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