn off the breaker that feeds the wall outlet that feeds your HT system and see what all is on the same circuit.

The circuit could also be part of a 3 wire multiwire branch circuit. (The device causing the DC offset could be on the other circuit and traveling on the common, shared, neutral to the outlet that feeds your HT outlet. Nothing more than just a guess though.)

Your situation can be solved by having a new 20 amp dedicated branch circuit installed. You already have discovered the amp doesn’t hum/buzz if plugged into an outlet in another room.

Cost? Depends on the distance from the electrical panel to the new outlet, and the wiring method needed/used because of the basement wall and ceiling finishes. Example, is the ceiling drywall? Is the wall the outlet will be on wood stud with drywall?

Usually electrical wiring estimates are free. YMMV though where you live.
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