Interested to hear that the Chinese have detected a couple of audio events in the Indian Ocean, with one of these hydrophone thingamajigs! since the manufacturing is probably offshore these days. http://youtu.be/vncBFLtLRc0 Maybe something's a little loose on the PCB. I would rather hang on for what HMS Echo has to say on the subject. Well taking into account the rather superior signal to noise ratio available from my slightly modified ex RN STC hydrophone pre amplifier. It's full of naughty Western Electric audio transformers and has amazing build quality: all germanium transistor built on turrets with daven switches and Connor sealed wire wound potentiometers. My bass sounds amazing via it.