This is a small PCB module, plus three suitable transistors.
It is an electret microphone capsule adapter to balanced XLR signals compatible with normal XLR mic inputs with phantom power such as on mixing consoled or audio interfaces etc.
This is for use in DIY microphones or such as adapting a "PC" or similar mic for use with an XLR input.
All connections are to solder pads, there are no plugs, sockets or enclosure included. It could eg. be used "inline" with some form of housing or protection, or fitted in an enclosure with input and output connectors to suit the application etc.
The mic gain is adjustable via a preset potentiometer on the module.
It is designed to operate from 48V phantom power, and provides 5V through a load resistor to the capsule input as well as a phase splitter and balanced line drive circuit.
The PCB is assembled other than fitting the three C1845 low noise audio transistors, which are supplied with with the PCB but not fitted, to allow people to used different types if they prefer.
The PCB size is approximately 41mm long by 18mm wide, and roughly 10mm height once the transistors are installed.
These are supplied with a copy of the schematic and connection instructions.
Full details including the schematic and a link to my video showing the connection & testing of one of these are here:
https://robert-jenkins.co.uk/site/index.php/electronics-and-audio/designs-projects/29-electret-mic-to-balanced-xlr-adapter-module
Note that these boards are designed to work with the common two-terminal type electret mic capsules that have a FET buffer amplifier built in, and use a bias resistor to a low voltage supply.
They may also work with some MEMS type mic capsules that also use a similar low voltage bias via a fairly low value bias resistor (2k2 - 10k) - but I do have any of that type to test.