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?
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.
