Transformer hum - is it normal?

P

PENG

Audioholic Slumlord
OPPOs are no slouch but they exhibit transformer hum as reported by PENG.
Thanks for the support but may be I said it wrong, I meant to say I heard the fan and could not hear the transformer. I did not try to hear it without the fan being on. Minor detail really, smaller transformers tend to make smaller noise as there will be less windings and core laminations to move around.
 
TLS Guy

TLS Guy

Seriously, I have no life.
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:D.

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:D. 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?
Because it is an issue in real life. Transformer hum from the AC line is a problem in audio equipment. It has been known for years, and solutions have been known for a long time.

A transformer in an audio device, has one of two or both of these problems.

1). It is poorly constructed.

2). It is operating close to saturation.

Harold J. Leak was obsessed with this problem 60 years ago and worked with Partridge to make some of the finest transformers the world has ever seen.

I have carefully assessed the issue in equipment here.

The Quad 909 amps are silent even when listening with a very high quality Litman medical stethoscope. The transformer is fixed to the upper case and I listened right over it. Totally silent, the same for the 405.

Quad 33 pre amp, silent. Quad FM 4 very slight hum just audible with stethoscope.

Marantz 8003 pre pro, listening over the transformer totally silent.

Marantz SACD player, silent.

Oppo BD 83 silent. By the way since this is in a rack with good ventilation, I have never seen the fan operate, and if it does I have not heard it.

All my crossovers are silent, and one the Crown has its transformer external on the back panel.

Revox A 700. This has a huge transformer for moving the big 10.5 inch reels fast, and other duties. No hum with the ear close, but easily heard with the stethoscope.

Brenell Mark 6. This also has a huge transformer for moving the large 10.5" reels. This transformer was accessible with and I could lay the stethoscope right on it and its silent.

Revox A77, no hum audible, but you can not stop the capstan. The sound of the capstan was just audible with the stethoscope.

As above for the NAK cassette deck.

I would never put up with a unit were transformer hum was audible by the unit.

The most serious cause of transformer hum is under sizing, as this will affect audio performance.

I have had to pursue my power company previously for this problem.

When I paid to have my power cable buried last year, Beltrami electric agreed to oversize the transformer 26% over any conceivable load, because of my critical requirements. By the way that transformer is also silent and does not buzz, probably because of over sizing.

For equipment I build, I use Canadian Plitron transformers, they are absolutely the best.

I have found the paper, I was looking for and have now put it on my computer, which is a fantastic study of mechanical noise in transformers.

You can protest all you want and insult me all you want, but I know darn well audible transformer noise can and should be eliminated from consumer products. And I will continue to stand by that.

In closing, I would say there is a growing tendency to excuse the shortcomings of the abundant junk pushed on these forums.

That is not a good thing. It lets the manufacturers off the hook, when they need to be hounded. It mitigates against improvement at every level where it is badly needed.

Never tolerate the substandard, and never be satisfied with the status quo.
 
P

PENG

Audioholic Slumlord
For some reason I can't read the paper you link at the moment. I would think that if we try hard enough we could perhaps reduce core/wdg noises to an audible level. To consider a transformer that is barely audible with ear sticking to it as sub standard is too extreme imo but we can agree to disagree.
 
TLS Guy

TLS Guy

Seriously, I have no life.
For some reason I can't read the paper you link at the moment. I would think that if we try hard enough we could perhaps reduce core/wdg noises to an audible level. To consider a transformer that is barely audible with ear sticking to it as sub standard is too extreme imo but we can agree to disagree.
I'm not talking about putting your ear on the case. I'm talking about mechanical noise audible in the vicinity of the unit or in the room as a whole. You will find that commoner than you think.

In terms of whether any amount of buzz is audible or not and is a significant problem depends on its cause. If it is due to core saturation then it will be significant and affect overall performance of the unit.

Transformers for audio equipment should always be over sized and never under or specked to the knuckle.

Let me try the link again. It is a very good paper.
 
P

PENG

Audioholic Slumlord
I just read it quickly, and it stated that power transformer should be dead silent ....but totally different in reality. Well I am fine with that kind of statement. It is like forum posters should be nice to each other at all times but reality is different. After the introduction it went on to explain why transformers make noise, ways to measure and to reduce the noise. Again, that science, not ones own belief what it should be.

By the way you used the word 'protest' yet I don't protest when I am stating scientic facts and sometimes my informed opinion. Also you are entitled to your opinion as I am to mine so there is no need to think in terms of some sort of 'protest' regardless.
 
