Sharp SM-SX100 digital integrated amplifier Page 3

In such a circuit, the voltage rails apparently tend to droop below ±32V if there is an accumulation of either 1s or 0s. So the Sharp design uses a feedback loop between the power-switching circuit's output and the input of the delta-sigma chip. This adjusts the value of the data to compensate for any voltage drop in the output signal.

The output of the amplifier at this point is still a ±32V pulse train, which, if fed directly to the loudspeakers, will results in high levels of RFI. The MOSFET stage is therefore followed by an initially gradual-sloped passive low-pass filter. While this filter's passband can theoretically be half the sampling frequency, or 1.41MHz (as 44.1kHz-sampled PCM's is 22.05kHz), in actuality a 100kHz passband is chosen as sufficient to reproduce any sound, musical or otherwise, while minimizing the switching noise. The filter's output then drives the loudspeakers directly. And that's it!

The Glory!
So you have a compact, cool-running (Sharp claims one fifth the heat production of a conventional analog amplifier), energy-efficient (half the power consumption), 100Wpc amplifier with a rated frequency response of 10Hz-20kHz at full output and a bandwidth of 5Hz-100kHz, +1dB/-3dB.

Hookup was straightforward. I connected the Sonus Faber Amati Homage loudspeakers and Audio Physic Rhea subwoofer, the SACD player Sharp provided, the analog output of the Audio Research Reference phono section, set the SM-SX100's impedance switch to 4 ohms, switched the unit on...and began listening.

So how did it sound?

In a word, amazing. Even digitizing analog? Yes. There was nothing digital-sounding about the SM-SX100. If this technology sounded any different from a good analog amplifier, tube or solid-state, it was in its transient and dynamic performance. Both were both stunning, especially in the rendering of bass microdynamics.

The SM-SX100 sounded fast, but not zippy or thin. High-frequency transients—cymbals, vocal sibilants—were just where you'd want them: naturally smooth, yet exceptionally detailed and convincingly non-mechanical. Shakers, gourds, bells, plucked strings—all had breathtaking clarity and detail, and no etch.

If "digital" conjures up "ringy," "glazed," "airless," "flat," "suffocating," "confused and confusing," and the rest, forget them. They had nothing to do with this amplifier. The SM-SX100 sounded open, airy (when the source material was), and, for the most part, transparent. Playing very familiar tracks like Nat Cole's "When I Fall in Love," from DCC Compact Classics' LP reissue of Love is the Thing, I was struck by the exceptional fluidity and coherence of Cole's voice. I've heard it darker and warmer in the chest and simultaneously more etched in the vocal cords, but the Sharp's presentation was about as "apolitical" and neutral as I've heard. And his voice, while oversized due to the mix, was presented in as solidly three-dimensional a picture as I've heard it. There are a few extremely deep microphone pops on the track; the Sharp's portrayal of them was about as convincing as I've heard that familiar studio glitch.

Massed strings? Solo violin? Female vocals? With these, the SM-SX100 was fast and delicate, rhythmically lithe, and harmonically proper and convincing—but don't expect the bloom and delicacy of a top-shelf tube unit. The effortless extension will sound too bright for some ears, though I doubt anyone will come up with "hard" as an adjective to describe the amp's high-frequency performance.

But, as I found out when I played Classic Records' LP reissue and an original of Jascha Heifetz's RCA Living Stereo recording of Bruch's Scottish Fantasy, the SM-SX100 did an outstanding job of reproducing the grit of bow on strings, and rendered the silky upper register with impressive subtlety. It never sounded harsh, grainy, or brittle, though the effortless top-end extension let me know what was happening with the recording and associated equipment.

Two of the Sharp's most impressive qualities were its image solidity and three-dimensionality, probably due to its pitch-black backgrounds and sure-handed portrayal of low-level bass dynamics, and its remarkable overall bass performance. And, of course, with the quiet and bass extension, you can be sure the amp's soundstage delivery is as big and deep as the recording allows. Live recordings, like Premonition/Blue Note's new 180gm vinyl edition of Patricia Barber's Companion, were presented with all of the air and space you'd want, and the image focus and solidity that give that sense of "thereness" in your listening room.