Step 1: Materials
1 10 ohm resistor
1 potentiometer between 1k and 10k, this is your volume knob so its really your choice.
2 470uF electrolytic capacitors
1 3.5mm audio aux jack
A power source, I'm using a 12.5 regulated power supply, you can go as low as 10 volts and as high as 22 volts. 8 AA batteries would run it nicely if you're looking to make it portable.
Step 2: The Circuit
Then connect your positive power source to pin 14 through a 10 ohm resistor. And connect pin 14 to ground through a 470uF capacitor. The negative lead should be connected to the negative rail.
Now connect your common input of the 3.5mm jack to ground and the right and left both to the left pin of the potentiometer. The middle pin should be connected to pin 2 of the lm380 and the right pin should be connected to ground.
Now put a 470uF capactor from pin 8 to the positive terminal of your speaker (Negative lead of capacitor connects to the speaker) and the negative speaker wire should be grounded.