tekHPoynt

H
ere's the first electronic project I would be sharing for our hobbyist, students and other techies. I suggest to try all the electronics projects I published on the "bread board" first before implementing them on the PCB. If the schematic doesn't work in the first place that would be the most fun as you have chance to debug the circuit and learn as you go along.

As the signal from a microphone is too weak for a standard line input. This low-noise DC-coupled microphone amplifier provides a solution for anyone who wants to connect a microphone to his/her Hi-Fi installation. Below is the schematic diagram of a Low-Noise Microphone Amplifier.

A differential amplifier is built around T1(MAT-03E), which is a low-noise dual transistor(if you got other alternative parts, please try it). The combination of T2 and LED D1 forms a constant-current source for the input stage. A low-noise op-amp(OP-270E) amplifies the difference signal that appears at the collectors of the dual transistor. The result is an analog signal at line level. The bandwidth of the amplifier ranges from 1Hz to 20kHz. Within the audio range (20Hz to 20kHz), the distortion is less than 0.005 percent. Since only half of the OP-270E is used, the remaining op-amp could be used in the output stage of a stereo version.

The amplifier can be powered from a stabilized, symmetrical supply with a voltage between +/-12V and +/- 15V. Such supply voltages are already present in many amplifiers.