Transformer hum - is it normal?

[BM1]

I just noticed yesterday a very quiet hum that emits from my receiver when it's powered on. It's coming from the transformer I believe. I assume this is normal but wanted to see if anyone else had noticed it on theirs.

This a cheap $400 receiver, but it has been connected to an APC power filter since new.

 

[PENG]

They all hum, everything else being equal, some hum quieter than others. I find Denon AVRs tend to have quieter ones regardless of price. Toroidal ones hum as well. I consider it acceptable if I can only hear the hum by sticking my ear close to or touching the chassis.

 

[BM1]

That's what I figured. Thanks for the info.

 

[DS-21]

They all hum, everything else being equal, some hum quieter than others.

No, they don't.

I would return any AVR or amp that had audible hum. And by "audible" I mean "with your ear in front of the faceplate."

Then again, perhaps I'm more sensitive to HF noise than most. I think one of the reasons I don't care about video is because most of TV's common when I was a child (CRT's) gave me - and still do - bad headaches from transformer hum.

 

[PENG]

No, they don't.

Don't be so sure.

Then again, perhaps I'm more sensitive to HF noise than most.

Well, sensitive to HF or not, if you are sensitive enough to frequencies in the range of 100/120 to 200/240 hz you should be able to hear the humming noise. Transformers used in audio equipment such as power amplifiers are typically very quiet but typically you can still, though barely, hear the best ones with you ear touching the enclosure. There are some that are louder, next time you visit a AV dealer you can try them out if you are curious enough. Nothing to do with ground loops, you can hear it with nothing connected, just the power cord.

 

[TLS Guy]

I just noticed yesterday a very quiet hum that emits from my receiver when it's powered on. It's coming from the transformer I believe. I assume this is normal but wanted to see if anyone else had noticed it on theirs.

This a cheap $400 receiver, but it has been connected to an APC power filter since new.

No, its not normal, but common. The essential information is cheap receiver, and the price quality ratio of the components is the crucial element here.

I do not own any units that have noisy transformers.

The early series Quad 405 amps back in the 70s had noisy power transformers, due to shoddy work from a supplier. These were replaced.

That had been my only experience with equipment I have owned that had noisy power transformers.

 

[M Code]

Basic question is will it get any worst..
A transformer should not hum..
Is the hum audible with the volume control in the minimum position..
Or is the transformer noisy due to loose laminations and/or mounting..

Just my $0.02...

 

[Adam]

No, its not normal, but common.

I think being "common" makes it normal.

I'm not saying it's good, though. The torroids in my amps hum, and I hate it.

 

[TLS Guy]

Basic question is will it get any worst..
A transformer should not hum..
Is the hum audible with the volume control in the minimum position..
Or is the transformer noisy due to loose laminations.

Just my $0.02...

Yes, generally it will get worse over time. A noisy transformer is an improperly laminated one. The constant vibration further loosens them and it does worsen slowly over time.

 

[TLS Guy]

I think being "common" makes it normal.

I'm not saying it's good, though. The torroids in my amps hum, and I hate it.

Another of the many failings of Far Eastern manufacture. The wonderful Partridge transformers of a half century ago, never had this problem.

I'll say it time and time again, you generally get what you pay for.

 

[M Code]

Yes, generally it will get worse over time. A noisy transformer is an improperly laminated one. The constant vibration further loosens them and it does worsen slowly over time.

That is why we raised the point..
The power transformer should not hum and should not vibrate due to low quality assembly..

Return and exchange the unit under warranty.

Just my $0.02..

 

[PENG]

Gents, they all hum, some are built for quietness but still hum if you are close enough to them in a quiet environment. I agree if you can hear the hum easily, say from a few inches away, then may be it is not "normal" but hum they do.

I can hear the fan of my Oppo well before I can hear any of the toroids in my 4 amps and I consider them normal.

It is a matter of how audible the hum is and at what level is it considered normal. That would depend on the design, build quality, size, mounting, enclosure, and finally each individual's sensitivities to the fundamental and harmonics of the power frequency.

 

[3db]

No, they don't.

I would return any AVR or amp that had audible hum. And by "audible" I mean "with your ear in front of the faceplate."

Then again, perhaps I'm more sensitive to HF noise than most. I think one of the reasons I don't care about video is because most of TV's common when I was a child (CRT's) gave me - and still do - bad headaches from transformer hum.

Transformer hum is humming at the line frequency which ranges from 50 to 60 Hz, far from high frequency. Like PENG said, transformer hum is inevitable.

