Microphone Pre-amplifier

A MICROPHONE AMPLIFIER

This is a microphone preamplifier: It is designed specifically for a transmitter, such that the output can be fed directly into a balanced modulator. However, it could have other uses, from time to time. This circuit has decoupling for RF, such that we do not find the Radio Frequencies that might otherwise reach through the amplifier.

There are two stages to this amplifier: They are both very similar in design. Indeed, the only real difference between the two stages is the filtering, coupling and roll-off afforded by the RC networks.

Dynamic range: The circuit is designed to operate from 20 mV to 200 mV input, without clipping. This is enough dynamic range to cover a large range of microphone types.

Quiescent current draw: This amplifier draws approximately 3.6 mA at 12 Volts supply.

Gain: Despite the two stages, the design restricts the gain to approximately 10 X the input voltage.