The LM386 IC provides a simple 0.25W audio power amplifier that runs on 9V battery and needs only a few passive components

The LM386 is a low-voltage audio power amplifier IC costing under $1. In its basic configuration (gain = 20), it requires: pin 6 (+V), pin 4 (ground), signal input at pin 3 through a volume pot, and a 250μF bypass capacitor from pin 7 to ground. Adding a 10μF capacitor between pins 1 and 8 raises gain to 200, suitable for high-impedance sources like contact microphones and coil pickups. The circuit puts out ~0.25W into a small speaker, sufficient for portable use with 9V battery or four AA batteries. The chip can also drive piezo disks at high sound levels when used with the backwards output transformer trick from the piezo driver chapter. Key caution: this circuit drains more battery current than the oscillator circuits—always use a power switch or disconnect the battery.

Examples

Basic config: 9V to pin 6, ground to pin 4, volume pot wiper to pin 3, 250μF from pin 7 to ground, 8Ω speaker at pin 5. High-gain config: same + 10μF from pin 1 to pin 8 (boosts gain from 20 to 200).

Assessment

What is the gain of the LM386 in its basic configuration vs. high-gain configuration? What type of audio source requires the high-gain configuration and why?