Piezo-electric crystal pick-ups

The crystal elements as used for pick-ups are exclusively bimorphs, usually torsional in the case of Rochelle Salt, and always benders in the case of barium titanate. In the design of pick-ups, free use is made of electromechanical analogues, and the equivalent electrical circuits with mechanical constants for all forms of transducers have been evaluated with a high degree of accuracy. By suitable mechanical design, the needle tip impedance of a pick-up may be reduced till the, pick-up will satisfactorily track commercial records at needle pressure of less than 5 gm and the overall frequency response made flat with very simple equalizers from 20 c/s to 20,000 c/s. Record wear and stylus wear are intimately connected and, for a constant record material, they are usually a function of the needle tip impedance. The distortion generated in the system may be made negligibly low, but recent tests have shown that very high intermodulation distortions can occur in both magnetic and crystal pick-ups at frequencies corresponding to the low frequency tone arm resonance and sub-harmonics of the high frequency stylus system resonance. Electrical and constructional details are given of a double sapphire stylus pick-up for 78 and 33¿ r.p.m. records.