Abstract: A balancing apparatus particularly useful in a quadrature magnetic head pickup device employs separate amplitude and phase detecting circuitry. A phase detector provides a DC level indicative of a phase variation between a reference signal and a random signal to be compensated. A DC signal is provided which then causes a phase shifter to provide a square wave output indicative of a phase lag or lead, which phase signal is of a magnitude to compensate for the phase angle error of the random signal. An amplitude detector compares the amplitude of the random signal with a predetermined reference signal to provide another DC voltage signal indicative of the amplitude offset. The generated phase and amplitude signals are combined in a summing amplifier to provide an output signal which is fed back to the drive circuitry associated with a magnetic head to compensate for the random signal over a wide range of temperatures.

Abstract: A data storage retrieval system includes a magnetic circuit read head which comprises first and second pole members. Located and positioned between the poles is a pickup means which comprises a magnetic member having a pickup coil associated therewith. The member as positioned between the poles is located at a point which provides zero output across the coil when the poles are excited by a source of alternating potential. A magnetic material which may be positioned on an information carrying card is positioned such that it affects the flux lines between one of the poles and said pickup means. This position of the magnetic member serves to provide a signal across the coil indicative of a binary one or a zero.