Portable Microphone Preamplifier Circuit Diagram – Build Your Own!

Circuit Diagram

Components:

Device Purpose:

This circuit is primarily intended to furnish common home stereo amplifiers alongside a microphone input. The battery supply represents a favorable compromise; in this manner, the input circuit remains immune to low-frequency interference from mains power and simplifies connections to the amplifier due to the absence of a mains cable and power supply.

When a stereo microphone is utilized, the circuit should be duplicated. In this case, two individual level controls are preferable to a dual-ganged stereo potentiometer. The circuit’s low current draw (approximately 2mA) ensures a prolonged battery lifespan.

Circuit Operation:

The circuit relies on a low-noise, high-gain two-stage PNP and NPN transistor amplifier, employing DC negative feedback through R6 to stabilize operating conditions with notable precision. The output level is attenuated by P1, concurrently reducing the stage gain due to the elevated value of R5. This distinctive arrangement of P1 yields a high input headroom, enabling it to manage a broad spectrum of input sources (0.2 to 200mV RMS for a 1V RMS output).

Notes: