AKG P-25MD/24
A $250 moving-magnet cartridge from a microphone company, built around a samarium-cobalt magnet and a stylus you could lose in a sneeze.
Overview
AKG built its name on microphones, and the P-25MD/24 is what the Vienna firm did when it pointed that transducer know-how at phono cartridges. It was the top of AKG's stereo cartridge series, and it priced like it: $250.00, according to the manufacturer's specifications. The design uses an "improved" induced-magnet topology and AKG's patented transversal suspension for the stylus cantilever - a rigid thin-wall tube drawn from an aluminum-magnesium-silicon alloy, chosen for low mass and low resonance.
The transducer is the interesting part. A cylindrical samarium-cobalt magnet encloses four nickel-iron alloy pole pieces, and the coils are mounted on those pole pieces. AKG's stated aim was to raise basic sensitivity while allowing a lower coil inductance. The factory numbers are 900 ohms impedance and 170 mH inductance, with a recommended load of 47 kilohms and 470 pF. The housing is molded plastic, which the maker claims is free of resonances that would color the sound. It is an electrically conductive plastic, so the body grounds itself and sheds electrostatic buildup instead of collecting it. A gold-colored arrowhead at the front marks the stylus location for cueing.
The stylus assembly gives the micro-diamond (MD) name. It is a very short-shanked, nude-mounted diamond in a shape AKG calls "Analog-6," which reads as another take on the extended-line-contact profile. The tip radii are 5 × 18 μm. Diamond mass is quoted at 0.015 mg and effective mass at under 0.4 mg. Frequency response is rated 10 to 28,000 Hz, sensitivity 0.75 mV at 1 cm/S, channel separation 30 dB at 1 kHz and 25 dB at 10 kHz, channel balance within 1 dB, and IM distortion at −6 dB a low 0.3%. Static compliance is 24 mm/N. The recommended tracking force range is 1.0 to 1.5 grams, with 1.25 grams optimum.
One quirk for anyone hunting one today is the weight. AKG's installation manual lists the cartridge at 3.5 grams, but that figure belongs to the European "/35" version. Audio (August 1982, p.68) put the U.S. "/24" on a scale and found it heavier at 4.9 grams. It also noted that the maker attributes the spec discrepancies between manual and advertising brochure to the difference between the two regional versions. Confirm which variant you're getting before assuming a tonearm will balance it.
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