This is an LM386 audio amplifier that can be used with a small 9 volt Battery Operated,Current use as little as 5 milliamps.And amplification up to 500 mW.
This is The small tweeter speaker protection circuit It can be packed into any speaker cabinet, and does not require a power supply as well. [...]
We sometimes need a Simple microphone, But we cannot find it. This circuit can be help us modify the normal speaker to microphone as pre-mic circuit.