Sharp SM-SX100 Stereo Power Amplifier 
Home Theater Power Amplifiers Stereo Amplifiers
Written by Kim Wilson   
Monday, 01 May 2000

A fact of life in the high-end world is that amplifiers are heavy, obtrusive square chassis with massive heat sinks. However, that is about to change with the release of Sharp’s SM-SX100 1-bit amplifier. The stylish silver chassis with colored accents looks more like an executive shelf component than the 100-watt 2 channel, $15,000 amplifier that delivers clean, unaltered sound, bringing digital technology to what was once a purely analog product.

The SM-SX100 is rated with an amazing frequency response of 5 – 100 kHz. Okay, we mere humans can’t hear much above 18 kHz (if we’re lucky), but the extended range ensures a flat response throughout the audible range and a reproduction range commonly associated with analog signals. It is capable of driving a speaker with an 18-inch woofer, yielding devastating subsonic frequencies, while driving the tweeter and midrange effortlessly. Dynamic range is measured at 105 dB, though the theoretical dynamic range associated with this technology could attain an outstanding120 dB.

The SM-SX100 supports every conceivable digital input, including both ST and Toslink optical inputs, plus BNC and RCA coaxial inputs. There are also RCA and XLR analog inputs. Additionally, there is a dedicated SACD (Super Audio CD) one-bit signal input for direct connection to Sharp’s upcoming DX-SX1 SACD Player. The exclusive 13-pin cable connection will provide the first direct bitstream coupling of a SACD signal with a one-bit amp. Only Toslink and RCA analog outputs are provided. The RCA outputs only pass signals from the RCA analog inputs, not the digital inputs. The special safety RCA jacks allow for plugging and unplugging cables while the amplifier is powered up. The double-pole speaker terminals are insulated, with two sets per channel facilitating bi-wiring.

To minimize interference, the internal structure has a two-piece construction, separating the power supply and one-bit sections from the control section. The slim SM-SX100 (18-19/32" x 3-1/2" x 18-3/16") fits in any rack and never gets hotter than the average audio component. In fact, it generates 80 percent less heat than your average analog amplifier. Separating the amp or providing extra ventilation shouldn’t be required. Weighing in at about 40 pounds, it’s not exactly a lightweight, but it’s far more manageable than the average high-powered amplifier. I had a unit with Peacock Green accents, but the U.S. version is only available with black accent side pieces.

The original digital vs. analog controversy during the advent of CDs wasn’t just started by some old-timers who couldn’t accept the digital age. There was serious validity to their argument.

Vinyl has and still has twice the reproduction range (40kHz) of CDs (20kHz). This accounts for the palpable sense of depth and reverberation on vinyl that is often missing from CDs. However, the improved dynamic range, particularly in the high frequency range, accounted for the immediate popularity of CDs, as they just sounded louder.

Therefore, the digital engineering challenge has always been to get the same reproduction range that analog signals have, while preserving the key advantages of digital signals, which are lack of distortion, significantly less noise and no signal degradation. In 1995, Sharp proposed the one-bit theory at the Advanced Digital Audio (ADA) conference of the Japan Audio Association. At CES 2000, they demonstrated the SM-SX100, the one-bit amplifier for the new century, ushering in a whole new approach to signal amplification.

Attaining a sampling frequency 64 times faster than a CD, the SM-SX100 dramatically increases the sampling frequency to 2.8224 MHz (2,822,400 times per sec) and shifts quantization noise to the high-frequency spectrum using a seventh order sigma-delta modulation code. A one-bit signal is produced every 0.3543 ms. These one-bit signals represent amplitude with the usual 1 or 0 binary signature. The signal travels through a low pass filter to become an analog signal that is then transmitted to a high-speed switching circuit that generates signals to drive the loudspeakers. The internal process is about half that of a conventional signal path.

Where multi-bit PCM signals record each quantized sample as an absolute value, one-bit signals record the fluctuation of the sample from the previous one, making them characteristically similar to analog signals without the negative attributes. The goal is to attain a sound that is extremely close to the original, with instantaneous response and a wide frequency range, plus lots of extra dynamic range.

So, do the theoretical and technical claims bear out sonically in a real world environment? In a word, YES! I found using the SM-SX100 to be an extraordinary and unexpected experience. The level of performance on all source material went well beyond any other amplifier I’ve had the opportunity to review or use on a long-term basis. It is one of those rare products that raises the bar so high that it is like listening to a good quality system for the first time. You'll want to hear what all your favorite recordings sound like on it.

For the main part of my evaluation, I was using Revel Performa F30 speakers. Now, before you go, "Oh, well, maybe it was just the speakers," I had originally hooked up the SM-SX100 to the Monitor Audio Silver 4s that I reviewed last month. I was knocked out of my chair. If you thought I liked the speakers before, had I reviewed them with this amp, I would have been crying. It was like listening to a completely different speaker system. The high frequency response was tighter, more robust and the dynamic range expanded twofold. I knew the Revel Performa’s were being delivered any day and my excitement level went up 110 percent.

