Audio-Technica AT-15SA
A universal phono cartridge with a quoted response of 5 Hz to 45,000 Hz, a Shibata stylus, and an individually-run curve in every box.
Overview
Audio-Technica's own advertising for the AT15Sa claimed that choosing it could add more listening pleasure per dollar than almost anything else in a hi-fi system. Anyone who has spent years swapping cartridges in headshells will raise an eyebrow at that. But the AT15Sa had specifics behind the line: a genuine nude-mounted Shibata stylus, the company's Dual Magnet generator, and a frequency response quoted from 5 to 45,000 Hz.
Audio-Technica built the AT15Sa to be a "universal" cartridge, one that could handle mono, stereo, matrix, and discrete four-channel records without compromise. That counted in the mid-1970s. CD-4 discrete quadraphonic discs demanded extended high-frequency response far beyond the audible band, and a cartridge that couldn't reach up there couldn't track the carrier signal. So the 5 to 45,000 Hz spec wasn't a vanity number. The format required it.
The Shibata stylus was the other half of the story. Audio-Technica described it as a major improvement over any elliptical stylus. The reasoning was physical: the Shibata profile presents a narrower, more line-contact shape to the groove wall. That spreads tracking force over a larger area and reduces the concentrated high pressure that stress-analysis photography showed with ellipticals. The company claimed longer record life, better performance from older and worn records, and cleaner tracing of high frequencies, particularly at the crowded inner grooves where tracking gets hardest. The worn-record gain comes from the Shibata reaching parts of the groove wall that spherical and elliptical tips likely never touched.
The stylus sat on a thin-wall tapered tube with a nude square-shank mounting. Audio-Technica claimed this reduced mass and improved precision compared with common round-shank styli, and that the result was lower distortion and smoother response.
The Dual Magnet design, protected by U.S. Patents 3,720,796 and 3,761,647, used an individual low-mass magnet for each side of the record groove. Audio-Technica leaned hard on the separation figures this produced. Everyone does well at 1 kHz, it noted, but the AT15Sa held its separation at 10 kHz and above, where, in the company's words, others fail. Hi-Fi-Stereo-Buyers (May 1978, p.75) gave that some independent support. It measured worst-case stereo separation of 26 dB at 1,000 Hz and 21 dB at 15,000 Hz, and reported frequency response within ±2 dB from 20 to 20,000 Hz with channel balance better than 1 dB. The same test panel described the sound as exceptionally "sweet" and suggested it might prove unsuitable for the distortions of acid and punk rock.
Audio-Technica shipped every AT15Sa with an individually-run response curve packed in the box, so the spec sheet wasn't a best-case average. The cartridge was aimed at listeners who wanted one piece of gear to handle every record in the collection - mono, stereo, matrix, or discrete four-channel. The company's own framing was "very possibly the last phono cartridge you'll ever need."
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