"Musical Fidelity X-10D" it said on the box. No, this is not bathtub mildew remover or laundry detergent. Actually, it's hard to figure out exactly what it is. The box is little help. Musical Fidelity calls the X-10D "the missing link," a "pure Class A CD-player accessory."
Lee de Forest filed for a US patent on his "Audion"—the first triode—on October 25, 1906, but never could explain why it worked (footnote 1). It was up to Armstrong and Langmuir, in their pioneering work, to place the hard-vacuum triode on firm scientific ground. When the US entered World War I in April 1917, the Army had to rely on French tubes. Six months later, Western Electric was mass-producing the VT-1 receiving tube and the VT-2 transmitting tube. However, it was only in the decade following World War I, as designers became conversant with the triode amplifier, that many of the crucial elements of tube amplification were nailed down. Technical issues such as coupling two gain stages and selection of optimal coupling impedance were already resolved by the mid-1920s. The triode ruled supreme until the tetrode came along in 1926, followed in 1929 by the pentode from Philips's research laboratories in Holland.
Over the past two and a half years, I've auditioned and reviewed a number of digital audio products. It has been a fascinating experience both to watch digital playback technology evolve and to listen to the results of various design philosophies. The road to more musical digital audio has been a slow and steady climb, with occasional jumps forward made possible by new techniques and technologies. Making this odyssey even more interesting (and confounding), digital processors seem to offer varying interpretations of the music rather than striving toward a common ideal of presenting what's on the disc without editorial interjection.
To high-end audiophiles, the Boulder 500 amplifier and its less expensive derivative, the 500AE (Audiophile Edition), would not seem to be "high-end" designs. They are designed around op-amps (felt by many to be generally poor-sounding), they have scads of negative feedback (which is perhaps why op-amps sound bad), and they have only a moderately hefty power supply. Why, then, is Stereophile publishing a review of an op-amp–based power amplifier? Read on...
I still have fond memories of my first Krell amplifier, a KSA-50. Back in those days (date purposely omitted), my principal source of audio equipment reviews, aside from Stereophile and The Absolute Sound, was Hi-Fi News & Record Review, which I read voraciously from cover to cover every month. One fateful day while sitting by our community swimming pool, I happened upon an enlightening review of the KSA-50 written by none other than our own John Atkinson, editor of HFN/RRat the time. His words describing "the steamroller-like inevitability of the bass with this amplifier" haunted me for weeks, until I got up the nerve to audition, and ultimately purchase, my first Krell product.
In the Fall of 1989, Stereophile magazine released its first recording, of Gary Woodward and Brooks Smith playing flute sonatas by Prokofiev and Reinecke, and a work by American composer Griffes that gave the LP its title: Poem (footnote 1). The full story was published in the September 1989 issue (p.66). We wanted to offer our readers an LP of acoustic music made with the minimum of electronics and processing—the sounds of the instruments would be as true to reality as possible. The images of the instruments were also captured with a purist microphone technique so that, with even a halfway decent system, a true soundstage would be created between and behind the loudspeakers when the recording was played back.
Loudspeaker designers are dreamers. Something takes hold of a manthe fact that loudspeaker designers are all men must be significantand he wrestles with recalcitrant wood, arcane drive-units, and sundry coils, capacitors, and cables, to produce something which will be individual in its sound quality yet inherently more true to the original sound. An impossible task. Yet if there were to be an aristocratic subset of those dreamers, it would be those who have taken upon themselves the burden of producing electrostatic loudspeakers. For these farsighted engineers, there is no standing on the shoulders of others, there is no recourse to tried and tested combinations of other manufacturers' drive-units. Every aspect of the design, no matter how apparently insignificant, has to be created afresh from first principles. For a new electrostatic design to produce a sound at all represents a great triumph for its progenitor, let alone having it sound musical. And to produce an electrostatic loudspeaker that is also possessed of great visual beauty is indeed a bonus.