Hum from a toroidal transformer

[Maciekw]

I have a question for you. What is the acceptable noise level (hum) of a toroidal transformer feeding a power amplifier? Are there any standards?
I ask because I bought an amplifier with purifi modules with an analog power supply. The sound from the speakers is delightful and has a THD+N level of more than 120db, but I can hear the hum from the transformer in between songs (sitting 3.5m away from the amplifier).
The seller to my complaint wrote me back that this is normal! And he himself persuaded me to get the version with an analog power supply because of less noise!
Please help me and point out the standards in this regard.

 

[mhardy6647]

I think that's usually indicative of DC riding on the AC mains input. Toroidal PTs are (particularly) susceptible to a DC offset.
Check the quality of your power. An isolation transformer upstream of the P/S in your power amp would keep DC out, but of course if you need a big one, it will be large, heavy, and expensive.

 

[tmtomh]

I have a question for you. What is the acceptable noise level (hum) of a toroidal transformer feeding a power amplifier? Are there any standards?
I ask because I bought an amplifier with purifi modules with an analog power supply. The sound from the speakers is delightful and has a THD+N level of more than 120db, but I can hear the hum from the transformer in between songs (sitting 3.5m away from the amplifier).
The seller to my complaint wrote me back that this is normal! And he himself persuaded me to get the version with an analog power supply because of less noise!
Please help me and point out the standards in this regard.

Unfortunately you're going to need a DC blocker like this:

HumDinger DC Line Blocker

What the HumDinger will do: Block low-level DC voltage sitting on your AC power line that causes the power transformer to hum or buzz. This type of mechanical transformer hum may be caused if other devices on your power line, or devices on nearby power lines, use AC power asymmetrically. This...

avahifi.com

Linear transformers can mechanically hum from DC on the AC line (as @mhardy6647 notes) - and toroidals, while they have some benefits over other kinds of transformers, are particularly susceptible to DC-induced saturation hum.

 

[DVDdoug]

I have a question for you. What is the acceptable noise level (hum) of a toroidal transformer feeding a power amplifier?

If you can hear it and if it bothers you, I guess it's unacceptable!

 

[jjk1]

I have a few light switch pots around my old house. I had an audible hum from a Yamaha, Marantz, or NAD amp so I knew it was my power. This thing fixed it.

Emotiva CMX2 AC Line Filter With DC Offset Eliminator Review and Measurements

Emotiva CMX2 AC Line Filter with DC Offset Eliminator (Review and Measurements) There has yet to be an AC line conditioner that shows any sort of measurable benefit. One area that hasn't been looked at is the value of DC blocker which can contribute to mechanical transformer hum. While it's...

www.audiosciencereview.com

 

[ppataki]

Post in thread 'DC blocker tryout' https://audiosciencereview.com/forum/index.php?threads/dc-blocker-tryout.57540/post-2135740

 

[popej]

Sometimes a trafo simply hums. It could be production defect or trafo could be designed for lower voltage or higher frequency than actually used. In the later case one can try auto-transformer to reduce supply voltage.

You can try to deal with the problem, but IMHO the hum you hear is well above acceptable. Most of my gear doesn't hum at all, but I have 2 humming devices, where I can hear them only at quiet night. IMO you should sent it back, maybe try SMPS instead.

 

[Speedskater]

a] Is it 24 by 7 all year long?
b] sometimes high AC line voltage can cause this type of problem.

 

[Old_School_Brad]

As others have mentioned, toroidal transformers can be sensitive to "dirty" AC. However, there's also a possibility that the noise is mechanical, caused by insufficient insulation between the transformer and the cabinet. If it's a Class D amplifier, the modules themselves don't take up much space inside. If the chassis is made of relatively thin sheet metal, it could vibrate audibly due to the transformer's movement. Or the transformer is in need of tightening.
Do you happen to have any pictures of your amplifier, particularly the internal layout?

 

[Soniclife]

If you have the option to return it I'd take it. The options that might silence it may take some time to sort out. I try to avoid large transformers now, for just this reason.

