Audio Research amps - balanced & non

...And the one big disadvantage of a transformer is phase shift and frequency roll off at the extremes. If the transformer is feeding a poorly designed wide bandwidth circuit then in fact the transformer might actually improve the sound over all. And I do agree, an active circuit is more complicated. But I think you missed my point. The point is that basically to each his own. You can't say you don't like something until you have tried it and it fails in that particular application.

Hifigeek1...Before suggesting that Jensen signal transformers exhibit frequency roll off you really ought to check the specs. I know that high power audio output transformers exhibit roll off (usually corrected by ultralinear feedback) but these low level transformers are a different kettle of fish.

If you comment further, please report the specs you find.

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.

Thank you all for your considered responses and suggestions.
Another option, of course, would be to replace the D-115 altogether with an SP-10-compatible amp such as VT 200SE or VM 220's that have singe-ended inputs (as it happens, each of these have both balanced/xlr and RCA inputs).

On that thread, I know the Ref 300 Mk II has balanced inputs only, but does the original Ref 300?
Any other Amp suggestions given I need 200wpc plus to feed MG 20.1's from an SP-10 and both phono & line/cd inputs?

Thanks!