A stereophonic ceramic pickup cartridge for two-gram tracking

The pickup described will track with a vertical force of 2 grams, on simple but properly designed tone arms. It has a mechanical compliance 6 cm × 10-6/dyne and an effective mass of about 1.4 mg. Output is 0.35 volt. A combination of optimum rubber properties and viscous damping provide a response free of resonances. The design is well suited for quantity production for the home phonograph market. Another paper describes successful tracking of this cartridge in commercially available record changers. In a pickup destined for quantity production, several design factors must be met in order to maintain uniform high performance. It is important that the two ceramic elements be correctly positioned during assembly. In the present design this is done by means of octagonal rubber element mounts which are placed into two semioctagonal channels on mating interfaces of two plastic housing parts. In any two-element stereophonic pickup design, a "coupler" is needed to join the two elements to a single stylus arm. Design of the coupler has important bearing on distortion, output level, channel separation, and mechanical impedance. Coupler requirements in the present design have been met by proper configuration and choice of material. Another important design factor is the means provided for pivoting the stylus level arm. For lateral motion, at the stylus, compliance must be high for lateral motion in two degrees of freedom. Rotational compliance, about the lever axis, must be low in order to avoid undesirable rotation of the lever arm. There must be no lateral freedom at the pivot point. Longitudinal compliance of the level arm must be low in the direction of drag from the record groove to avoid frequency modulation effects. The stylus lever mounting arrangement described achieves these design requirements in a simple assembly. A light tube, comprising the lever arm, is flattened at its pivoted end in a manner to produce tapered shoulders. These shoulders are brought to bear against a hole in a small rectangular metal enclosure which is filled with a plastic material having viscoelastic properties. The potting arrangement damps any lever resonances and provides a small restoring force to position the lever for engaging the coupler during change of styli.