Let's build an audio amplifier from LM386
In this post, we’ll build a great sounding audio amplifier with the LM386 Low Voltage Audio Power Amplifier IC. I built almost a dozen different audio amplifier circuits with the LM386 but most of them produced way too much noise, popping, and other interference. Finally I found one that sounds great. Granted, this is not a “minimal components” audio amplifier. There are lots of extra capacitors added to reduce the noise, and I’ve added a bass boost control as well to make it sound even better. Before we start building, it may be helpful to get a little background information…
The LM386 is quite a versatile chip. Only a couple resistors and capacitors are needed to make a simple audio amplifier. The chip has functions for gain control and bass boost, and it can also be turned into an oscillator capable of outputting sine waves or square waves.
The LM386 is a type of operational amplifier (Op-Amp). Operational amplifiers have a basic task. They take an input potential (voltage) and produce an output potential that is tens, hundreds, or thousands of times the magnitude of the input potential. In this circuit, the LM386 takes an audio input signal and increases its potential anywhere from 20 to 200 times. That amplification is what is known as the voltage gain.
GAIN VS VOLUME
After you build this amplifier and play with the volume and gain controls, you will notice that both appear to raise or lower the intensity of sound coming out of the speaker. So what is the difference then? Gain is the amplification of the input potential. It is a characteristic of the amplifier. Volume lets you adjust the sound level within the range of amplification set by the gain. Gain sets the range of possible volume levels. For example, if our gain is set to 20, the range of volume is 0 to 20. If our gain is set to 200, the range of volume is 0 to 200.
The LM386 IC has 8 pins as shown in the diagram below:
(LM386 Pin Diagram)
The main pins to be aware of are pins 2 and 3, the audio signal inputs, and pin 5, the positive audio output signal. Gain control can be achieved by bridging pins 1 and 8 with a 10 μF capacitor. If pins 1 and 8 are not connected, the output gain will be 20. With only a 10 μF capacitor, the gain will be 200. The gain can be adjusted to any value between 20 and 200 by placing a potentiometer in series with the capacitor.
There are three varieties of the LM386, each with different output power ratings:
LM386N-1: 0.325 Watts
LM386N-3: 0.700 Watts
LM386N-4: 1.00 Watts
Here’s a schematic of the internal circuitry of the LM386 for your reference:
(LM386 Internal Circuit)