This just came out in Part 3 of the Bill Klause article that Rustydoglim referred to in this thread, I think it is of interest to Nuforce/Nuprime owners
"The Amplifiers
As I stated in Part 1 of this article, over the past 25 years I have experimented with a variety of amplifiers – everything from solid state, OTL, push-pull designs and single-ended designs. Over the last decade, my reference design was a 50-watt, push/pull pair of 300B mono blocks. My ears were used to the sweet velvety mid-range with a roll off in both the high frequencies and the bass. It was a good compromise in an audio room that was by and large untreated.
On my way to owning my current speakers, I picked up a pair of rather abused Tannoy Ardens. They too have a coincident design with a 15-inch woofer. I completely rebuilt and refinished them and was surprised how musical and coherent they sounded. Naturally there were some issues with cabinet resonances and their ancient crossover design. Given the 15-inch woofer, I thought a solid-state amplifier might prove beneficial with its high damping value (high current to control the movement of the woofer). A close friend, who had a 500-watt Class D amplifier, suggested I compare it against my 300B mono blocks. My 300B amps cost six times the price of this Class D amp. For my part, I expected a resounding tube amp victory over the solid-state design.
Instead, to my complete amazement there ended up being no comparison. The Class D amp was very smooth in the high frequencies, yet its mid-range had greater detail and delicacy. The bass was impactful and well delineated and better extended. Yes, the digital switching amp, with its damping factor over 1000, was more capable of controlling the woofer than a 300B amp, with a damping factor of about six. The inability of the 300B amp to control the woofer created a number of artifacts that obscured mid-range details and bloated bass frequencies.
After my room was built I eventually tried the NuForce* Reference 20 mono blocks. It is without doubt the most musical, detailed and impactful amplifier I have ever listened to. Its performance is absolutely statement level. Its control over the Tannoy woofer is astounding and I’ve yet to hear a better combination of speaker and amplifier. I’ve listened to countless amps these last 20 years and this one is simply the crème de la crème of amplifiers. But this shouldn’t have surprised me. A growing number of audio hobbyists and magazine reviewers had declared that its predecessor, the NuForce Reference 18, was a statement product and you should have a listen if you were interested in a true reference amplifier. For once I had to agree with the audio press, as confirmed by my own extended listening.
A highly-regarded tube amp/preamp manufacturer, and the maker of equipment that had seen much positive press from The Absolute Sound, came by for a listen. His first response was, “Are you trying to put me out of business?” “Class D amps have finally arrived,” I replied, with a smile. I think his comment was really an acknowledgment of my well-designed listening room.
Lesson: Class D amp technology has matured over the last decade, so you have to consider it. It offers incredible power, great musicality, and runs completely cool. It seems to offer the best attributes of solid state and tube technologies without any of the drawbacks. Several amp manufacturers are now moving into the design and production of these amplifiers."