The integrated chip LM386 is a low power audio frequency amplifier requiring a low level power supply (most often batteries). It comes in an 8-pin mini-DIP package. The IC is designed to deliver a voltage amplification of 20 without external add-on parts. But this voltage gain can be raised up to 200 (Vu = 200) by adding external parts.
The external parts shown on diagram 3.1 can be selected to get the desired gain. Circuit A will give a voltage amplification of 200. Circuit B will give a gain around 50. The circuit C is not for voltage amplification but will raise the bass level by about 5 dB. Take note that the circuit C is to be connected between pins 1 and 5 of the IC.
The power output is around 550 mW at 16 ohm speaker impedance. This audio frequency amplifier is ideal for small battery powered devices.
If you use the external circuit A, replace the Rx with a jumper wire in the PCB.
If you use the external circuit C, solder the additional resistor and capacitor to the PCB points labeled Rt and Cy.