Shure N21D (c. 1961)
A stylus, not a cartridge - and the part that made Shure's mid-line pickups worth owning.
Overview
The N21D is a tubular stylus assembly. It gets talked about more than the cartridge it fits. Shure sold it as a standalone upgrade, and its own advertising made the pitch bluntly: most of a cartridge's performance characteristics are determined by stylus design, so dropping the N21D into a lower-priced body was a cheap route to a good stereo pickup. The N21D was designed for mounting in transcription arms and in record changers, with a stated ceiling of 2.5 grams tracking force. Owners report the practical sweet spot sits lower. Shure's own copy recommended 2 grams optimum for the M7/N21D combination and warned against running it over 2½ grams.
The stylus is built around high compliance. Shure's literature lists a compliance figure of 9×10⁻⁶ cm/dyne for the M3D and M7D bodies when fitted with the N21D stylus. That is what separates this assembly from the standard-issue styli those cartridges shipped with. The payoff is tracking. The N21D lets a modest Shure body ride heavily modulated grooves without the mistracking that plagued lesser pickups of the period.
Frequency response for the N21D-equipped cartridges is quoted at 20 to 20,000 cps, ±2.5 dB, with output of 5 mV per channel and channel separation of more than 20 dB at 1000 cps. Recommended load impedance is 47,000 ohms. The M3D body carries an inductance of 365 mH and a DC resistance of 330 ohms. The M7D body measures 400 mH and 400 ohms. Both are four-terminal designs that fit standard mounting dimensions.
The N21D is not a cartridge. Collectors regularly confuse the two, and the naming doesn't help. Shure's own catalog copy moves between "N21D," "M7/N21D," and "M3/N21D" as if they were interchangeable. They aren't. The N21D is the stylus. The M3D and M7D are the bodies it drops into. Shure also sold the assembly as a factory-fitted combination. The Custom M7/N21D listed at $36.75 against $24.00 for the plain M7D. The Professional M3/N21D listed at $47.25 against $45.00 for the M3D alone. The N21D stylus by itself ran $12.50 as an upgrade for owners who already had an M3D or M7D and weren't exceeding the 2½-gram tracking limit.
The reception was strong enough that Shure reprinted it in advertising for years. High Fidelity (May 1961, p.49) described the M7/N21D as extremely smooth in both frequency response and channel separation, with high compliance and the ability to track heavily recorded grooves. It also noted that the N21D mounted the stylus of the well-known Shure Studio Dynetic pickup in the lower-priced M7D body, giving buyers a relatively inexpensive path to one of the best stereo pickups then available.
The one caution in the period coverage concerns hum. In a multi-part laboratory survey of stereo cartridges, HiFi-Stereo (November 1961, p.58) found the cartridge slightly more susceptible to induced hum than most of the units tested. The magazine did not treat it as disqualifying. It is still worth knowing if the turntable sits near a transformer or a power supply.
Shure's own advertising leaned on the "musical best-buy" framing. The N21D's midrange was called out as exceptionally clean, and the company recommended the combination specifically to listeners whose present systems sounded muddly, on the theory that the midrange is where most music actually happens. That is marketing, not measurement, but it lines up with what the independent press said about smoothness and separation.
Two other details from the period record help anyone trying to date a specimen. Shure announced the N21D tubular stylus as a new component in its revised hi-fi component brochure, offered in combination with the M3B and M7D stereo Dynetic cartridges. The stylus also turns up in period system write-ups as a normal working choice rather than a specialty item. One 1961 cover installation paired a Shure M7-N21D with an ESL tone arm on a single-speed Gray turntable.
Production years for the N21D are not documented in the available material, and the exact introduction date isn't pinned down. The stylus was on sale by 1961, when it appears in both Shure's catalog literature and the independent press. Original pricing is well established: $12.50 as a standalone stylus upgrade, $36.75 in the M7/N21D combination, $47.25 in the M3/N21D combination. Beyond that, the record is thin. No full standalone laboratory test of the N21D appears to have survived in this archive, and the review quotes that circulate mostly come from Shure's own advertisements reprinting earlier coverage.
For a collector today, the N21D matters for a practical reason: it is the part that wears out. Original styli are the limiting factor on any of these cartridges, and aftermarket replacements vary enormously in quality. A genuine N21D in good condition is worth more than the body it fits into, which is an inversion that would have surprised nobody at Shure in 1961 — they built the whole product line around the idea that the stylus is where the sound lives.
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