Everything you need to know about cartridges & diamond styli.

The MMC design was invented and patented by Bang & Olufsen and introduced back in 1959 for the SP1-2. The MMC cartridge is a variation of the Moving Iron (MI) design. Magnets and coils are stationary, while a micro-cross moves with the cantilever, thereby varying the distance between the arms of the cross and the magnets. The MMC design enables superior channel separation, as the movements of each channel occur on a separate axis.

Nude diamond vs. tipped diamond

The diamond is an extremely important part of a hi-fi cartridge; learn more about them here:

a: Nude diamond
The diamond is a whole diamond, specially shaped and glued or fixed to the cantilever.

b: Tipped diamond
Here a diamond tip is mounted in a metal shank that is fitted to the cantilever. Such a shank increases the total mass of the diamond tip and thus degrades the transient response of the cartridge compared to a cartridge that uses a nude, non-tipped diamond.

There are several different diamond profiles, and the most important ones are described in the following sections.

Spherical stylus and elliptical stylus

The spherical stylus:

The spherical stylus is the simplest and cheapest to produce, and is therefore the most common. Spherical styli can be recommended in cases where robustness and economy are the main considerations when buying a cartridge.

The elliptical stylus:

The elliptically shaped stylus more closely resembles the triangular cutting stylus used for cutting master discs.

The elliptical stylus is able to follow the record groove modulations more precisely than spherical types, and its distortion and phase error will therefore be lower. In the outer part of the groove, where the diameter is largest, it can be difficult to hear the difference between a spherical and an elliptical diamond, as there is relatively more space in the groove for the highest frequencies. But in the inner part of the groove, the wider radius of the spherical diamond makes it difficult for this shape to trace the finer groove undulations. This can attenuate the treble and lead to audible distortion in difficult passages.

There was a time when experts disagreed about the choice between spherical and elliptical stylus types. This debate can now be regarded as settled, and today there are very few, if any, quality cartridges supplied with spherical styli. Spherical styli can be recommended for old mono records from the late forties to the early sixties, as the grooves on these records are wider.

Other stylus types

The introduction in 1971 of quadraphonic record playback based on the CD-4 system started a completely new development in the hi-fi cartridge field. Cartridges for CD-4 records must be able to reproduce frequencies up to 45,000 Hz. This was more than the models that existed at the time could handle, as the contact area of the elliptical diamond itself is too wide for a 45,000 Hz vibration to be traced accurately. One solution to the problem could have been a sharper grinding of the elliptical diamond to achieve a reduced horizontal contact area. However, this would significantly increase wear on the groove surface.

The Japanese scientist Shibata took a completely new direction and invented the special stylus profile that now bears his name. The Shibata profile is characterised by having the required small contact area in the horizontal plane for playback of the ultra-high frequencies found on CD-4 records. In the vertical plane, the special shape of the stylus provides a wider contact area than is the case with either spherical or elliptical styli. This means that a Shibata-shaped stylus, despite its high-frequency capabilities, causes less record wear than traditional stylus profiles.

Various cartridge manufacturers have been inspired by the Shibata profile and now produce cartridges with stylus shapes that provide the same benefits as Shibata. These have names such as bi-elliptical, pramanic, quadrahedral, hyperbolic, pathemax and Fine Line. Although CD-4 and other quadraphonic systems never really caught on with consumers, they helped to accelerate the development of stylus types that improve the playback of stereo records in the form of more accurate treble reproduction, lower distortion and reduced record wear.

A record groove showing the angles of different stylus types in relation to the groove when tracing the modulation. The elliptical and Fine Line styli are able to follow the groove modulation more precisely than the spherical type. This gives lower phase distortion.

a) Cutting stylus
b) Spherical stylus
c) Elliptical stylus
d) Fine Line stylus