“The project shown here is a microphone preamplifier that provides high quality amplification, optimized for use in computers, media and mobile applications. The pre-amplifier provides a differential input stage, making the device particularly effective when layout constraints force the microphone amplifier to be physically remote from the ECM microphone. This project features adjustable gain using PR1 trimmer potentiometer, very high power-supply rejection (95dB), and common-mode rejection (79dB), making it ideal for low-noise applications. Board is provided with condenser microphone as well as connector to connect external microphone, selection of external or internal microphone is possible with the help of on board Jumper. Circuit requires 5V DC input. The circuit provides differential output, use +OP/GND for single ended output. External microphone gain can be changed using R5.
The project features two selectable inputs onboard microphone or external microphone, differential outputs, adjustable gain, an integrated low noise bias source, and a low-power shutdown mode. Two input paths provide both differential and single ended microphone sensing. The high-noise rejection of the differential input is ideally suited to an internal microphone where system noise and long-run PC board traces can degrade low-level signals. The single-ended input provides a simple connection to an external microphone, can be connected to CN2.”