Aiming at the characteristics of complicated environment and multiple noise sources for underwater acoustic sig-nal, an ultra-low noise amplifying circuit based on JFET is proposed. This circuit adopts 2 low noise JFETs 2SK170 as the first stageamplifiers , which is connectd to in-phase amplifying circuit through CR high-pass filtering, and the gain of overall circuit is up to 70dB. In order to further enhance SNR of received signal, a high-Q frequency selective circuit is optimized and designed in combina-tion with the characteristic of dual-T filter. The Multisim 14 simulation results show that the voltage noise density of the designed cir-cuit under 1 Hz is only 2.4 nV/Hz0.5 , and the filter's Q value can reach 25.6. Combined with actual test results , the designed circuitis proved to meet underwater acoustic measurement requirements.