 

[3db]

Yes, generally it will get worse over time. A noisy transformer is an improperly laminated one. The constant vibration further loosens them and it does worsen slowly over time.

Incorrect assertion. My Technics receiver's transformer hums since the day I bought it and it has not gotten worse. I've had that reciever for over 10 years now. I also had Radio Shack integrated amp whose transformer also hummed but it never got louder after 20 years.

 

[TLS Guy]

Transformer hum is humming at the line frequency which ranges from 50 to 60 Hz, far from high frequency. Like PENG said, transformer hum is inevitable.

It is not inevitable. I have just not only put my ear right against each of my Quad 909s, and the two Quad 405 IIs but I have been all over them with my stethoscope. There is not a trace of hum to be heard.

If the coils are wound good and tight and the laminations can't move and are secure there will be no hum. Something has to vibrate to make hum.

If you build it solid so it does not vibrate there will be no hum.

And yes, in general this is a fault that gets worse over time, that does not mean it gets worse in every case.

So I will state for the record, that good power transformers do not hum.

If you can hear hum on your units, then corners were cut by using substandard components and I bet that the power transformer is not all that is substandard.

 

[3db]

We all know your generalizations and opinion on AVRs Just because your QUAD amplifiers exhibit no transformer hum doesn't mean xmfr hum doesn't exist with other quality seperates. OPPOs are no slouch but they exhibit transformer hum as reported by PENG.

 

[M Code]

In the price-competitive, commodity category of AVRs, the power transformer is the single most expensive internal component...
Next, guess where the 1st place they cut the cost to save $...

Next question..


Just my $0.02..

 

[jonnythan]

It is not inevitable. I have just not only put my ear right against each of my Quad 909s, and the two Quad 405 IIs but I have been all over them with my stethoscope. There is not a trace of hum to be heard.

If the coils are wound good and tight and the laminations can't move and are secure there will be no hum. Something has to vibrate to make hum.

If you build it solid so it does not vibrate there will be no hum.

And yes, in general this is a fault that gets worse over time, that does not mean it gets worse in every case.

So I will state for the record, that good power transformers do not hum.

If you can hear hum on your units, then corners were cut by using substandard components and I bet that the power transformer is not all that is substandard.

No matter how solidly you build a transformer it will vibrate.

 

[PENG]

Once in a while I have to say the "with all due respect........ to TLS guy (because I respect the guy ), but like 3dB said...........we know how he is like, sometimes.

Anyway, I too, would state on record again, that transformers do hum, you may not hear them but others may and better designed/built ones would be hardly audible under most conditions. I had purposedly visited more than one high end dealers in order to listen to those hums and found even high end ones that you would not expect them to cut corners, had transformes in them that hummed. I am not going to mention names for the obvious reasons. I bet I can hear that Quad without playing doctor, but if TLS guy cannot hear it with his doctor's instrument then I suspect there may be other reasons but I'd rather not go there. My AV7005 is very amazing quiet and I think incapsulating the transformer might have help. There are ways to migitate the inherent noises, but would be practically difficult to eliminate them.

For those interested, go visit a high voltage substation and tell me if you could hear those >150 MVA transformer yelling at you over the fence at the power line frequency and the associated harmonics (predominantly 2nd). Pick an off peak period so the cooling fans won't be running. And yes, stick with GE, Westinghouse, ABB to make sure they are made by reputable companies.

Like GE, ABB is a highly reputable company, follow the link you can read about how they talked about trying to "reduce" transformer noises, they did not talk about eliminating them.

http://www04.abb.com/global/seitp/seitp202.nsf/0/968e648efc0fd948c12574eb0048eb14/$file/The+Sound+of+Silence.pdf

Those are large power transformers, but the principles remain the same. You can wrap the coils tight, but they still move and all we can do is to try mimizing noise to the point it won't bother us. Of all the amps/avr I own and owned, there was one that I could hear from about a foot away, that's what got me curious to visit high end stores to find out for myself whether I should returned that unit or not. After bench marking the best I could at the time, I decided not to bother returning it.

I have the feeling that this has become an argument mainly between those who have some background in electrical engineering or physics. For other normal people, they must be wondering why we are wasting time debating something that is not an issue in real life, like THD, <0.02%, but >0.01%, is that normal or not, who cares?

 

[PENG]

In the price-competitive, commodity category of AVRs, the power transformer is the single most expensive internal component...
Next, guess where the 1st place they cut the cost to save $...

Next question..


Just my $0.02..

I always appreciate your insider info on the commercial side but for something technical I won't waste my time debating you so yeah, next question, like you said.