The goal of this project is to design a pre-amplifier for an electret microphone to bring the signal to “line in” level. Electrets are inexpensive, electrostatic capacitor-based devices that respond well to mid-range and high frequencies. An internet search will yield many examples such as https://cdnshop.adafruit.com/datasheets/CMA-4544PF-W.pdf. The electret microphone generally has a built-in FET amplifier that presents a high-impedance to the audio sensing device and requires a bias voltage to operate. Figure 1 below shows the electret microphone and the conventional interfacing components.
Within the microphone, the sensor is on the left and an N-channel JFET is on the right. The bias voltage is
usually in the range of 3 – 10 V and is applied through a resistor of 1 – 10 kΩ. A coupling capacitor is used to
block the DC signal and couple the output to an amplifier.
For this project, you will use a model for the electret microphone that is provided to you and implement a preamplifier that takes the microphone output and amplifies it to line level, i.e. the level that is needed when
sending the signal to most audio equipment.