A DIY hydrophone for balanced input. It's for stationary or drifting usage, since it will cause significant flow noise due to the non streamlined box. Piezoelectric disks inside a small metal box,used for paint. They are superglued to the inside of the lid. The black goo is liquid gasket.
https://github.com/Supermagnum/hydrophone/blob/main/IMG_20210713_143632.jpg https://github.com/Supermagnum/hydrophone/blob/main/IMG_20210713_155855.jpg https://github.com/Supermagnum/hydrophone/blob/main/IMG_20210713_155857.jpg https://github.com/Supermagnum/hydrophone/blob/main/IMG_20210713_155905.jpg https://github.com/Supermagnum/hydrophone/blob/main/IMG_20210714_003702_205.jpg https://github.com/Supermagnum/hydrophone/blob/main/IMG_20210714_003702_212.jpg https://github.com/Supermagnum/hydrophone/blob/main/IMG_20210714_003702_220.jpg https://github.com/Supermagnum/hydrophone/blob/main/IMG_20210714_003702_228.jpg
They eye bolt is there so a small weight or line can be attached, but since the box is to be filled with epoxy it will sink. It will be somewhat directional to the side of the piezoelectric discs. The zip tie is secured with a drop of superglue.
Preamplifier and impedance buffer: https://github.com/Supermagnum/piezoelectric