FET Hydrophone Pre-Amplifier
Unwanted noise is eliminated by FET. FET also added capacitance caused by long cobias connecting hydrophone to shore station. Voltage gain is unity. Hydrophone preamp can be used with cables up to 3000 feet long. Use 1 Meg resistor between gate and ground to suppress low frequency excursions of signals if hydrophone moves in water.
[Circuit’s schematic diagram source: seekic.com]