XLR or single ended cables and why?

Simple answer: With your Krell gear, you should definitely try out a balanced connection (and this is regardless of how long your cable run is). You don't need to commit first to purchasing the XLR interconnects if you can borrow a pair from a friend or a store demo for audition. Of course it would be ideal if you could either get ahold of a pair that corresponds to your usual reference single-ended IC's, or else wrangle pairs of the same audition model in both XLR and RCA versions so that the comparison isn't confounded by uncontrolled variables. Then just listen, not for noise per se, but for probably somewhat subtle (which is not to say unimportant) musical differences, especially concerning transient, dynamic, spatial, tone color saturation, and transparency/resolution qualities. Remember that because a balanced connection will usually yield a higher volume than single-ended (typically about 6dB hotter), for valid results always compensate with the volume control to equalize levels when performing A/B comparisons.

In my limited experience, I tend to agree with balanced cables for balanced electronics. Krell states that both components you have are balanced. Nothing to get excited or impatient about. Mortgage or rent, food, beer, and some good CD's come first.

Ghostrider45,

You are right that I have oversimplified.

RCA uses ground to carry half of the signal whilst XLR uses an additional wire. Signal levels are different as well. Circuits are designed differently too. Using the chassis for carrying part of the signal (RCA) does run an increased risk of picking up noise. A larger signal (balanced) with shielded cables (XLR) will be relatively more immune to noise.

But all this is really splitting hairs when considering most domestic applications. Many consumer grade equipment manufacturers offer only RCA connections and for good reasons; the majority find these circuit designs/connections perfectly acceptable.

Technical reasons only - don't read this if you have a headache...

You have to consider the signal transfer through the cables and also the quality of the circuits on both ends.
Balanced circuits are more complicated, so more things can "go wrong" with them. If you go by the motto "the simpler - the better" then you'd probably prefer single-ended circuitry. There is a reason why SET amps are popular...

Now for the cables themselves. On a technical basis, cables have two signal wires in opposite phase. Logically, it is best to arrange these two wires in a balanced geometry (even for RCA cables) **AND** equalize the magnitude of the currents flowing in them. The electromagnetic fields of the two wires will cancel each other, so you get the least leakage (i.e. noise) from this cable. In addition, the geometrical balance will reject externally-induced noise.
Balanced circuits almost always guaranty the above condition for the equal magnitude of currents. Single-ended circuits do not always adhere to that. The reason is that the single-ended stereo (or multi-channel) circuits usually **SHARE** a common ground. The currents generated by the Left channel driver **CAN** flow in any ground wire in any interconnect, since they are all shared electrically, and have roughly the same resistance.
It is a different situation if the grounds are electrically seperated. Such is the case with a true dual-mono implementations or monoblock amplifiers, if they don't share grounds with an external ground wire or through the AC ground.
Confusing? Perhaps a little bit...
Bototm line is, that for your interconnect to do a good job - you either go balanced (guaranteed "success") or pay special attention to your single-ended setup. Anything else will compromise the symmetry of current flow in your interconnect and would make them possibly the "weakest link"in your system.

Tvad wrote:

"standard rca audio interconnects use only a single "unbalanced" conductor.

This is not true. Single ended RCA terminated cables use two conductors. One positive, the other negative. The (+) carries the signal away from the source. The (-) carries the signal back towards the source. Both conductors have an equal effect on sound quality. For this reason, one should never use audio rca cables in which the (-)conductor is a braided shield.

A balanced XLR cable also carries two signals. One being in-phase, the other out of phase. A third ground wire allows the ground potential between the components to "equalize".