I don't really know much about JRDG but I owned a pair of Boulder 250AE monoblocks a few yeaars back. They were built like a tank and based on the famous Jensen Op Amp. However, they always had a tinge of graniness to them that never went away, weather they were left on all the time or not. They ran very cool so I'm suspecting that they were biased in the class AB range. It seems like the driver stages developed more heat than the output devices did. Overall, my KSA-80B sounded way better as long as it was left on all the time. The old Krells will still give any modern amp a run for the money.
Am getting the parts together to build a pair of Aleph 1.2's. When completed I suspect they will be the best sounding amps I will ever own. My personal feeling is that with the advancements in high power semiconductors these days, the op amp has lost out and is no longer needed in the high end market. Simpler circuits with modern semiconductors are really hard to beat!
Mark Gulbrandsen
Salt Lake City, UT