Once I hooked up the Performas. the first thing that struck me was that I could stand directly in front of the speaker with the amplifier powered up and I heard…nothing. Right off the bat, the noise floor was next to nil. Only when I put my ear right up to the driver could I hear a very faint and distant hum.

Starting with the 20-bit recording Gravity (Narada Equinox) from neo-flamenco guitarist Jesse Cook, the tracks "Falling from Grace" and "Into the Dark" exhibited unparalleled depth with real to life reverberation. Not only are instruments three-dimensional, but every nuance of the instruments’ acoustical properties is out front, such as fingers on the guitar strings and the distinct vibration of the strings themselves. Each note is clear and articulate, even on fast arpeggios.

As I am not a big listener of classical music, I rarely listen to an entire composition. Mostly I listen to classical discs when reviewing products in order to provide a well-rounded assessment on all types of music. The perfectly pure and resonate cello from Yo-Yo Ma’s recording of "The Protecting Veil" by John Tavener (Sony) was so beautiful and soothing that I couldn’t turn it off, even after making my evaluation. The dynamic range of the first movement in this piece reached levels I’d more likely equate with a movie soundtrack.

The SM-SX100 goes beyond reproducing sound with an accurate tonal balance. What is even more remarkable is how this amplifier has the ability to convey the emotion and intensity of the music, allowing you to forget about the mechanics of sound reproduction and just enjoy the performance. That’s a real plus for me because, as a reviewer, I get all caught up in how something sounds and often forget about just sitting back and listening.

TakaDake is an Asian group that plays only percussion instruments made out of bamboo. On the 20-bit Asian Roots (Denon) CD, John Neptune Kaizan adds his bamboo flute (shakuhachi) to the mix. The tonal differences, as well as the various resonate qualities, of these bamboo instruments is about as realistic as you could ask for from a recording. The instruments are alive and vibrant. There is a very natural sense of performance space.

Inva Mulla Tchako’s extraordinary performance on the track "Lucia Di Lammermoor" from the Fifth Element movie soundtrack (Virgin) reveals a voice with exceptional clarity and presence. The dynamics of her voice are chilling and the tonal quality remains uncolored as she moves up the scale. In "The Diva Dance," her voice is altered electronically to indicate an ability to vocalize beyond human capabilities (since her character is alien, we can believe this). Each note was so transparent that the "real" notes just popped out because they had a certain resonance that could not be emulated by the flat digitized notes. While this probably detracted from the desired effect, to hear each note so sharply was breathtaking.

Janet Jackson releases some of the most rich and well-produced pop tunes of any recording artist. The SM-SX100 reveals the detailed and intricate layers off the tracks from The Velvet Rope (Virgin) with astounding precision and accuracy inside a well-defined and expansive soundfield. This amp rocks and pumps up the jam as good as any ultra-heavyweight amp of 200 watts or more. Bass response on "Go Deep" is fast and the resolution is really tight and expressive. It is as bone-rattling as a disco, without the distortion and excessive boom associated with those types of systems.

The Downside
More of an annoyance than a real defect, the amp defaults to the SACD input upon power-up. The assumption here is that the owner is buying this amp for use with the as-yet-unavailable SACD player.

Now, granted, the front panel controls are minimal, but there is no remote to adjust volume or input selection. If a preamp were used, the volume of the SM-SX100 could be preset and the preamp would control the overall volume. However, the purest performance can only be attained when there is a direct connection from the digital source device to the amp without additional components.

Any time that a product is priced out of reach of the common man (and woman), we generally point that out as a negative. However, it makes sense that this limited edition amp is so pricey. It represents a new technology and is the first of its kind. There’s always a price to pay to get in on the ground floor.

It’s pretty clear that this amp isn’t going to be flying off the shelves, no matter how impressive the sound. The real value is the promising performance from future amplifier products for various applications at a wide variety of prices. While I was told that several different types of products were in development, the only ones Sharp is talking about are the 50-watt SM-SX1 amplifier and companion DX-SX1 SACD player (which can also be couple to the SM-SX100). Both are ultra-compact and would easily fit on a shelf or desktop. The price for the combo is targeted at $7500 and scheduled to ship in July (although that could change). The DX-SX1 SACD connects to either the SM-SX100 or SM-SX1 amp for a direct bitstream coupling.

I’ve listened to a fair share of high-powered amplifiers and most have some sort of sonic characteristic that is their own, be it good or bad. The SM-SX100 adds nothing, nor takes anything away. It is just a conduit for the original recording, unaltered and unprocessed.

Call your local dealer and see if they carry the Sharp one-bit amplifier so that you can experience first-hand what will likely be the wave of the future. Digital amplifiers will ultimately replace their analog counterparts as surely as the CD player replaced turntables and DVD has replaced Laserdisc.
Manufacturer Sharp
Model SM-SX100 Stereo Power Amplifier
Reviewer Kim Wilson

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