Description:

This microphone amplifier is based on the LM358 operational amplifier. The signal from the microphone goes through the blocking capacitor C1 and the resistance R4 to the inverting input (pin 2) of the operational amplifier. The signal gain is determined by the value of the variable resistor P1 and R4 according to the formula Ku = - P1 / R4. The gain shows how many times the voltage of the output signal is greater than the input. The minus sign means that the phase of the output signal is opposite to the input signal, that is, the amplifier is inverting. In this scheme, the gain is 1000. This is necessary to significantly amplify the weak signal that the microphone gives out.

Resistor R5 and capacitor C2 form a filter that suppresses noise coming through the power circuit. The filter is needed so that noise does not penetrate the amplifier input and does not mix with the useful signal coming from the microphone. Resistance R1 sets the operating current through the microphone, its value is determined by the type of microphone used.

Capacitor C1 separates points with different potentials between the output of the microphone and the input of the operational amplifier, and also passes an alternating current, which is a useful signal. For normal operation of the operational amplifier, with a unipolar supply, a constant voltage equal to half of the supply is supplied to the input (pin 3). Resistancelien R2 and R3 form a voltage divider. Elements C3, C4, D1, D2 form an amplitude detector that converts alternating voltage to direct voltage. Resistance R7 is the load of the amplitude detector. This resistance is needed so that in the absence of a useful signal at the input, the capacitor C4 can be discharged, and the output voltage of the amplitude detector becomes zero.

The technical features:

• Frequency range: 20 Hz … 25 kHz.
• Ability to adjust the gain: 100 … 1000.
• Supply voltage: 5 … 12 V.

Contents in the package:

• Radio components.
• Printed circuit board.
• Case parts.
• Fasteners.
• Instruction.

Additional Information:

• Installation and soldering of radio components must be done by yourself.