The High-Fidelity Phonograph Transducer
High fidelity began in earnest with the adoption to the phonograph of electrical transduction an amplification. Phonograph pickups had been patented as early as 1918, nevertheless, they do not appear to have become widely used until the late 20s and the early 30s, at which time measurement procedures and improved understanding of stylus-groove relationships provided a basis for high fidelity developments that followed. The renaissance of the phonograph after the depression of the 30s was spearheaded by the development of the Bimorph Rochelle salt crystal element and the invention of the lever-type pickup which allowed the stylus bearing loads to be reduced by half an order of magnitude. Crystal pickups were dominant until the 50s when they began to be displaced by barium titanate and lead zirconium titanate ceramics, with the piezoelectric principle in various forms being successively adapted to the LP record in 1948 and the stereo record in 1958. The renaissance of the magnetic pickup was presaged by the development of an ultralight moving conductor reproducer during the 30s and followed by the wide adoption of the variable reluctance principle after World War II. A quantum drop in stylus bearing forces again occurred with the disc in 1960. fidelity was further improved with the introduction of bi-radial styli for audio-frequency records and of pyramidal and Shibata styli for ultrasonic carrier-type discs. An indispensable pickup element, the pickup arm has undergone considerable improvements with the better understanding of the optimum arm geometry which has resulted in virtual elimination of tracking error inherent in pivoted arms. In a cogent manner, side thrust caused by the stylus-arm friction has been compensated with simple spring or weight mechanisms. For high-fidelity performance it is essential that the arm be properly damped. Two damping arrangements are described and their characteristics analyzed. Pickup equalization circuits are briefly treated. Among the problem areas still in need of improvement are a continuing lowering of stylus bearing forces; protection of stylus against damage; improved arm damping techniques; control of vertical stylus tracking angles; and reduction of stylus/groove resonances.
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