2. amps-preamps
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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
ping2357 OP
10 posts
 
Samtse, I am using First Sound Presence Deluxe 4.0 Mk II. I am hoping to upgrade their higher end 3 box preamp.
ckoffend
684 posts
 
Back to the OP Question about the hum. I once had a large amp, big transformer, large caps, etc. . . That's a lot of reserve to energize. I know this Q is old.

But I would occassionally run into a similar problem, turns out during the hottest summer days. Called the amp mfg. thinking it was a cap or transformer. Discussed several times and eventually concluded it was a combination of a lack of power supply in my house and the very hot and humid summer days - causing everybody in town to run their ACs. Lot's of draw which seemed to result in the power reserves having a tough time staying or getting fully charged up.

Power usage in neighborhoods is up in the mornings - curling irons, coffee pots, hot water heaters, hair dryers - all energy consuming devices. Perhaps a correlation?
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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