Balanced vs. Single Ended Interconnects

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My experience has been that I've noticed only a modicum of difference between XLR and RCA, though the bulk of my system is unbalanced, thus RCAs have always been the most prevalent. The most significant differences between interconnects that I've heard is in the quality level and architectural differences in the cables between brands, type of copper or copper vs. silver, gauge, connectors, and dielectrics. I'd place the connection type as a lower priority and give higher priority to the quality of cable that is a good match in your system.

I was able to borrow a pair of monoprice premium XLR cables from a friend and hooked them up yesterday.  My initial response was positive, but after a little longer listening I felt like some of the smoothness was missing.  I currently have the Audioquest Sydney RCA cables back in the system for another round of comparision.

@chrken - While it is possible that at the lengths of cables that are generally used in home audio the difference between balanced and unbalanced could be negligible, a quality balanced cable connecting two balanced components should always be superior (all other things being equal).

I tried XLR mogami vs Purist Proteus RCA (5m) from an unbalanced crossover or preamp to a fully differential amp. The Purist sounded like Purist and the XLRs sounded more distorted, which was the least surprising outcome. 

@ohlala - If you're connecting to an unbalanced component then balanced cable provides no benefit.  If it's a cable designed for an unbalanced connection that just has an XLR connector then I'd anticipate that it would perform nearly identically to a standard unbalanced cable.  If it's a cable designed for a balanced connection with an RCA connector, then I'd anticipate that it might perform poorly since it's being used in the wrong application.