Audio Research amps - balanced & non

"The VT-130SE does not have a phase splitter and requires a true balanced input to operate correctly."

It will operate "correctly" but not "optimally" in conjunction with a single-ended source. With an SE source and an RCA/XLR adaptor, one phase of balanced circuitry floats unused.

BTW, VT130 is a much better amp with Infinicap or similar upgraded coupling caps.

Marty, You could be right, but the difference between balanced and unbalanced operation is more typically described in terms of loss of gain(typically 6db) and signal-to-noise ratio, due to sacrifice of common mode noise rejection inherent in balanced circuitry. I would be surprised if one single phase of VT130 used in SE mode has distortion greater than a comparable high-quality single-ended design. However, it is admittedly a waste not to utilize a fully-balanced amplifier to its full capability.

Will these problems occur with any fully balanced amp or preamp used with an XLR/RCA converter, or only ARC?

Of course there are transformers and there are transformers. Galvanic isolation is a good thing, as is balanced operation--both enabled by coupling transformers. But design & quality vary.

As if these responses are not confusing enough, I'll add my own experiences with transformer coupling. I use a LF-frequency optimized Jensen Isomax between a balanced preamp and a sub plate amp-- which does a great job. On the other hand, the Jensen step-up transformers in my original BAT VK-P10 phono stage sounded mediocre. Similarly, in another high-gain balanced phono preamp, I found Cinemag step-ups were easily surpassed by gain achieved using matched bipolar transistors. Finally, the very expensive Audio Consulting Silver Rock step-ups that I use in the analog section of a modded CDP sound superb-- discernably better than other step ups I tried in that application.

I don't think generalizations about transformers hold up across applications.