Microphone preamp

This little preamp has a gain of about 100 to 1000, depending on the supply voltage, and the used FETs. It is a shunt regulated push-pull stage, with low distortion, relatively low noise (due to the use of jFETs), a high input impedance, a low output impedance and high gain. If you run it out of a battery you should place a 100uF cap over the supply rails. Originally the design was a tube amplifier for turntables, the FETs were one stage of a 12AX7. Remarkably is the fact that this circuit is not feedback, but has very good linearity. It is possible to raise R2 and R3 to obtain high gain.