Electrical Reproduction from Phonograph Records

A new and improved tool generally means new or improved accomplishments. Great improvements in sound recording and reproduction have been made possible by the thermionic amplifier. Electrical reproduction may be considered in three steps, (1) generation of a voltage by the vibrations of the needle, (2) amplification, (3) conversion of electrical power into sound. The first of these steps involves some interesting mechanical and electrical problems, and it is with these that the paper primarily deals, the problems of amplification and loud speaker design having been discussed in earlier publications to which references are given. Several types of phonograph ``pick up'' are possible; electrostatic, piezoelectric, electromagnetic, and variable resistance or microphonic. The electromagnetic principle is used in the device now manufactured. Since the moving armature cannot be actually at the needle tip, the little generator must function by transmitting the vibrations from the needle tip through a more or less flexible structure to the armature. Vibrations are inevitably transmitted, but when the requirements of freedom from appreciable distortion and maximum possible output are added, extreme care in design becomes necessary. An analysis is given of the mechanical behavior of the present model of reproducer.