Peeking inside a moving magnet phono cartridge and stylii

How does a wiggling groove on a rotating record transform into two-channel sonic excellence? It all starts with the turntable cartridge, mated to one of several possible needle types.

Mid-last year, I confessed that I’d headed back down the analog “vinyl” record rabbit hole after several decades of sole dedication to various digital audio media sources (physical, download and streamed). All three turntables now in my possession employ moving magnet cartridge technology; here’s what I wrote back in July in comparing it against the moving coil alternative:

Two main cartridge options exist: moving magnet and higher-end moving coil. They work similarly, at least in concept: in conjunction with the paired stylus, they transform physical info encoded onto a record via groove variations into electrical signals for eventual reproduction over headphones or a set of speakers. Differences between the two types reflect construction sequence variance of the cartridge’s two primary subsystems—the magnets and coils—and are reflected (additionally influenced by other factors such as cantilever constituent material and design) not only in perceived output quality but also in other cartridge characteristics such as output signal strength and ruggedness.

Miny-but-mighty magnets

And here’s more on moving magnet cartridges from Audio-Technica’s website:

Audio-Technica brand moving magnet-type cartridges carry a pair of small, permanent magnets on their stylus assembly’s cantilever. The cantilever is the tiny suspended “arm” that extends at an angle away from the cartridge body. The cantilever holds the diamond tip that traces the record groove on one end and transfers the vibrations from the tip to the other end where the magnets are located. These tiny magnets are positioned between two sets of fixed coils of wire located inside the cartridge body via pole pieces that extend outward from the coils. This arrangement forms the electromagnetic generator.

The magnets are the heaviest part of the moving assembly, but by mounting the magnets near the fulcrum, or pivot point, of the assembly the amount of mass the stylus is required to move is minimized, allowing it to respond quickly and accurately to the motion created by the record groove. In addition to enhancing response, the low effective tip mass reduces the force applied to the delicate record groove, reducing the possibility of groove wall wear and damage. The moving magnet-type cartridge produces moderate to high output levels, works easily into standard phono inputs on a stereo amplifier or receiver and has a user-replaceable stylus assembly. These cartridges have a robust design, making them an excellent choice for demanding applications such as live DJ, radio broadcasts and archiving.

The associated photo is unfortunately low-res and otherwise blurry:

Here’s a larger, clearer one, which I’d found within a tutorial published by retailer Crutchfield:

Inexpensively assuaging curiosity

Ever since I started dabbling with vinyl again, I’d been curious to take a moving magnet cartridge apart and see what was inside. I got my chance when I found a brand new one, complete with a conical stylus, on sale for $18.04 on eBay. It’s the AT3600L, the standalone version of the cartridge that comes pre-integrated with my Audio-Technica AT-LP60XBT turntable’s tonearm:

Here are some “stock” images of the AT3600L mated to the standard ATN3600LC conical stylus (with the protective plastic sleeve still over the needle):

This next set of shots accompanied the eBay post which had caught my eye (and wallet):

And, last but not least, here are some snaps of our dissection patient, first bagged as initially received:

then unbagged but still encased, and as usual (as well as with photos that follow) accompanied by a 0.75″ (19.1 mm) diameter U.S. penny for size comparison purposes:

along with mounting hardware at the bottom:

and finally, free from plastic captivity:

Conical closups and elliptical unpredictability

Next, let’s pop off the stylus and take a gander at its conical needle tip:

along with the cantilever and pivot assembly:

If you’ve already read my July coverage, you know that I’d also picked up an easily swappable:

elliptical stylus, the Pfanstiehl 4211-DE, which promised enhanced sonic quality:

but ended up being notably less tolerant than its conical sibling of any groove defects. Some of this functional variance, I noted back in July, is inherent to the needles’ structural deviations:

Because conical styli only ride partway down in the record groove, they supposedly don’t capture all the available fidelity potential with pristine records. But that same characteristic turns out to be a good thing with non-pristine records, for which all manner of gunk has accumulated over time in the bottom of the groove. By riding above the dross, the conical needle head doesn’t suffer from its deleterious effects.

But, as it turns out, the Pfanstiehl 4211-DE itself was also partly to “blame”. It reportedly works best with turntables based on the standalone AT3600L cartridge, whose tracking force and antiskating settings are both user-adjustable and lighter than those needed (non-adjustable, as well) with the fully integrated AT-LP60XBT turntable.

I resold the barely used Pfanstiehl 4211-DE on eBay and went with Audio-Technica’s (modestly) more pricey ATN3600LE elliptical stylus instead, which explicitly documented its compatibility with the AT-LP60 turntable series and indeed worked notably better with my setup:

Back to the ATN3600LC conical stylus. Two interior views showcase the magnets called out in the earlier concept image:

And here’s where they mate with the cartridge itself (with associated coils presumably inside, to be seen shortly):

Cartridge dissection

Next, let’s remove the screw that holds the top black plastic mounting assembly in place:

One more look at the connections at the back, with markings now visible:

And now, let’s peel away the metal casing, focusing attention on the top-side seam:

With that, the insides come right out:

That was a fun and informative, not to mention inexpensive, project that satisfied my curiosity. I hope it did the same for you. Sounds off with your thoughts in the comments, please!

—Brian Dipert is the Principal at Sierra Media and a former technical editor at EDN Magazine, where he still regularly contributes as a freelancer.

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