Some aspects of gramophone pick-up design

The mechanical problems involved in ensuring that a disc-reproducing stylus follows with sufficient accuracy the path cut during the recording process are discussed. The modulated groove acts upon the spherical stylus as a moving plane inclined to x-, y- and z-axes, and forces are therefore generated in unwanted directions which can result in a form of distortion (translation distortion). The magnitudes of these forces and their influence on the effective path of the stylus are approximately analysed in terms of groove and pick-up parameters. Attention is drawn to the fundamental difference between the actions of the stylus in tracing lateral and vertical modulation, and to the conditions necessary for the maintenance of continuous two-point contact between stylus and groove. An approximate analysis is given from which a pick-up´s `modulation capability¿ may be assessed. The playing weight is of major importance in this connection, and the factors influencing the choice of an appropriate value are discussed, with reference to both single-channel lateral and 45/45 stereophonic records. Finally a pick-up designed in accordance with these principles is briefly described.