 

[Maciekw]

Thank you for all the feedback. Of course, the easiest way would be to send the amplifier back to the dealer. But I bought it in China, paid the shipping costs, customs and VAT. Therefore, this would involve a considerable loss. Therefore, I will first try the DC blocker you mentioned in your posts. And only if it does not work will I take other steps.
By the way, I slightly doubt that this is caused by problems with the grid, because at one time I had high-power amplifiers working in class A at home, powered by high-power toroidal transformers. And at that time I did not hear any hum. Well, but we'll see.

 

[Old_School_Brad]

Thank you for all the feedback. Of course, the easiest way would be to send the amplifier back to the dealer. But I bought it in China, paid the shipping costs, customs and VAT. Therefore, this would involve a considerable loss. Therefore, I will first try the DC blocker you mentioned in your posts. And only if it does not work will I take other steps.
By the way, I slightly doubt that this is caused by problems with the grid, because at one time I had high-power amplifiers working in class A at home, powered by high-power toroidal transformers. And at that time I did not hear any hum. Well, but we'll see.

Which amplifier is it?

 

[Maciekw]

Which amplifier is it?

It is the Cymax 1ET400A-02 Lite MK3. Overall a mechanically well made device. Great, clear and power sound. Comparing to the 3e audio A5 and 3e audio A7 amplifiers, the Cymax subjectively has a much darker background and greater resolution.
The trigger works very well. The lighting of the mechanical switch can be turned off. All in all, this could already be my target amplifier.
Unfortunately, the damned hum from the transformer causes my satisfaction with the buying of this amplifier to sadly disappear. And frustration has set in for me.
Let's hope it's just a DC problem in the grid.

 

[Speedskater]

Get a "Kill-a-Watt" (or similar) AC power meter and check for high AC line voltage.

 

[DanielT]

Is it a hum that comes from the amplifier , transformer itself or is the hum heard in the speakers/headphones?

It's from the amp/trafo itself, it could be as Old_School_Brad mentioned in #9.
When I had a humming sound due to mechanical vibrations between the chassi and the transformer on my Luxor amplifier, I cut out thin pieces of rubber sheets and placed them between the transformer and the chassis. I then screwed the transformer as hard as I could into the chassis. This operation with rubber to reduce vibrations. I kept my fingers crossed and....the hum disappeared.

Slightly blurry pictures of how I did it:


However, if the humming sound comes out in the speakers/headphones so then so maybe, as others in the thread have pointed out, a DC blocker can or might solve that problem.That type of hum is not a problem I've encountered myself (not an annoyingly high level anyway) so I have no practical experience of how good or effective a DC blocker is.

 

[tmtomh]

Except for checking for a loose main transformer retaining bolt (unlikely in a new unit), all the tips and tricks for insulating and otherwise stabilizing a transformer tend not to apply to toroidals. If a toroidal is mechanically humming, it's almost certainly DC in the AC line. Tightening things isn't going to do the trick.

 

[DanielT]

Except for checking for a loose main transformer retaining bolt (unlikely in a new unit), all the tips and tricks for insulating and otherwise stabilizing a transformer tend not to apply to toroidals. If a toroidal is mechanically humming, it's almost certainly DC in the AC line. Tightening things isn't going to do the trick.

Aha toroidal, missed that. Then the amplifier operation I suggested most likely wouldn't be relevant for TS. Unless as you mention: loose main transformer retaining bolt (unlikely in a new unit)

 

[Zek]

If a toroidal is mechanically humming, it's almost certainly DC in the AC line.

Or the toroidal transformer is poorly wound, without a blind winding between the primary and secondary and without protective foil, with poor quality sheets.

 

[wwenze]

I think that's usually indicative of DC riding on the AC mains input. Toroidal PTs are (particularly) susceptible to a DC offset.
Check the quality of your power. An isolation transformer upstream of the P/S in your power amp would keep DC out, but of course if you need a big one, it will be large, heavy, and expensive.

And then the external isolation transformer hums just like the internal one

 

[tmtomh]

And then the external isolation transformer hums just like the internal one

Which is why a DC blocker is the answer.