The audio amplitude from electret microphone is less than 20mV. To drive speaker we need more power in the audio signal. To amplify the audio signal from microphone we can use operational amplifiers such as LM358. Here electret microphone amplifier is build using LM358 op-amp. We will using single supply of +5V.
The following is circuit diagram that amplifies the audio signal to few volts swings.
In the above circuit a 2.2KOhm resistor is used to power on the FET which is found inside the electret microphone.The microphone has capacitor which changes its value when the audio hits the capacitor. The capacitor C1 is used to couple the audio signal into the amplifier stage. The audio LM358 amplifier is used in non-inverting configuration. The resistors R2 and R3 is used to bias the op-amp to mid-range value between +5V and ground. The resistor R4 is used as feedback resistors which along with variable resistor RV1 creates a voltage gain. The capacitor C2 is used as bypass capacitor and the capacitor C3 is used to reduce noise from the power supplies.
References
[1] Electret Microphone Preamplifier with OPA365
