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

Jea48:  thx for ideas. I'll look into them. 

Ken:  yes, very frustrating. Hum is just coming from transformer. 

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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I'm having a similar problem John, so frustrating. See my post (link below). The Emotiva didn't help my amp. Back to the drawing boards. Think I'll see if i can try out a line conditioner at a local dealer. I don't want to drop a few grand on a fancy power conditioner just to find out that it's just like the Emotiva. Fortunately, the Emotiva has a fantastic return policy!

One question for your situation - any hum/buzz coming out of the speakers or just the amp? Mine's just the amp - speakers remain silent.

Good luck.

Ken

https://forum.audiogon.com/discussions/help-i-ve-got-the-dreaded-transformer-growl

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.

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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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. 

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

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

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.

Try a cheater plug.

Mechanical hum is not always the result of DC offset. I have some DC offset on my mains and even two DC blockers in series couldn’t eliminate an obnoxious hum in one of my amps.

Anyhow, I own the CMX-2 but found the Audio By Van Alstine Humdinger works far better. I had a bucking transformer that still hummed loud when plugged into the CMX, but it ceased completely with the Humdinger.

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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Some {not all} toroidal transformers can buzz when DC is present on the power line.

My Son of Ampzilla 2000 has a faint buzz when my Canon printer turns on, and when my Keurig brews a cup of coffee.

Otherwise it is dead silent.

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

FYI, One of my many power amps, a Smart Theater Systems TA 242 ( which is actually a beefed up Hafler 220 by design, and very musical ), experiences the transformer hum ( toroidal, chassis only ), when I use my OTR microwave. Have not tried a cheater plug during these times, as it is always in rotation with others. Enjoy ! MrD.

You are very welcome! That's what this site is for. Lot's of great people on here! I've been helped many times in the past and am grateful for that and for the chance to help others if I can. 

Tom

Thx Tom!

My problem was hum with dryer/dishwasher/blow dryer/fluorescent lights/dimmer switches being used, and that's with a dedicated line to the listening room. The above posters have already given you all the information you need. Hope you get it resolved soon.

Tom

I think it's dc getting into my line too. Very frustrating. 

I had that problem once when I lived in a place with very poor power. It was DC getting into the line. I ended up just unplugging stuff when it happened and returning a hour or so later. It was annoying and aggravating. I tried gear to block it unsuccessfully. I was running a tube amp at the time.

Thx lowrider.  Amp is SS and hums only thru transformer. Hum goes up in volume and then down in a cyclical type pattern.  

Thx E. I'll try the breaker solution after work.  

Blue Circle BC86 Power Pillow will not eliminate hum, I own two.
If you believe there is DC causing hum, then try the Emotiva. There is a trial period.

Is your amp tube or SS? Is the hum only isolated to the amp, or does it also play thru the speakers?

Hi John,
If it's mechanical hum, then yes, there are a number of DC eliminators which should work for you.

If you live in a single family home, it may help more to try to eliminate the problem via the process of elimination. Turn off all the other breakers in the house first and see if the problem goes away. 
Best,

E

Hums every time the amp is on?  Yes
Hums no matter the time of day? Mostly in morning and sometimes at night. Very sporadic 
Hums ever since owning the amp? Yes
Any changes to system/house electrical devices? None since purchasing the amp. 

A little more info please...
Hums every time the amp is on?
Hums no matter the time of day?
Hums ever since owning the amp?
Any changes to system/house electrical devices?

Tom