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A compact, versatile, and reliable hydrophone preamplifier designed for use in multiple hydrophone arrays is described. The preamplifier is used in the frequency range 2 to 5000 cps (−3 db points) and has a dynamic range in excess of 80 db. The equivalent electrical self‐noise is below that of a sea state 0. One vacuum tube for impedance matching and seven transistors for voltage and power amplification are used in the preamplifiers. A total of up to 5 preamplifiers is contained in a cylinder 6 in. in diameter and 12 in. in length. A large amount of negative feedback is used to insure gain stability. The preamplifiers are designed for use with crystal hydrophones with sensitivities greater than −110 db re 1 v/μbar and capacitances of more than 5000 μμf.