12v to 5v 100 mA Linear Regulator PUBLIC

A small, quiet, and simple regulator circuit to provide correct bias voltage to a dynamic microphone when replacing an electret microphone for amateur radio use.

Some Yeasu portable amateur radios put out an 8-9v bias voltage for an electret microphone (e.g., FT-2980), but use of a dynamic microphone (such as a Yaesu M-90D) requires a 5v bias volatage, and the 8-9v provided from the radio would be outside of the microphone voltage parameters, and would likely cause damage.

Using a USB or other power source might be sufficient, but might also create EMI or other noise that would be detrimental to a clean signal

This is a simple circut using a linear regulator that should be extremely noise free, and provide a regulated 5v for bias voltage. The M-90D should draw no more than 15 mA, and the design of this circuit should be capable of putting out 100 mA maximum. The fuse is rated at 100 mA, and is a precaution should the protective features of the 78L05 fail. A PPTC could be used in place of the fuse, although it would likely be slower acting, but should still be sufficient.