Mains Transformer Hum, Help!

[Lavawood]

I have a new 100 watt tube amp. I can hear the mains’ transformer 10 feet away. The retailer and manufacturer state hum is normal, from inches away.

During movie dialogue and quiet passages in music, it sounds like there’s a fluorescent ballast in the room.

I’ve tried grounded and ungrounded outlets, with and without the Emotiva CMX2 which they kindly let me “borrow”.
I really don’t want to get rid of the amp. I’d rather not subject myself to the subjective opinion of a warranty review and all the shipping cost and risk.

can a transformer be built that is quiet? Is there anything else I can try short of locating the amp in another room or enclosure?

Any help would be appreciated!

 

[ta240]

The actual transformer is vibrating?

Yes, there are quite ones. But even some of the good brands will have ones that make noise from time to time. I think the main problem is the metal laminations that make up the center part of it can have tiny spaces that allow them to vibrate.

 

[solderdude]

As an experiment you could loosen the transformer and put it in there on rubber or sorbothane feet in case the transformer couples mechanically to the enclosure. When this works you need to find a way to mount it on dampers.

The transformer most likely has multiple windings so an alternative may be hard to find.
Chances are a toroid could hum less. Having one made to specs (the needed windings) could be expensive.

 

[Speedskater]

Some possible causes:
a] High AC line voltage, especially with tube products. Many legacy and boutique amplifiers were designed for lower line voltage. Check with a "Kill-a-Watt" type meter.
b] Transformer has loose the metal laminations. I have replace the thru-bolts with stronger stainless steel bolts (non-magnetic) that can be tightened more.
c] DC offset. In a residential setting, this type of problem is seldom 24 by 7.

 

[Count Arthur]

My two power amps have large toroidal transformers. One will hum a little more than the other when they're first powered on, but they both usually settle down after a few minutes and get much quieter, if not totally silent.

Some times they are noisier than others, which makes me wonder whether it's something else attached to the mains, either in my house or nearby; maybe due to DC offset:

https://www.pooraudiophile.com/2015/03/how-to-fix-dc-offset-and-transformer.html

https://www.wikihow.com/Measure-DC-Offset

 

[Lavawood]

That’s a good idea. I used to mount my hard drives on rubber washers. I’m going to try this.

I’m also going to try to find somewhere local with “cleaner” power, to plug it in and see if my house power is an issue.

I have a quote from mercury magnetics; $250 and 3 months...they would dissect the stock part and recreate it. The result may or may not be better. I’m hoping there’s another way.

 

[DonH56]

I see big washers mounting the transformer so there may be compression rubber/Si/whatever bushings under them already. They may have been tightened down for shipping and simply need to be loosened.

It could also be a bad transformer...

 

[Count Arthur]

I have a quote from mercury magnetics; $250 and 3 months...they would dissect the stock part and recreate it.

Do you know what the secondary windings output voltages are? Generally you don't need to "dissect and recreate" a transformer, you just need to know what size it is, the VA rating, the primary input voltage and the secondary output voltage, or voltages, if the transformer has multiple secondary windings.

Many transformer manufacturers will supply custom wound transformers for specific, not "off the shelf" values:

http://www.canterburywindings.co.uk/index.html
http://sigatransformers.co.uk/
https://www.plitron.com/
http://www.amethyst-designs.co.uk/index.php
https://airlinktransformers.com/

 

[Lavawood]

Thank you!

 

[Dimitri]

b] Transformer has loose the metal laminations. I have replace the thru-bolts with stronger stainless steel bolts (non-magnetic) that can be tightened more.

I see what looks like plastic washers on the lamination screws. The screws can't be "that" tight with these washers there.

 

[Dimitri]

Is there anything else I can try short of locating the amp in another room or enclosure?

Here is a "buzzkill" video:

You have some decisions to make ...

 

[Speedskater]

I see what looks like plastic washers on the lamination screws. The screws can't be "that" tight with these washers there.

When I did it, the washers were fiber. But SS washers over the plastic washers might work.

 

[Count Arthur]

How old is the amp, is it still under warranty, or can the manufacturers supply a replacement transformer?

You could try replacing those plastic washers with stainless ones and tightening the bolts.

 

[Lavawood]

Here is a "buzzkill" video:

You have some decisions to make ...

That’s it!
Thank you!

I don’t have a big enough clamp, but if I squeeze the transformer between my palms it stops humming!
I’ll work on a bolt / washer combo that kills it.
Love this website.