This small amplifier is perfect for Audio circuit designer or mad lab scientist.

It uses minimal components, is really simple to assemble and will provide enough power so you can hear what's going on in your circuit.

This amp can provide something like 700mW according to the datasheet. I could drive a 2-3-4 Watts speaker really easily and the sound was still clean even at maximum volume.

Make sure the speaker is 4-6-8 ohms.

If you want to skip the tutorial and watch the process of making the amp, it's here, else, scroll down:

Supplies

9V Battery
9V connector
2 Pin Terminal Block (3x)
1/4 audio jack (optional for guitar input)
1/8 audio jack (for phone input)
Wires
Speaker 4-8 ohms (2-3 Watts)
10K ohms Potentiometer (volume for input)
10 ohms Resistor (1/2 watt)
10 uF Capacitor
0,047 uF Capacitor (473) instead of the 0,05uF
220 uF Capacitor instead of the 250uF
0,1 uF Capacitor (104)
Prototype Board (Vero Board)
IC : LM386
DIP 8 socket (optional)

Step 1: Getting to Know the LM386

This IC is fairly easy to understand and tho, even if you don't understand fully the theory behind it, you should be able to complete the circuit without any problem. Unlike other regular OP Amp, the LM386 is capable of outputting enough power and driving a small speaker directly, this is why it is perfect has a Bench Lab Amplifier. This is a test amplifier and not a high quality amplifier, please note the differences.

Pin 1 and 8 are the gain, by adding a capacitor between these two pin, you'll set the gain to 200.
If the gain of 200 is too much for you, well, you could add a resistor in series with the capacitor but the way I see thing is else way.
I prefer to add a 10K ohm resistor at the input of my Amplifier to control the gain directly before it enters the IC. This allows a good control of the volume and ensure that the amplifier is always working at full capacity.
If you want that amplifier to have a gain of 20, leave the pin 1 and 8 open.

The pin 6 is for the positive Supply. You may use 4 to 12V maximum. In my case, I'm using a 9V battery, it is safe, noiseless and provide a great output to the amp.
The pin 4 is the ground or the negative supply. Make sure it is connected to all the other places where there should be ground.

The pin 2 is the inverting input, in most case where you use an OP amp, you would have to do something special with this pin, either bias it or create a reference voltage. But in our case, this circuit is so easy that we only plug this pin to the ground.

The pin 3 is the non-inverting input , this is where you will connect your input signal.

The pin 5 is our output, this is where the amplified sound will come out. Which by means, this is where we will plug our small speaker.

The pin 7 is not used, don't complicate your life, I didn't do anything with this pin and it's working fine.

Step 2: Assembling Everything

You may assemble this circuit on a breadboard, if you do so, keep all the wires as short as possible since it will help eliminates noise.

If you prefer, this is the right time to solder everything on a perf board, or a vero board.

The schematic is pretty straightforward and shouldn't be complicated.

See this video for the complete process :

My Small Amp is still on a perf board but you may house everything into a small plastic or metallic case, let me know how you build yours and I'd like to hear it in action.

Hope you enjoyed the process and that everything was clear enough.