Hydrophone preamplifier

Abstract

A hydrophone preamplifier design utilizing hybrid integrated circuits, surface mounted components, multi-layered circuit boards and gain switching. Acoustic signals from a sensor are applied to a hybrid integrated circuit preamplifier whose gain is controlled by a relay activated remotely from a control that allows a predetermined attenuation permitting measurements of high sound pressure levels (low gain) or low ambient noise levels (high gain). The preamplifier in the hybrid integrated circuit provides a gain of 10 (20 dB) and an additional gain of 10 is provided by a low-noise operational amplifier (op amp). A current booster provides the output current drive capability for the preamplifier which is capable of driving large capacitive loads and has protection against both electrical and thermal overloads. Insertion calibration is provided through an ac current signal supplied by an external source, which develops a small voltage signal when supplied to the preamplifier. The voltage signal is coupled through an acoustic sensor to the preamplifier input providing a complete loop-back system test.

What is claimed is: 
     
       1. A hydrophone preamplifier comprised of: an electrical input signal from an acoustic sensor;   a hybrid integrated circuit preamplifier receiving and first amplifying the electrical input signal;   means for providing an additional gain to the first amplified electrical signal so as to produce a second amplified signal;   means for boosting the current of the second amplified electrical signal to provide an output current drive to a transmission cable;   means for providing electrical power to the preamplifier;   means for calibrating the preamplifier by applying an alternating current signal through the acoustic sensor to the hybrid integrated circuit preamplifier; and   means for controlling the gain of the electrical input signal applied to the hybrid integrated circuit preamplifier.