Saturday, September 25, 2010

48V Phantom Powered Electret Condenser Microphone

Electret mic in brass casing
The design for these phantom powered electret microphones was taken from Scott Helmke's website, and is based on a Schoeps microphone design.
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.




Schematic and modification of electret microphone capsule.
Veroboard Layout
Designed to fit inside metal tubing.
Electrolytic caps are folded over to reduce circuit height.
If you cannot find 2n5087 PNPs, you can use BC557 as an alternative. Be aware that the pinout is opposite, so the package will be soldered facing the opposite direction.
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.









References:
http://www.scotthelmke.com/phantom-power-2.jpg
http://mp3forkidz.com/mic/msmicV2.html
http://sound.westhost.com/project93.htm

A much simpler design, powered from a 9V battery is available here:
9V Panasonic Electret Mic