Audio Dynamics ADC-25
A hundred dollars bought you a cartridge and three styli - and the idea that not every record groove wants the same diamond.
Overview
Audio Dynamics built the ADC-25 on a premise that sounds almost heretical today: the cartridge isn't the fixed variable, the record is. The ADC-25 shipped as a complete system - one induced-magnet body plus three interchangeable stylus assemblies - so the owner could match the diamond to the disc. The three styli were a 0.3 x 0.9-mil elliptical, a 0.3 x 0.7-mil elliptical, and a 0.6 conical. Each was color-coded, so you could tell them apart in a dim listening room. High Fidelity (December 1969, p.82) asked the obvious question bluntly in its equipment report - who needs three styli for one cartridge? - and answered that it depends on what records you own and how fussy you are about playing them.
The generating principle was Audio Dynamics' induced-magnet design. The company had been refining it since 1961, when it brought to market what Audio-Collection (1970, p.57) describes as the world's first commercially available high-compliance cartridge. In the ADC-25 the moving system is kept light and compliance is pushed high. The manufacturer's figure was 40 x 10⁻⁶ cm/dyne. That is why the recommended tracking force range ran from just ½ gram to 1¼ grams, a featherweight window even by later standards. It has consequences for anyone running one today.
The published numbers were ambitious. Frequency response was quoted at 10 Hz to 24,000 Hz ±2 dB. Channel separation was 30 dB from 50 Hz to 10 kHz, falling to 20 dB between 12 kHz and 24 kHz. Sensitivity was 4 mV at 5.5 cm/sec recorded velocity, vertical tracking angle was 15 degrees, and the recommended load was a nominal 47,000 ohms. That is the standard moving-magnet input, so the ADC-25 drops straight into any phono stage built for MM carts. The price was $100 suggested resale, which in 1969 was serious money for a pickup. Audio Dynamics' own advertising leaned into that, calling it "the little perfectionist" and conceding the cost was "comparatively high" while insisting the difference in reproduction was "beyond comparison." Marketing copy is not a verdict, but it shows who the cartridge was aimed at.
The ADC-25 asked two things of its owner: patience and a good arm. HiFi/Stereo Review (July 1969, p.59) noted the very high compliance and warned that the cartridge should only be used in the best of arms - low friction and low mass. That is fair counsel given how little force it needs to stay in the groove. A heavy or sticky tonearm will fight a cartridge this compliant. Get the match right and it tracks at pressures most pickups of the era couldn't touch. The same review confessed that, between the three styli, the differences were not easy to detect in listening. Perhaps with unlimited time and a hand-picked record collection they'd have surfaced.
Audio Dynamics also sold a way in for the budget-conscious. The ADC-26 was the same cartridge with a single elliptical stylus at $80, and the company pointed out that the other two styli could be added later. The replacement styli carried their own part numbers, 251 and 252 in the period spec sheets, which matters to anyone hunting parts a half-century on.
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