Do all toroidal transformers hum?

Help Gurus,

When I put my ear (about 2 inches from the top)to my integrated amplifier, I can hear a faint hum from both the transformers. Can't hear anything when I move my ear away from the amp. Is this normal?
It doesn't sound normal to me, at least I have never tried it. The bigger question is "do you often listen this way". If not I wouldn't worry about it.
Yes, it is quite normal. If you cannot hear it unless you are that close, forget about it. On big amps with modern transformers toroidal or iron core, you get humm. Many manufacturers cover transformers to reduce audible hum or soft mount them to do the same. Top quality transformers do not hum.
Thank you all for the responses, so you think most of the amps carry mediocre trannys?

The question is, does the slight hum have any practical effect. While the best transformers may not hum having one that makes the slight noise yours does does not mean that it is a bad transformer or that performance is necessarily bad. There are components where everything has been selected with cost no object and they are very expensive. Good designers select components that will do a good job at a reasonable price, if you are happy with the performance otherwise don't worry.
Hum is just 60 Hz and 120 Hz vibrations within the transformer. There is probably a subtle effect of these vibrations on the ac wave, but you are right it has little effect. Yes companies frequently buy marginal transformers to assure a price point. You get what you pay for.
Thank you Stanwal and Tbg, that was informative. The funny thing is that I had Denon POA 2400 (200W/channel) not a sign of hum, but the DK does have a faint hum. I guess I have to live with it as it's not audible 3 inches away from the amp. The Denon had a cheap 2-pront (no earth) power cable, do you think the grounding might be an issue? I had a B&K MC 101 Pre-amp with a IEC power cable and that had a hum too.
I had significant hum problems with my Karan K180 amp. Much to my suprise, changing the power cable made a big difference, not sure why, might be worth a try.
How did you get from "can't hear any hum more than four inches away"... to.... "All toroids are inferior?".

If you aren't wearing the amps as headphones the hum issue should pose no significant issues.

Certainly, if you have toroids in your amps and don't like your amps... perhaps only those toroids in your own amps are inferior.

Relax. Don't sweat the petty stuff, but do remember to pet the sweaty stuff now and then.

Stan outlined it pretty well already.
Toroid trans usually hum way less than a standard shape. One point might be to tighten the bolt holding it down. The usual deal for toroids is a bolt down the middle.
By the way, the fact they put in a toroid means they spent MORE MONEY than they had to: the toroid cost more than an ordinary transformer. (for the same voltage/ etc) Of course, maybe they got a deal an a couple tens of thousands of crappy toroids??
The reason for the hum is what is called magnetostriction. You can read about it here.

It may also be sensitive to the tightness of the transformer mounting screws, and to the design of the mounting arrangement, which might influence the degree to which the vibrations are amplified or damped by the surrounding structure.

-- Al
Almarg, don't forget dc in the line and poor construction.
You may also help by using either coupling or isolating devices under your amp. Although they work on opposing principals I have found both to improve the sound to a surprising degree. I have been using Audio Points from Star Sound but am now using FIM isolation devices [modified] under all components. But there are many others.
Thank You all for the great advices. Just want to make sure that the hum is not going to damage anything (I'm new to this stuff,so please pardon my ignorance). The DK does have covers on it's transformers.
I would not worry about hum that is audible only two inches from the top of an amp. Virtually any toroidal transformer, even of the best quality, will buzz to some degree if the DC level on the AC power line is high enough.
A friend who suffered with this problem, only to a much greater degree, told me of this thread. Most of what has been said is fairly accurate. DC on an AC line in excess of 1 volt makes a toroidal transformer hum. Also, as has been pointed out, most transformers hum - magnetic flux in action. However, when it is audible it is excessive. It really has to do with how the transformer was wound. In addition to power conditioners with huge toroidal transformers, we make a DC blocking power cord that has thus far been effective in eliminating hum in the excess DC situations. I am not here to hawk my products, but if you have an interest, just ask.
Thanks Gbart, the fact that my B&K MC Pre-amp with external power supply also had a faint hum (again when I put my ear to the power supply), does that indicate a DC presence on the AC line?
Dstandard, where can I find your product catalog?
I made a DC blocker as a favor to an Audiogon member a while back. There are a could of circuits floating around the Internet. Its easy enough for anyone with decent DIY skills to accomplish, just remember you're working with electricity.

Nice work Gbart, unfortunately I absolutely have no knowledge of electrical circuits.
Livin....Try I can surely attest to the build quality and effectiveness of these products.
I see someone beat me to the reply, but the website is The name is Dave Stanard.
Not all, but some.
Amplifier hum problem SOLVED!!!. Gbart was kind enough to make me a simple DC blocker (with high quality Caps and resistors). I received it last night, I plugged the amp into it and VOILA NO MORE HUM. Not even a hint of it. I pressed my ear against the amp. to hear the faintest hum, but nothing, absolute SILENCE. You won't believe how much the DC blocker from Gbart costed... $72. Yes it's just Seventy Two dollats.

It was actually caps and a diode bridge, not resistors. :-)
Well Gbart, I told I was a novice :-))
Yes, Try putting neoprene under it. Tweaker
Here, Two types of possible noise here:

(1) On the sub issue, it is mechanical vibration. The transformer probably needs tightening or damping using some sort of rubber, or it is a crappy transformer and buzzes internally. I don't buy the "DC on the AC" theory.

(2) On the Ampzilla issue, you don't say if the noise is through the speakers or mechanical noise at the amp. This would be helpful.

Toroidal Transformer in IndiaPower Transformers in India
My big American made, 600VA AnTek in my F5 isn't cheap and it does indeed hum exactly as you describe. You basically need to have your ear in the case to hear it, but it makes a grunting you can hear 3 feet away when you turn it on.