I ended up purchasing the ARC SD135 amplifier that was for sale here. I received it today via UPS. I installed it in my system after work, and I have been listening to it these last few hours. The first thing I noticed when I cued up a 1970s UK pressing of Yes' 'Fragile' LP was that I needed to turn the volume up to 12:00 compared to 9:00 with my DNA-125. The second thing I noticed was how much more fleshed out everything sounded compared to the DNA-125. Bass notes were more pronounced and imaging was much more lush, now being three dimensional. The DNA-125 was "almost there," while with the SD135, I am there. Something is definitely to be said for brand synergy. It almost seems like Audio Research had users of their classic tube gear in mind when they designed the SD-135. While the DNA-125 is a brilliant amplifier, the ARC SD135 is another league altogether. I have not noticed such a huge improvement in the sound of my system since I started cleaning my records with a record cleaning machine instead of hand washing them.
My music sounds so wonderful that I cannot stop listening to it. In successive order I have played Pink Floyd's 'Dark Side of the Moon' SACD, an original UK LP pressing of Spring's self-titled album on RCA, the first side of an original UK LP pressing of ELP's 'Tarkus,' and I am now listening to an early UK LP pressing of John McLaughlin's 'Extrapolation' on Polydor. This is what enjoying music is all about. If the wife didn't want to go out to dinner tonight, I would almost be tempted to listen to every album in my progressive rock collection.
In case future web searchers view this thread years down the road, if you are lookiamplifier outstanding amplifier which has low gain to pair with your high gain tube preamp, look no further than the 130 watt/channel SD135. It is a real sleeper and an absolute gem in the ARC line-up.
One other great thing that didn't happen when I powered up the SD135 was the absence of the somewhat loud thump I would hear when I turned on the McCormack DNA-125. This occured even when I let my SP8 warm up for 20 minutes. I have been told that this was caused by DC voltage. The SD135 has a sophisticated, non-fused sensing circuit to protect it and your loudspeakers from DC at the output. The SD135 starts up slowly with a two second warm-up cycle. Hence there are no thumps. The SD135 is heartily recommended.
