Historical

The quest for a full-range electrostatic loudspeaker has occupied many engineers' minds for many years. The problems are manifold: large physical size (which can lead to room placement problems and poor dispersion), the difficulty of achieving high sound pressure levels, the need for a potentially sound-degrading step-up transformer, and the unsuitability for production-line manufacture. Even so, the potential rewards are so great that one can understand why loudspeaker designers keep on attempting the apparently impossible. Epoch-making models do appear at infrequent intervals, keeping the flame burning since the appearance of the original Quad in 1955: Acoustat, Sound Lab, and Beveridge in the US, Stax in Japan, Audiostatic in Holland, Quad, of course, in England, and now MartinLogan.

"Why do rhythms and melodies, which are composed of sound, resemble the feelings; while this is not the case for tastes, colors, or smells?"---Aristotle

The $395 NAIT, rated at 20Wpc, is a good-sounding little amp. It's very open and spacious-sounding, but, like the $250 Rotel RA-820BX, sometimes sounds a little hard in the upper registers.

We have still not received a pair of these for formal testing, which may be a good thing in view of our feelings these days about "updatings." (Our feelings about such are clarified in this issue's "As We See It.")

Editor's Note: One-bit DAC chips in the 21st century, where the analog output signal is reconstructed from a very high-rate stream of pulses, are ubiquitous. But a quarter-century ago, those chips were only just beginning to stream from the chip foundries. In this feature, we aggregate Stereophile's 1989 coverage of the then-new technology, starting with Peter van Willenswaard on the basics.—John Atkinson.

1989 may well become the year of the D/A converter (DAC). CD-player manufacturers have, almost without exception, launched research projects focusing on this problem area of digital audio; many of these projects are already a year old. This is, however, by no means the only imperfection keeping us away from the high-quality sound we have come to suspect is possible with digital audio media, and maybe not even the most important.

This is something we don't see too often: an entirely new approach to power amplifier design. As Quad points out in its literature for the 405, class-A operation of transistors provides the lowest distortion, but drastically limits the amount of power an output transistor can deliver without overheating. (Most transistor amps use class-AB output operation, in which each of a pair of power transistors handles part of each signal cycle and shuts down during the other part. Imperfect synchronism between the two halves causes the familiar "crossover distortion," which accounts for most solid-state sound. In class-A operation, each output transistor draws current though the entirety of each signal cycle, eliminating the crossover transition but doubling the amount of time current is drawn, and thus tending to cause the transistor to heat up more.)