How deadly is transformer hummm...

I want to update this thread, bring it full-circle, so to speak.

I was able to finally develop a conversation with Dennis Had, who built the amp. He asked for a picture of the amp, which has been sitting on a thick slab small side-table type of stand, or pseudo-stand... He then asked me to put the amp on my kitchen counter and plug it in... he said the Inspired design is stable, doesn't need speakers, so I didn't have to haul any other equipment into the kitchen. 

The amp was noticeably more quiet in the kitchen. 

He then suggested I buy some sound coat, or similar product, claimed that the wood stand acted as a wood resonator, much like a piano. 

This is great news, because it's a wonderful piece of equipment and I've got some new open baffle speakers on order, which should complement the amp nicely. The speakers are based on the F-15 Lii Audio driver and boast 97db efficiency.

This will be a single-driver setup - I'm thirsting for a vast soundstage!

Thank you all, for participating in this discussion... 

Also if the amp only has 50 hrs on it it's possible the hum may go away to some extent with further run-in.  My Line Magnetic amp hummed slightly at first but after 60 hrs or so it pretty much went away except during the initial 10 minutes of start up.  Once it gets warm and presumably the transformers expand a bit everything becomes dead quiet.

The OP asks how deadly is transformer hum. With only a little bit of exaggeration, I feel transformer hum might have significantly lowered risks to my life:


I have a class A tube amp. A little bit of transformer noise when up close, but nothing to annoy or out of the ordinary IME. Earlier this year, I moved out of the new-ish apartment building I was living in when I bought the amp into an old house. Now the transformers were humming loudly. I tried new tubes I had in reserve. I tried tightening the transformer mounting bolts. I tried a couple of DC blockers. No improvement. I checked voltage — consistently within a half volt of 123v at different times and at different outlets. 

A clue that the house wiring might be an issue came from noticing that the equally-annoying hum from the speakers was reduced after switching off all other circuits (but still no reduction in mechanical transformer hum).

I gave a call to the owner of a local audio shop from whom I had bought speakers and sources. To his credit, he referred me to his electrician, rather than different amps or power treatments. Long story short, the electrician replaced the corroded meter box and exterior wire, the ancient and miswired electrical panel, the grounding rod (with two), all of the outlets and switches (removing a bunch of dimmer switches), and some old interior wiring (where it appeared that high current draw had nearly started a fire). In the course of that, he removed some weird junction boxes in between the meter box and before the electrical panel, fixed phase miswiring and shorts in a few outlets I had not yet used, and redistributed load at the electrical panel. 

The result? Not exactly silence, but the same faint mechanical hum as when I bought the amp, and equally low noise at the speakers. 

So, despite what you are told by some (@cakyol), mechanical transformer hum is not always because of mechanical issues. An amp that works fine at the factory bench can misbehave when fed AC with loads (literally) of harmonics on the line. I would recommend trying all the nearly-free options I tried above. If you can, I would highly recommend following @jea48’s advice to see how your amp behaves connected to a couple of different mains power sources. (A techie’s would be ideal if you don’t mind paying the inspection fee, but a friend’s in a newer house in a different neighborhood would also be useful.) 


How did the hum improve my odds of survival? About a week after the electrical work was done, we had several nights of intense thunderstorms and strike lightening. I sure felt more secure knowing that I had new grounding rods and a whole-house surge protector, and that several wiring faults had been rectified — which I probably would not have had done were it not for going all out to fix the transformer hum. 
Best of luck in your quest for (good) silence.