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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

Showing 6 responses by atmasphere

atmasphere's avatar
atmasphere
12,104 posts
 
Would 248F handle the temperatures within the amp
No worries.
Oh, I will include this marvelous detail about the amp's design: "The transformers are made with grain orientated steel and impregnated with a special anti vibration varnish. Also the chassis of all Inspire products is non-ferrous aluminum."
FWIW, the transformers are 'EI' cores, and all EI cores should be constructed as described above and usually are (often are what is called 'double dipped' in the varnish, which is very helpful in the anti-vibration department). The chassis material will not affect whether a transformer makes noise or not.
Atmosphere is there any reason why manufacturers don't use nyloc nuts to mount these transformers. They wouldn't come loose with a nyloc nut.
Actually they could come loose, since what happens here is that with a enough heating and cooling cycles the varnish can relax a bit. So this might require tightening the end bells down so they don't rattle. Transformers have been made for over 100 years without the need for locking nuts.

atmasphere's avatar
atmasphere
12,104 posts
 
@mrdecibel  We had some very large EI core transformers on our MA-2 amplifier. One of them made a bit of humming. That was fixed by isomeric mounting; after that it was dead silent. The trick is not allowing the transformer or its mounting hardware to contact the chassis directly; that appears to be really difficult to pull off with this particular mounting system.
atmasphere's avatar
atmasphere
12,104 posts
 
@listening99  It would be a good idea to check in with Mr. Had and see if he has any comments. From the outside the amp looks conventional construction. Remove all the tubes before you turn the amp over to prevent damage. Keep in mind though that you are on your own here- if this is at all intimidating, it might be best to bring it to a technician to do the work.
atmasphere's avatar
atmasphere
12,104 posts
 
@jea48 A rectifier tube will not cause a power transformer to rattle (humm).


@mrdecibel  If you look at the way this transformer is mounted, using isomerics to secure it is unlikely! Its mounted through a cutout that barely accommodates the transformer core. This type of mounting leaves very little room for using grommets to isolate the chassis from vibration.


IMO/IME tightening the transformer bolts is the best option. If it does not work, replacing the transformer is the next option after that.
atmasphere's avatar
atmasphere
12,104 posts
 
I see the four screws from the top, so they are accessible from above the amp. Why remove the bottom panel?
If the screws are loose, the nuts on the bottom might spin when you try to tighten them up.
atmasphere's avatar
atmasphere
12,104 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.
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