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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
7 responses Add your response
west99 OP
13 posts
 
Thanks guys, I appreciate your input (no pun intended).

I'll make sure I don't connect both sets of inputs simultaneously.

I have a Mark Levinson 38 preamp in a second system that I don't use much -- I'm thinking of connecting both the Supratek preamp and the home theater processor to it, via their respective RCA and XLR interconnects, and the output of the Levinson to the Krell amp. That way I'm using the Levinson as a switch, and I can make use of it's surround processor pass-through input as well.

I'll have to try it to see if I can live with the (probably very small) sonic penalty of inserting it into the signal path -- I'm sure it will be transparent enough for watching movies at least.

Thanks again,
Kyle
kr4's avatar
kr4
3,677 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
atmasphere's avatar
atmasphere
11,793 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.
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.
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.
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!
kr4's avatar
kr4
3,677 posts
 
No. The shorting pin shunts one side of the balanced input, converting (crudely) the input stage to single-ended. Consequently, I doubt (without actual experience) that you can connect both at the same time.

But I would consult Krell.

Kal
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