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McCormack DNA 500 loud hum

So I just picked up a McCormack DNA 500 and the damn thing just hums loudly in one channel when coupled with my cyrus preamp.  I took it in and the tech said it's because the rcas aren't grounded as they enter the same Jensen transformers as the balanced connection, this can result in really bad humming.  He's going to ground them but I just can't believe that I can't run this amp stock with my cyrus preamp?  That preamp shouldn't have any problems with this amp.  Any one have detailed knowledge of these a,ps that can guide me or my technician?

malthuse
randy-11
1,913 posts
 
could be the electrolytic caps - see if he mentions that
gdnrbob
4,444 posts
 
I would not doubt Steve and Patrick's knowledge about amp construction-no disrespect to your tech, but they are the most 'stand-up' guys in the business. Call SMc and get the answer from the horse's (designer's) mouth.
B
malthuse OP
18 posts
 
It not the caps, that would just make a mild hum and they all look in good condition.  An amp this old is unlikely to have cap problems.  This is a loud open circuit sound, like if you (very stupidly) remove one rca while the amp is on, like I've done on other amps on occasion.  I was worried for my speakers it was that loud.
malthuse OP
18 posts
 
I'll contact McCormack.
hifiman5's avatar
hifiman5
1,832 posts
 
Steve may just walk you through a diagnostic process to discover the real issue.  Good luck.
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