|Electret mic in brass casing|
A Panasonic electret microphone capsule is modified by cutting the trace connecting the capsule casing from the internal FET source. Three wires are then connected to the microphone. The result is a greater tolerance for high SPL.
Designed to fit inside metal tubing.
Electrolytic caps are folded over to reduce circuit height.
Here is a populated veroboard. I have used BC557 in this case.
Modified mic capsule wiring.
The modification of the panasonic electret capsule permits a much greater bias voltage across the microphone's capacitive plate, while retaining a suitable working voltage across the internal FET circuit. The modification also produces a balanced audio output.
Bill of materials for circuit.
A much simpler design, powered from a 9V battery is available here:
9V Panasonic Electret Mic