So what's the take-away message with transformer hum?
Some people are more sensitive to hearing the hum, while some are not as sensitive to hearing it?
Some people many have electrical environmental issues (electricity going into house, home electric circuits) that can exacerbate the hum?
Some people are not as sensitive to the hum noise PLUS they have a good electrical environment so they really can't hear the hum?
I said some may be more sensitive to hearing the hum because I wanted to be diplomatic about it, instead of saying things like: you didn't listen careful enough, close enough, room's not quiet enough, you are exaggerating, or worse, you must be deaf
. RichB called me out on that so okay now I am being blunt.., sorry!
Yes, "electrical environmental issues" including those related to the incoming power that you can't do much about it unless it is serious/obvious, or caused by your other devices in the house, are likely the culprit, more often than not.
To your last question, even under the best scenario, that is, the power source is super clean, transformers will still hum but the good ones fed with clean power source will only hum loud enough to be audible with you ears touching the chassis nearest to the transformer. And, all else being equal, larger transformers hum louder.
I posted some links earlier so one can dig into why they hum. Without digging into the details, it should be easy to understand if something vibrates, there will be noise. Obviously transformer core laminate sheets and windings must vibrate with the AC so it will make noise, but the noise could be kept to the point you may consider it "silent".
If you look at Denon's marketing hype about their sand type Aluminum casting filled with resin approach in "eliminating" vibration. That made sense to me and it is believable that such expensive transformers should be near silent, my only issue is with the word "eliminate". If they chose to be more honest, they would have substituted it with "substantially reduce..", or even "minimize", but then I would be splitting hair.
May be its time to agree that if one cannot hear the hum regardless, or can hear it only with the ears touching and with the room under near silent condition, then the transformer is "silent". I am totally fine with that, and I am sure you are as well.
Since your amps are all hum free, and knowing you have much more than 1 or 2 amps, you obviously have clean power coming into your electrical panel, lucky you!
