It is a home made measure microphone based on schematic of Eric Wallin Preamp2. Panasonic WM61A is at the end of a pipe with an external diameter of 3/8 inch and the preamplifier in ¾ inch pipe. The cable was made of 2-wire twisted pair with a shield. Supply of 9V battery connected on the plug side for the measurement time.
The PCB's dimensions are: 100x17mm.
Some of the components are placed on the side of print, so they fit the ¾ inch pipe.


Original device can be found at: LINK

Link to original thread (useful attachment) - Mikrofon pomiarowy z wbudowanym przedwzmacniaczem