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rca and xlr inputs connected simultaneously?

I have a Krell KSA 200S amp with both balanced and single-ended inputs. Due to long runs, I use balanced interconnects from my Krell HTS2 home theater processor's front channel outputs to the Krell amp.

I also have a Supratek phono preamp for listening to analog on 2 channels. I have single-ended interconnects between it and the Krell amp.

I have never connected both at the same time. If I'm watching a movie, I disconnect the RCA's and plug in the XLR's; if I'm listening to vinyl, I do the opposite.

I have no idea what would happen if I connected both at the same time. I can't imagine that it would damage the amp but since I don't know, I haven't tried it.

I know there are shorting pins that came with the amp which I insert into the XLR inputs when the RCA inputs are being used, but there are no RCA "shorting pins". Does that mean that if both inputs are connected, the XLR's take priority and the single-ended signal is ignored?

Any help would be greatly appreciated.

-Kyle
west99
unclejeff
1,313 posts
 
DON'T DO IT! All amps are either balanced or unbalanced with a circuit converting the alternate feed. The feedback will fry something real bad!
eldartford
4,262 posts
 
If you connect both, the (-) line of the balanced interface becomes ground, so the "balanced" interface actually becomes single-ended (regardless of using XLR conncetors).

I don't understand Kal's description of this setup as "crude". It's just not balanced.
dne
141 posts
 
I had a similar question once and consulted with a friend who had a Krell KSA 50 (I think it was). He said the Krell instruction manual said specifically NOT to do it. If you have the instruction manual, take a look. I'm assuming you are talking only about the connections, not using them at the same time (obviously).

However, I asked this question to Hafler once (for a pro 9505 Transnova amp) and they said a concurrent connection wouldn't be a problem, presumably since the Hafler amp has a switch to go from XLR to RCA, so that either one or the other is engaged but not both simultaneously.
atmasphere's avatar
atmasphere
11,834 posts
 
Unclejeff is incorrect here. Usually in a balanced amplifier the RCA corresponds to either pin one or pin three of the XLR.

The real issue is that the loading from the two sources will interfere with each other and the sound will be less than optimal (rolled off, distorted or both), although there is no risk of damage. So you will have to continue switching cables unless you can convince someone to install a switch for you.
kr4's avatar
kr4
3,685 posts
 
"I don't understand Kal's description of this setup as "crude". It's just not balanced."

Agreed. The described method simply does not make use of the other side of the balanced input and, as you know, is pretty standard. This reduces the input gain but keeps the higher input noise of the balanced input. A switch to disconnect the other side of the input stage would be more elegant although more expensive. In practice, probably little or no subjective difference.

Kal
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