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In the 1990s, while putting together one of my early hi-fi systems, I'd often visit New York City audio retailer Sound by Singer to gawk at their top-tier wares. On one such visit I noticed a serious-looking gentleman listening to Stravinsky's The Rite of Spring through a pair of Audio Physic's Step loudspeakers (accompanying electronics long forgotten). Sitting on their dedicated, minimalist-looking metal stands, the pint-size Steps were angled up 22° or so, to create a physical time alignment of the tweeter's and midrange-woofer's wavefronts. The Step looked odd—kind of scrawny. But these petite minimonitors projected music that seemed to exist entirely free of their cabinets, pulling off a sort of "disappearing" act I'd never before heard.

In the late 1980s, when I began reviewing high-end subwoofers, they were big and heavy, difficult to move or find space for in a room. Their controls were always on an inconveniently positioned rear panel, and there were no built-in automatic room-optimization options or parametric equalizers. Velodyne's 105-lb, downfiring ULD-18 ($2570), ca 1989, was typical: Two people were needed to unpack and move it; it was powered by an outboard 400W amplifier, connected inconveniently with a speaker cable and an RCA-terminated interconnect for its servo control; and its controls were on the bottom of the cabinet. Changing its crossover frequency involved soldering new resistors onto a printed circuit board inside the amp.

To audio designers in Japan and elsewhere, the single-ended, 300B-tubed amplifier is like a haiku: an art form defined by both its prescribed limitations and the potential such restraint offers for artistic expression. Here, the only hard-and-fast rule is a simple one: output devices are limited to one 300B directly heated triode tube per channel. From there, it's a blank slate: Do you want AC or DC on the output-tube heaters? Tube or solid-state rectification? Low or high gain? Fixed or cathode bias? New parts, vintage parts, or a mix of both? Triode or pentode tubes as drivers? Capacitors or transformers—or nothing at all—between the plates of the driver tubes and the grids of the output tubes?