Microphone Preamplifier

Preamp Circuit Diagram

Geez, hope I do this post right...

The preamp as shown is not a good idea. The biasing for the transistor is poor. A far better idea is to use an N-Channel FET instead of the transistor. Almost any N-Channel FET is fine. That means it takes a " (+) " voltage.

Then use a high resistance from the "gate" (same as the base position in the schematic) to ground for bias. Remove the resistor shown from the base to the collector! Anything from ~100kohm up to ~1megohm will work super fine. The "drain" (collector) resistor should be set to make the gain correct, higher drain resistor = higher gain. Also, higher source (emitter position) resistor, LOWER gain, and more local feedback. Something in the 100ohms or greater range should be ok.

That depends on the voltage out of the electret mic element and the required voltage at the line in of your unit. The bias supply for the eletret mic should also be "decoupled" from the drain (collector) supply of the FET via a series resistor and a small cap (1ufd - 10ufd range) to ground.

You can also search the web for "Sigfried Linkwitz" - his site has the diagrams, schematics and and a mod for these elements. Typically a WM-60 Panasonic has flat response and is used often.