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
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.
Steve may just walk you through a diagnostic process to discover the real issue.  Good luck.
Call, you will talk with Patrick or Steve himself. amazing people.

best of luck. keep us informed as to what happens!  cheers.
I talked to Steve.  I'm amazed a guy like that just answers the phone!  He had some suggestions around my system that is quite complicated.  He said it might be blown fuses.  Anyway, I checked, the fuses are fine.  My tech suggested getting rca to xlr cables.  I got a specific kind he recommended, something to do with pins that I didn't follow.  Anyway, long and short, using rcas is catastrophically noisy, using the xlr inputs with xlr to rca cables and the amp is up and running and sounding great.