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Gamut M250 MK3

I got a pair of Gamut M250 Mk3 mono-blocks that went in place of a D200 mk3. They were installed yesterday, and worked fine for a day. This morning I turned on the amps to warm up. A bit later I went back to the listening room and heard a very loud hum. First I looked out the window for a garbage truck; then put my ears against the speakers. Nothing there. It was coming from the amps. Power-cycle of both amps confirmed that both were making that noise, though one was louder than the other. About 10 minutes later the noise was gone. I have a feeling that this might be one of those intermittent problems that's difficult to track down, but I do want to get to the bottom of it while they're in warranty. To other owners of the M250, have you ever experience such a problem?
ping2357

Showing 1 response by musiklab

musiklab
2 posts
 
When the mains power waveform is distorted ( sine wave with flattened top) from heavy loading in the local grid, any transformer will hum.
It is called magnetostriction, the iron core actually changes shape, vibrating internally. Warming up may reduce the noise.

well designed toroid transformers for Audio use have about 5% magnetic headroom. The ring shaped core is wound from a long band of grain oriented silicon steel, and cast in epoxy to prevent buzz. The finished toroid xformers are also vacuum impregnated and baked to prevent loose windings buzzing.
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