Audio Research amps - balanced & non

Martykl you are correct! When driving an ARC balanced amp with the SP-10 preamp you will find that you are unable to get symmetrical clipping out of the VT-130. At about half the rated output of the amp, one half of the waveform will indeed softly clip and you will be unable to get anymore output out of the amp period. Since the waveform is asymmetrical, i.e. both halves of the waveform are not clipping at the same point, distortion products go way up because no distortion cancellation takes place. Since the amp puts out approx. 122 Wrms across 8 ohms,( i just looked at one) you would probably get about 55 Wrms. BTW if the SP-10 has not been looked at for 10-15 yrs., there are a few filter caps in the power supply that tend to fail. Look at the end gaskets on the caps with leads that come out of each end of the body of the cap (axial caps) and look for bloating or an actual hole where the cap may be venting. I believe they are located near the power transformer just to the right as you are facing the front face plate, and then look slightly below those caps as well. Hopefully, my memory serves me right. If any of the caps look like that, it's time for service. G

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

Can't answer that as question as I don't know other manufacturers circuit topology. Even with an XLR/RCA converter
you don't have the inverting half of the balanced input so unless the input circuit can compensate for that, your not going to get proper output. This is true with ARC.

The input sensitivity of both the VT130 & VTM 200 are much different than the D115. Level matching may be an issue. Why not just buy another D115? If you need more power, a D250 maybe a better option.

The quasi-balanced interface that I suggested (using a resistor to ground for the (-) wire) gets you the noise pickup reduction benefit of balanced lines. It is appropriate for equipment which is single ended internally, and useful (instead of an RCA/XLR adapter) if the power amp has only balanced input.

If the power amp has internally balanced circuitry, and performs poorly single ended, (as appears in this case) the transformer suggested by Bob_reynolds is the way to go. To describe such a transformer as "junk" reflects ignorance.