P

PENG

Audioholic Slumlord
I'm not talking about putting your ear on the case. I'm talking about mechanical noise audible in the vicinity of the unit or in the room as a whole. You will find that commoner than you think.

In terms of whether any amount of buzz is audible or not and is a significant problem depends on its cause. If it is due to core saturation then it will be significant and affect overall performance of the unit.

Transformers for audio equipment should always be over sized and never under or specked to the knuckle.

Let me try the link again. It is a very good paper.
Well if you put it that way then we seem to be more or less in agreement. Nice surprise and happy ending! Talk about communication problems..

Thanks for the paper, it is a good read. The ABB one I linked is about large power tx, yours is for the much smaller ones that we are talking about though the topics are pretty much the same, all about the need to reduce and how.
 
TLS Guy

TLS Guy

Seriously, I have no life.
Well if you put it that way then we seem to be more or less in agreement. Nice surprise and happy ending! Talk about communication problems..

Thanks for the paper, it is a good read. The ABB one I linked is about large power tx, yours is for the much smaller ones that we are talking about though the topics are pretty much the same, all about the need to reduce and how.
As I read BM1's post I guess his complaint is not clear. But I took it to mean that he could hear hum when in the vicinity of the unit. May be he would be good enough to clarify and be specific about his complaint.

Ah yes! Communication problems.
 
D

DS-21

Full Audioholic
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.
While in theory you're correct, in practice if a theoretical phenomenon is only observed at de minimis levels, for all practical purposes it is non-existent.

FWIW, I listened for transformer this evening. No stethoscope, just ear on unit. Results:

Anthem MRX 300 AVR, ear on front panel and ear on the top panel over the (EI core) transformer (which was surprisingly hot...): no audible hum

miniDSP power supply (old Palm Pre USB adapter, ~5V SMPS): no audible hum

Electrovoice CPS 8.5 Class D amplifier (SMPS; run in bridged mode for subwoofers, rated 1kW/4Ω/4ch driven): hum barely audible through front-panel fan vents.

Snell SPA-750 subwoofer amp, from front panel and over the (toroid) transformer: no audible hum

Oppo BDP-83, ear ~1" from front panel (only part that is accessible): no audible hum

Meridian 551 Integrated amp, ear on front panel and (glass) top panel above (toroid) transformer: no audible hum

Wall wart for KEF Picoforte iPod dock/amp (SMPS): no audible hum

KEF Picoforte mini-amp: hum slightly audible with ear against top of unit

AppleTV2, top of unit: no audible hum

HeadRoom Total AirHead Mk. 1.5, on AA batteries: no audible hum

HeadRoom Portable Micro Amp (2008 version), on its internal LI batteries: no audible hum

Tannoy i30 iPod dock/boombox (BASH amp, presumably SMPS): hum slightly audible from vent at rear of enclosure.

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.
Sadly, one generally cannot expect solid engineering from the so-called high end...

(Obvious exceptions: McIntosh, Bryston, Boulder, Meridian, and like quality-focused firms.)

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?
Problem is, quality control in audio kit generally it so appallingly lax today, that audible and distracting transformer hum is often a real issue.

If a unit's hum was audible from a foot away, no question that I'd return it. I wouldn't want such a thing in my home. (That kind of thing is why I generally source my audio gear locally, rather than from internet venders. I don't want to pay return shipping to cover a maker/marketer's lax QC.) Though many units I've heard at so-called high end dealers have whined much louder than that.
 
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3db

3db

Audioholic Slumlord
Thanks for the support but may be I said it wrong, I meant to say I heard the fan and could not hear the transformer. I did not try to hear it without the fan being on. Minor detail really, smaller transformers tend to make smaller noise as there will be less windings and core laminations to move around.
No PENG, You didn't say it wrong. I read it wrong. I went to review my post but got interupted with work and I was unable to correct it. :eek:
 
3db

3db

Audioholic Slumlord
If a unit's hum was audible from a foot away, no question that I'd return it. I wouldn't want such a thing in my home. (That kind of thing is why I generally source my audio gear locally, rather than from internet venders. I don't want to pay return shipping to cover a maker/marketer's lax QC.) Though many units I've heard at so-called high end dealers have whined much louder than that.
I would agree with you that if I heard a xfmr hum over a foot away, I would return the unit. There is definately something wrong. I'm talking about xfmr hum when your less than a foot away from the unit. I can hear my receiver when I turn it on when I'm right next to it. However, I don't hear it if I had turn it on with the remote and then moments later mover close to it. I think its the audatory memory at play. I also don't hear the xfmr hum of my receiver whgen standing beside it when my BluRay player starts to spin a disc that has been loaded into it.
 
