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Transformer hum with AC fluctuations

I was about to buy an isolation transformer (Tripp Lite) in hopes of cleaning up my inexpensive CDP's sound a bit (Tobias's rec on the cables forum), and now I've run into another AC-related problem.

I live in an old, small rural town in PA, and this time of year power demands start overwhelming our grid: our lights dim for brief moments (a second or so) and then come back to normal all evening long. Coinciding with that--and only at high-usage times on the grid--the transformer of my NAD C325BEE has started making a hum that's audible from across the room. The trannie has always hummed faintly (had to put my ear above the amp to hear), but now it's hard being in the room with it. It doesn't come through the speakers or headphones.

I have two questions: is an isolation transformer likely to hum just as much as my NAD's transformer? and is there a better route to cleaning up my AC (the kicker: within a $200 budget)? I appreciate any other suggestions/solutions. Thanks in advance.
ablang
johnmcalpin
58 posts
 
It certainly is odd. I figured the Equitech would take care of it, but it's still there. But, and more frustratingly odd, is that it is intermittent. It's a head scratcher.

I also have the amp -- and every other component -- sitting on a Sistrum platform. I wonder if setting it on something else might do the trick.

Don't get me wrong, this amp is amazing and in the grand scheme of my system the hum is a very minor flaw. And while I go through all sorts of system do-over fantasies -- like the one I'm in now -- I know the Zeus is a keeper.
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swampwalker's avatar
swampwalker
5,138 posts
 
Since it varies in time and intensity, I would have to guess that it is something coming in on the AC, but using an isolation transformer would seem to rule that out. Some units seem to be prone to transformer hum, like my old Moscode. If the hum is exacerbated, I would guess that the transformer hum, which I am pretty sure is a mechanical issue/resonance is exciting a resonance in the platform it is sitting on, if that makes it worse. I would try a diff platform to see if that helps. I also think that it is possible that a stick on vibration damper (is it dynamat?) might help. Also tightening the xformer hold downs. Or maybe loosening them and putting a elastic washer btwn fastner and xformer.
johnmcalpin
58 posts
 
When I first got the amp it sat on a Polycrystal stand for a month or so. I might go back to something like that, or a maple block. Sistrum has been awesome for the speakers and other components. Time to experiment.

Swampwalker, you've got some very sound tips. I kicked around the idea of losening the nuts the other night while I was biasing the tubes.
johnmcalpin
58 posts
 
So I spent part of yesterday thinking I needed a new amp stand and searched out the Symposium and others and decided to make a switch after Christmas.

And then last night not a peep out of those transformers whatsoever.

Talk about audio nervosa!
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