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MA-2 MK II.3 has 60Hz Hum...Please Help...

Posted by Tufwheel (A) on October 23, 2005 at 12:33:00

I just received a pair of used MA-2 MKII.3 amps and they both have 60Hz hum. Even with no input and pins 1 & 3 of the balanced inputs shorted, they both have this hum. It is worse with the input switch in the high resistance position. If I have to send these to Atma-Sphere it will be about $500 for shipping. Can bad tubes alone cause this? The speakers can’t be a problem. I have initially hooked up some Acoustic Research bookshelf speakers to test the amp. When I plug in my Golden Tube Audio SEP-1 preamp the problem gets a lot worse. The GTA isn’t a good match for these amps but at least it has balanced outputs. The amps make music but there is always the hum. If I can get these amps to work I will get an MP-1 preamp and some balanced sources and be in OTL hog heaven. I know these will be some really righteous amplifiers when they are working well. Any ideas?...

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