B

BM1

Audioholic Intern
Regardless of whether transformers should or shouldn't hum, it sounds like there are a lot of current model receivers on the market including high end units that exhibit at least some audible hum if you get close enough and listen. There was a thread on another forum discussing someone that went to an audio shop and listened to some low-mid grade receivers and then some high end receivers for transformer hum, and they all had almost equal levels of audible hum regardless of price.

It seems like avoiding hum altogether would mean auditioning every receiver you're interested in and picking the one you found most acceptable. High price and name brand don't gaurantee silent operation, apparently.
 
AcuDefTechGuy

AcuDefTechGuy

Audioholic Jedi
So the take home message is: Hell, no, loud transformer hum noise is Not normal.:D
 
cpp

cpp

Audioholic Ninja
Just to make this simple, if you hear HUM and don't like it, return the unit.
 
slipperybidness

slipperybidness

Audioholic Warlord
I haven't seen this much discussion on a hummer since Clinton was in office :D
 
TLS Guy

TLS Guy

Seriously, I have no life.
Just to make this simple, if you hear HUM and don't like it, return the unit.
I think that is basically a good rule. However a couple of caveats, if the noise is due to a poorly designed and constructed core then it may get worse.

If the noise is due to saturation, that is bad, and will affect performance.

I wish I could tell you how to tell without instruments, but I can't think of a way.

The high end is a different matter. If it hums the units is not high end just made to look high end. Remember, there are only two causes for this, poor design and construction, or under sizing. If either or both of these exist it is NOT high end.

Unfortunately the subjective, no science round me audiophools, are easy prey for mutton dressed up as lamb.
 
3db

3db

Audioholic Slumlord
I think that is basically a good rule. However a couple of caveats, if the noise is due to a poorly designed and constructed core then it may get worse.

If the noise is due to saturation, that is bad, and will affect performance.
Saturation would indicate to me that the transformer is grossly under specced for its intended application; ie..asking the power supply more power than what is designed for.
 
TLS Guy

TLS Guy

Seriously, I have no life.
Saturation would indicate to me that the transformer is grossly under specced for its intended application; ie..asking the power supply more power than what is designed for.
Basically that is the case, although running a transformer right up to spec, is not a good idea. Good practice requires an overage of at least 25%.

Trouble starts as you approach core saturation.

Receivers again! But the all channels driven being lower for each amp than 2 channels driven, is I'm sure at least partly due, or may even wholly due to this issue.
 
D

DS-21

Full Audioholic
It seems like avoiding hum altogether would mean auditioning every receiver you're interested in and picking the one you found most acceptable. High price and name brand don't gaurantee silent operation, apparently.
That is right, unfortunately. Well, mostly. Sample-sample variation within a given model is an issue, too.

The high end is a different matter. If it hums the units is not high end just made to look high end. Remember, there are only two causes for this, poor design and construction, or under sizing. If either or both of these exist it is NOT high end.
There's no way for the consumer to really know the difference.

For example, take the Pass Labs INT-150.

A seven thousand plus dollar integrated amp from a man considered in audiophile circles an amplifier savant (and who does have some good amps under his belt, such as the Adcom GFA-5800 I've owned since undergrad) with inferior performance to a typical $350 AVR. That, of course, gets rave subjective reviews from Stereophile et al.
 
P

PENG

Audioholic Slumlord
A seven thousand plus dollar integrated amp from a man considered in audiophile circles an amplifier savant (and who does have some good amps under his belt, such as the Adcom GFA-5800 I've owned since undergrad) with inferior performance to a typical $350 AVR. That, of course, gets rave subjective reviews from Stereophile et al.
I don't know if the toroidal in my GFA-555 is "good" overall but it certainly is one of the quietest one in my collection. I have to press my ear against on the enclosure in order to barely hear it.
 
P

PENG

Audioholic Slumlord
Basically that is the case, although running a transformer right up to spec, is not a good idea. Good practice requires an overage of at least 25%.

Trouble starts as you approach core saturation.

Receivers again! But the all channels driven being lower for each amp than 2 channels driven, is I'm sure at least partly due, or may even wholly due to this issue.
FYI, in all my bench mark listenings the thing would not be driving any speakers, in most cases it would have just power cord plugged in with nothing else connected. So in such cases underdesign would not be a factor.
 
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