Simple audio amplifier with a LM386.

The LM386 chip is a popular little 8 pin chip at the moment. We have a lot of questions how to make a simple amplifier with it. The LM386 does not need a lot of extra components and that's why it is so easy to work with. When you use a 9V battery and a 8 Ohm speaker, the output power (Pout) will be 0,7 Watt.

The LM386 is an analog low voltage power amplifier, specially designed to use in combination with a battery (low current). You can make a headphone amp (for stereo you need two), a small active loudspeaker and lots of other (small, low powered) audio applications. I will show and explain how you can build a mono amplifier on a breadboard and printed circuit board.

1. First start with looking up the datasheet of the LM386. This datasheet is an 'usermanual' for this chip and you will find all relevant information about that chip, including example circuits or so called 'application notes'. The circuit I show here will be the simplest application note.

The circuit only consists of a few components. On the left the audio input. This is the source signal (output from an iPod for example). The triangle in the middle is the symbol of the LM386 with it's connections. On the right side the speaker and an output filter (avoiding oscillation) and a big capacitor.
The next step is to create the circuit on the breadboard and make it work. Make the connections step by step. Start with the power supply (9V dc battery).

This setup shows the complete circuit. There's no input potentiometer connected on this photo, but the audio is directly connected to the input pin (3) of the chip. I will add the potmeter on the printed circuit board later on. The breadboard setup is to check whether the basic setup is functional and also to get familiar with the circuit.

When the amplifier is fully functional on your breadboard, it's time to make the printed circuit board. This type of (experimental) board has all separate soldering pads on the backside. All the connections still have to be made by you.

I start with cutting out a small piece of experimental printed circuit board and I will use a socket for the chip. This socket makes it easier to replace the chip in case of damage. Believe me, it will happen ;-)

 

All the connection are to be made on the backside of the board. On this side (the soldering side) you can solder the components to the board. At this photo only the socket itself is soldered. Also be aware of the fact that these photo's are mirrored!
Place the components on the top side (also called component side) and try to find the most practical location on the board. This can take some time to get it right.
Cut the long wires on the back.

Use normal (iron) wire to make the connections between the points that have to be connected.

Note that I used thicker wire for the GND connections. In this way you alway recognise which of the wires is ground.

I use small male headers for the connections of the wires (9V + and -, audio input, speaker output and potentiometer). It's more clear to have the wires connected to the top side of the board. It's more transparant and easier to measure and access the circuit.
Complete all the connections on the backside (soldering side).
Solder the wires to the male headers.

Connect the battery, speaker and audio and check if all is working as expected.  Don't forget to document the project and enjoy the 'sound' ;-)

 

If the amplifier is not working:
- check the position of the chip (pin 1)
- check all the connections again
- check the polarity of the capacitors
- check the battery. Is it still 9V?
- Are you sure you have audio signal at the input?
- Do you hear 'sissing or humming' sound on from the speaker (this is a good thing, it means it works).

Try to check the circuit step by step and make it work! ;-)
Good-luck!

2015-06-01 13:16:50
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