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How deadly is transformer hummm...

Hello Folks,

I recently collected a lightly used (less than 50 hours) Dennis Had - Inspire - "Fire-Bottle." Within some few days, I noticed a humm emerging from somewhere within the chassis of the unit. As the unit was sold in "perfect" condition, I found the humm startling. Mind you, I've discovered absolutely no evidence confirming the sound is compromised; I mostly hear the sound within a couple feet of the amp, when the surrounding environment is silent.

This amp truly is a work of art. Nevertheless, I am now dealing with this 'humm' sound. I bought an Emotiva CMX-2 as a way to deal with DC offset, and this has not impacted the situation to any detectable improvement. Perhaps there is a slight improvement, but negligible. What to do?? Should I just relax, shake it off, and assume the amp will live well, or a down-the-road transformer replacement will simply become part of my experience with this amp? Should I put pressure on the seller to "right" the situation? He claimed, as I asked him, that it was the quietest amp he's ever owned. His add boasted that the fire-bottle exceeded amps from Pass Labs, a Cherry Amp, and one other that escapes memory. The seller has presented all of his communication in the manner of friendly professional etiquette. 

Your thoughts are appreciated. 
listening99
atmasphere's avatar
atmasphere
11,585 posts
 
Since this amp employs an EI core power transformer, DC on the line really won't affect it. But if the cores are not secured properly, it can vibrate.

The four screws on the power transformer at each corner might simply be loose. Its worth it to see if tightening them makes the transformer quieter. This probably can be done fairly easily. Of course the amp should be unplugged from the wall, and to best do this the bottom cover removed. If any of this sounds at all tricky, take it to a qualified technician.
listening99 OP
172 posts
 
@bdgregory the hum is not audible from the speaker drivers. This is a mechanical event, coming from within the chassis. 
@brownsfan how do I detect tube issues like you describe- microphonics, etc?

@stereo5 I always enjoy the humming of my wife, but it seems her tone is at a much higher frequency.

I’m running the amp with a DAC and a CD transport... is it ok to unplug the RCA cables from the system, to rule out those components while this tube amp is on? I hear you don’t want to run a tube amp without connections...
twoleftears's avatar
twoleftears
5,313 posts
 
Hum can be caused by DC offset, ground loop, simple transformer mechanicals (loose nuts, etc.), or a poorly wound transformer or one that's degraded.  Google PS Audio + hum + eliminate for a simple guide. Some hums are easily dealt with, and some can drive you up the wall.  Occasionally the only solution is to have a brand new transformer installed. 
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mrdecibel
2,900 posts
 
Humming is the obvious choice, when you do not know the words....lol.....Seriously......The truth of all transformers...... they all hum, radiate noise ( Toroids produce less than E-I core ) and exhibit, some amount of vibration, as well. I believe all transformers should be separated / isolated from the chassis, as the older HK Citation power amps ( the model 12, 16 and 19 ) had / have. I have modded hundreds of transformers from various audio products by isolating the transformers, with excellent results in sq ( from the speakers / system ), and lower noise from the chassis. Rubber grommets, Dynamat, roofing repair tape, cork, as well as many other materials, can be used. Be safe, and well. Enjoy !
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