IC power amplifier II BA546
In this project, we're going to make an audio amplifier using the power amplifier IC. As said in the last project IC power amplifier, you can change the gain of this IC by turning S1 ON and OFF: it is about 9 when S1 is turned OFF, and increases to about 33 when S1 is turned ON.
Now, let's get to the experiment using the earphone as a microphone. Turn power ON, and speak into the earphone while turning the control volume. When you turn the control volume completely clockwise, you'll notice your voice becomes louder, but not very loud. See what happens when you turn S1 ON. Your voice becomes much louder because of the increased gain. Adjust the control volume to a suitable level and practice speaking over the microphone.