What’s the consensus of TAS’s senior editors about whether Class D amplifiers are ready for the high end? To answer that, we recorded a conference call with Jonathan, Wayne, Neil, Chris, and me in which we sum up our listening impressions and views.
Robert Harley: I’d like to get a general idea of what each of thinks of this new technology. I’ll start by saying that my first experience with Class D, through the Cary, was not positive. It had a tremendous sense of power and dynamics, but was thick, murky, and congealed. The NuForce Reference 9 SE monoblocks amps were a big improvement, with exceptional dynamics, tremendous transparency, and very good resolution. The Kharma MP150 was another step up in performance.
With all three amplifiers, however, I heard a somewhat mechanical sound in the upper midrange and treble that was the opposite of warm, lush, and involving. The upper treble also sounded a bit rolled off, not in the sense of lacking treble energy, but the feeling of air hanging in the top octave was missing. I also thought the Cary and the NuForce had a skewed dynamic balance; the bottom end had exceptional dynamics, but the dynamic range narrowed as a function of frequency. The amplifiers sounded bass-heavy. These characteristics were significantly less audible with the Kharma than the other two, but there seemed to be a common sonic thread among all three amplifiers.
Jonathan Valin: I agree almost completely with what you just said. For me, Class D on the whole—with the exception of the Karma MP150, which is, I think, in a Class D of its own—has been a disappointment. There’s something wrong with the treble of Class D amplifiers. I don’t know exactly what’s going on, but there’s a kind of a compression of dynamics, harmonics, and spatiality in the top octaves of the Class D amplifiers I’ve heard. Top-octave piano loses some of its sparkle and brilliance. Orchestral bells end up sounding like doorbells. And air, which is quite audible on a linear amplifier like the Ref 210 or the MBL 9008 (and in life), just...vanishes.
When I was listening to The Pines of Rome with the Rowland amplifier, which has some genuine virtues in the midrange, I had the weirdest sensation I think I’ve ever had listening to a stereo system. It was almost as if I could see a horizontal line running right through the center of the MAGICO Mini tweeters. Below that line, the speaker was filled with information and fairly lively dynamics (although to me Class D amps certainly don’t sound as dynamic as you’ve just said, Robert; they actually sound rather muted). Above that line there was no information at all. It was just…empty, airless space.
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