Audio-Technica AT-15S
Audio-Technica's "almost best" CD-4 pickup. It is the working-class sibling of the hand-picked AT20SL, and one of the few cartridges of its era that played both discrete four-channel and plain stereo without apology.
Overview
The AT-15S is a moving-magnet phono cartridge built on Audio-Technica's Dual Magnet principle. Two independent permanent magnets sit at 45-degree angles, perpendicular to the two groove walls, and each one generates the signal for one channel. That design is why the cartridge exists. It let Audio-Technica push response out to 45,000 Hz and beyond, into the ultrasonic range that CD-4 discrete four-channel records demanded. The Shibata stylus, a nude diamond cut in the multifaceted profile, was the other half of the job. Audio-Technica fitted it across its discrete-ready line. The company's own advertising was blunt about it: the Shibata tip was the only phono stylus designed for the new discrete four-channel records, and it went on the AT12S, AT14S, AT15S, and AT20SL alike.
What separates the AT-15S from the flagship AT20SL is selection, not design. Construction is identical between the two. The top-of-the-line cartridge is literally hand-picked from the AT-15S production run, chosen for the flattest possible response out to 50 kHz. So an AT-15S is, functionally, an AT20SL that didn't quite make the cut. That sounds like a demotion until you look at what the "reject" actually does.
The numbers, as measured in period testing, are serious. Frequency response runs flat from 50 Hz to 8 kHz within ±2 dB, then climbs gently: +2 dB around 15 kHz, +1 dB at 20 kHz, +1 dB at 30 kHz, easing to -2 dB at 40 kHz and -5 dB at 50 kHz. Separation averages 20 dB from 50 Hz to 10 kHz, narrowing to 16 dB at 12 kHz and 12 dB at 20 kHz. Output is 0.83 mV per centimeter per second, DC resistance 445 ohms, inductance 408 mH, weight 8.52 grams. Intermodulation distortion measured 2.6% lateral and 2.4% vertical, crosstalk -24 dB, channel balance within 0.5 dB. Trackability came in at 30 cm/sec on the high-frequency pulsed test (10.8 kHz), 25 cm/sec mid-band, and 19 cm/sec low-frequency. The original price was $100.00.
The trackability figures are the ones that count if you play records rather than read spec sheets. A cartridge that holds 30 cm/sec on pulsed high frequencies is handling the work that most budget moving-magnets hand back as mistracking on loud passages and inner grooves.
The same period testing documented a practical wrinkle. Duplicating Audio-Technica's published response required reducing lead capacitance considerably. The CD-4 demodulator input was specified at 100k ohms rather than the usual 47,000, and the leads from cartridge to demodulator were described as "large, fat cables." With a standard 300-pF connecting cable the response diverged noticeably. A pair of three-foot RG-58/U leads totaling 105 pF got within 2 dB of the published curve at 50 kHz. So this cartridge is sensitive to capacitance, and a careless setup will punish it. It was designed for flat response into a standard 47,000-ohm impedance in the audible band, but the ultrasonic extension that makes it a CD-4 cartridge depends on the cabling.
High Fidelity (December 1974, p.53) covered the AT-15S's near-twin under the memorable headline "Audio-Technica's 'Almost Best' Pickup," reporting a high-frequency resonance at about 45 kHz and square-wave curves showing no significant ringing — the kind of clean ultrasonic behavior that separates a real CD-4 design from a stereo cartridge with a fancy stylus bolted on.
The AT-15S sits in an odd spot among collectors. It's not the flagship, so it doesn't command flagship money, but it shares the flagship's construction and most of its performance. Original price was $100, real money in 1974, roughly the cost of a decent receiver. Today it suits someone who wants genuine CD-4 capability without paying AT20SL prices, or who wants a well-built moving-magnet with excellent transient response and a Shibata tip that treats older records kindly. The nude diamond Shibata profile was promoted for lower record wear while improving high-frequency tracing. That's a marketing claim, but a plausible one given the geometry.
The caveats are the usual ones for a cartridge of this vintage. Stylus condition is everything and can't be judged from a photograph, and a worn Shibata tip is an expensive problem. The capacitance sensitivity means it rewards careful matching and punishes whatever cable happens to be in the box. The 8.52-gram weight is on the heavy side for some tonearms, so check effective mass matching before buying. None of that is disqualifying. It's just the homework that comes with a fifty-year-old moving-magnet.
The AT-15S is a second-tier product built on a first-tier platform. Audio-Technica sorted the production run and let the best examples become AT20SLs. The ones that remained are still Dual Magnet cartridges with Shibata tips and measured performance that embarrassed plenty of more expensive competition.
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