Thank you Alex, I will give it a try and will report back on the forum. I was afraid of introducing a filter in the audio line, but, when I understand the circuit correctly, this configuration would result in a high pass filter of 5-10 Hz, which is no problem for me.

Hi Alex, I would be using Audiomoth 1.2.0 as USB mic device or Audiomoth USB microphone, probably the latter, so without the battery holder. Do you mean the hydrophone needs to have a DC offset voltage with PIP active or with the resistor removed? Is there no capacitor in the audio input line to the preamp to remove any DC offset and PIP DC? My guess would be the first 20 dB preamp does not need any DC....? My hydrophone has a built in preamp 20dB powered by a 9V battery, the signal is balanced XLR, but I will use only one pin (unbalanced) to connect to the Audiomoth USB mic connector. Actually, I hope it will not have any DC offset.

Hi Brian, One of my Audiomoths in IPX7 case was hidden near a ditch. It was left there for ten days. When I collected it, it was half under water, mic in air. Inside was completely dry, and AM was still recording. When I checked the recordings, it had been completely under water for over 24h. Whilst under water, recordings were very faint. After 24h mic was apparently back in air and recordings were fine as always.

After some weeks of experience with different configurations it is clear to me that using short cycles like 0/10 (seconds sleep/record) resulting in many files written to SDcard decreases runtime. Changing cycle period from 0/10 to 5/295 increased runtime from 3,5 days to at least 6 days, probably over 10 days on 3 Energizer Lithium 1,5V AA batteries. Triggering does not seem to affect power consumption.