I recently got hold of some very cheap speakers but they came with just bare wires and it wasn't something I could just plug into my phone or my computer.
To actually use these speakers, I needed an "audio amplifier" to sit between my audio input source and my speakers. Luckily, creating an audio amplifier isn't too difficult using the right parts.
In this article, I'll be going over how to create a simple class A/B audio amplifier with the LM386 that you can use for various audio projects.
First off you are new to audio electronics, it may not be obvious what an audio amplifier really does.
The role of an audio amplifier is as the name implies - to ampify an input audio signal.
An input audio signal would be the audio signal from your computer, phone, microphone or even an electric guitar.
These input audio signals are usually weak in the range of only a few hundred microwatts (tiny) so if you tried connected this directly to speakers you wouldn't hear very much. This is where an audio amplifier comes in.
By placing an audio amplifer between your audio source and your speakers, you can amplify the original audio source so that it is high enough for hearing in a speaker.
The amount of amplification is known as the the "gain" and you can get various gains dependingon the IC you use.
To create our audio amplifier, we'll be using the LM386, which is a common low voltage audio amplifier.
The LM386 is a great choice if you want to build radios, small guitar amps and other maker electronic projects that use:
The LM386 supplies anywhere from 0.25 to 1 watts of power depending on the model and runs off a minimum voltage supply of 4~5V.
Now 1 watt of power might sound pretty small but I've found that even it's enough to fill the whole room with loud music.
Here are the different specifications of each LM386N models per wikipedia.
| Name | Min V | Max V | Typical Watts |
|---|---|---|---|
| LM386N-1 | 4 | 12 | 325 |
| LM386N-3 | 4 | 12 | 500 |
| LM386N-4 | 5 | 18 | 1000 |
You'll find various configurations of the LM386 but after various experiments, this is the configuration that I have found works best for most cases.
This particular configuration has an internal gain set to 20. C3 capacitor isn't really necessary unless you plan to use higher gains (see below for more on this).
The audio source is up to you but here I'm using a TRRS module since I had bought a bunch in the past but a regular audio jack would also work.
In this configuration, we are combining two stereo audio signals as a single mono and feeding it to the R1 potentiometer which acts a volume control.
If you had two speakers, you could use LM386 amplifiers and feed each stereo audio channel to the left and right speakers.
You can optionally increase the gain by adding a capacitor between PIN1 and PIN8 as shown right.
For example, a 10uF capacitor would result in a gain of 200.
Capacitors C7 and C4 serve as decoupling capacitors to decouple the low and high frequencies of the power supply.
Since a speaker can act as an inductor, C1, C2 and R2 helps to reduce feedback from the speaker itself.
As mentioned above, C3 capacitor is optional and might not be needed unless you are working with higher gains above 20.
Here is a birds-eye view of the circuit above (note that this contains the optional capacitor between PIN1 and PIN8).
In my final version, I created a pcb out of the schematics above, wired up everything and put into a nice 3 printed case.
I'm a senior front-end engineer by day and electronics inventor by night. I setup this site to share my explorations, discoveries and learnings with you.
Feel free to mail me if you have any questions or feedback.
