Connecting piezoelectric pickups to magnetic-pickup amplifiers

The majority of phonograph pickups and pickup amplifiers in use today fall into two classes: (1) Velocity-responsive (magnetic) pickups operating directly (or with the aid of a transformer) into high-gain amplifiers with input impedances of 20,000 ohms or more; and (2) displacement-responsive (piezoelectric) pickups operating into low-gain high-impedance amplifiers, with input impedance of the order of 1-5 MΩ. There is a general belief that pickups of Class 1 cannot be connected to amplifiers in Class 2, and vice versa. This belief is only partly correct. Magnetic pickups generate voltages of 10-30 millivolts at 1 kc on standani test records and require a degree of gain and compensation not available in amplifiers of Class 2. However, piekups in Class 2 often generate voltages of .2-.8 volts or more, and by use of simple networks can be used satisfactorily with amplifiers of Class 1. The author discusses a method for converting an amplitude-responsive pickup into a velocity-responsive pickup.