A magnetic cartridge, more commonly called a phonograph cartridge or phono cartridge or (colloquially) a pickup, is an electromechanical transducer that is used to play phonograph records on a turntable. The cartridge contains a removable or permanently mounted stylus, the tip - usually a gemstone, such as diamond or sapphire - which makes physical contact with the record's groove. In popular usage and in disc jockey jargon, the stylus, and sometimes the entire cartridge, is often called the needle. As the stylus tracks the serrated groove, it vibrates a cantilever on which is mounted a permanent magnet which moves between the magnetic fields of sets of electromagnetic coils in the cartridge (or vice versa: the coils are mounted on the cantilever, and the magnets are in the cartridge). The shifting magnetic fields generate an electrical current in the coils. The electrical signal generated by the cartridge can be amplified and then converted into sound by a loudspeaker.
History The first commercially successful type of electrical phonograph pickup was introduced in 1925. Although electromagnetic, its resemblance to later magnetic cartridges is remote: it employed a bulky horseshoe magnet and used the same single-use steel needles which had been standard since the first mechanical transfer disc record players appeared in the 1890s. This early type of magnetic pickup dominated the market well into the 1930s: by the end of that decade it had been superseded by the comparatively lightweight piezoelectric crystal pickup type, however the use of short-lived disposable metal needles remained standard. During the years immediately following World War II, as old record players with very heavy pickups were replaced, precision-ground and long-lasting stylus tips made of sapphire or the exotic hard metal osmium were increasingly popular. However, records made for home use were still made of the same abrasive shellac compound formulated to rapidly wear down the points of steel needles to fit the groove. The introduction of the 331⁄3 rpm record LP "album" in 1948 and the 45 rpm record "single" in 1949 prompted consumers to upgrade to a new multi-speed record player with the required smaller-tipped "microgroove" stylus. Sapphire and diamond then became the standard stylus tip materials. At first, the new styli came installed in smaller, lighter piezoelectric crystal or ceramic cartridges of the general type found in inexpensive self-contained portable record players throughout the phonographic era. Ceramic cartridges continue to be used in most of the "retro" and compact record players currently being made, in part because they are comparatively robust and resistant to damage from careless handling, but mostly because they are inexpensive. However, during the 1950s, a new generation of small, lightweight, highly compliant magnetic cartridges appeared and quickly found favor among high-fidelity enthusiasts because of their audibly superior performance. The high compliance also reduced record wear. They soon became standard in all but the cheapest component audio systems and are the most common type of pickup cartridge in use today.
Design and construction The cartridge consists of several components: the stylus, cantilever, magnets, coils and body. The stylus is the part that, when in use, is the interface with the record surface and tracks the modulations in the groove. It is typically made of a small polished diamond or other industrial gemstone. The cantilever supports the stylus, and transmits the vibrations from it to the coil/magnet assembly. The former is typically made of boron or aluminium, and previously beryllium although some manufacturers market models with exotic gemstone cantilevers. Most models of moving magnet cartridges have detachable stylus–cantilever sub-assemblies that allow for their replacement without the need to remove and replace the entire cartridge when the stylus has become worn. Coupled to the tonearm, the cartridge body's function is to give the moving parts a stationary platform so that they can track the groove with precision.
Types In high-fidelity systems, crystal and ceramic pickups have been replaced by the magnetic cartridge, using either a moving magnet or a moving coil. Compared to the crystal and ceramic pickups, the magnetic cartridge usually gives improved playback fidelity and reduced record wear by tracking the groove with lighter pressure. Magnetic cartridges use lower tracking forces and thus reduce the potential for groove damage. They also have a lower output voltage than a crystal or ceramic pickup, in the range of only a few millivolts, thus requiring greater amplification.
Moving Magnet (MM) and Moving Iron (MI) cartridges In a moving magnet cartridge, the stylus cantilever carries a tiny permanent magnet, which is positioned between two sets of fixed coils (in a stereophonic cartridge), forming a tiny electromagnetic generator. As the magnet vibrates in response to the stylus following the record groove, it induces a tiny current in the coils. Because the magnet is small and has little mass, and is not coupled mechanically to the generator (as in a ceramic cartridge), a properly adjusted stylus follows the groove more faithfully while requiring less tracking force (the downward pressure on the stylus). Moving iron and induced magnet types (ADC being a well-known example) have a moving piece of iron or other ferrous alloy coupled to the cantilever (instead of a magnet), while a permanent, bigger magnet is over the coils, providing the necessary magnetic flux.
Moving Coil (MC) cartridges
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