An Amplifier


The Amplifier takes an electrical signal and makes the signal stronger, and in the end, louder. Because the signal is strengthened by an amplifier, you can play music through higher resistant speakers. This amplifier is a solid-state-hi-gain design and is intended to run through an 8 ohm speaker. The amplifier schematic was originally designed by Ed Vogel and Blind Lightnin' Pete from MAKE Magazine.

The heart of the circuit is the operational amplifiers, or op amp. The op amp is an IC that produces an output voltage hundreds of thousands of times larger than the voltage difference between its input terminals:
Where V+ is the voltage at the non-inverting terminal, V- is the voltage at the inverting terminal and AOL is the open-loop gain of the amplifier (the term "open-loop" refers to the absence of a feedback loop from the output to the input).

The LM386 is a popular audio amplifier chip that allows a user to amplify sound.

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1 and 8: The gain control of the amplifier. You can adjust the gain by connecting a variable resistor, like a potentiometer, a resistor and capacitor or just capacitor between these terminals.
2 and 3: The sound input signal terminals. These are the terminals where you place the sound which you want amplified. Terminal 2 is the -input and Terminal 3 is the +input.
4: GND (ground)
5: The output of the amplifier. This is the terminal in which the amplified sound signal comes out.
6: The terminal which receives the positive DC voltage so that the op amp can receive the power it needs to amplify signals.
7:The Bypass terminal. This pin is usually left open or is wired to ground. However, for better stability, you can add a 10µF capacitor to prevent oscillations in the op amp chip.

The LM386 takes anywhere from 4-12 volts of DC voltage to operate.