Friday, March 28, 2014

Fun With LM386


Good evening everyone. Hope you guys are having a great time. Now that my system is on a boot time virus scanning process and it will take a long time I guess I can write something on a small amplifier that can be used in many different places like intercom, small amplifier for MP3 player or radio or maybe any similar application.


So this post is about a small amplifier and I am going to use the great LM386 chip for this. So let’s take a look at the IC first and then I will show a few circuit diagrams.





From the diagram you can see it has a pretty straight forward pin out. Just hook up a power supply, give it some input signal and it will provide output. Diagrams are also very easy.  Gain of this IC is internally set to 20 but you can change it to 200 just by adding an extra component. One of the major benefits of this is IC is it requires only a few external component to work.


Advantages:


1. Only a few external components,

2. Operating voltage range is 4V-15V so it can be operated by battery,

3. At no load it draws only 4mA of current (it can be left turned on for long time),

4. It features low distortion.


So first let’s look at a diagram of small audio amplifier.





As you can see in the figure that the diagram is fairly simple. The input 10Kohm variable resistor works as a volume controller. Pin 3 is the non-inverting input, we will input the signal here, pin 2 which is the inverting input, we will just hook it up to the ground directly ( If you have idea on op-amp you should know this). The output is taken from the pin 5 of this IC and we will use either an 8ohm speaker or 16ohm speaker.


Switch 1 is used for controlling the gain, the options are either 20, 50 or 200. A three way selector switch can be used.


When switch 1 is connected through the 10uF capacitor it will give a gain of 200. When it is connected through the 10uf capacitor in series with the 1.2Kohm resistor it will give a gain of 50. And when it will float free it will give a gain of 20.


Switch 2 is used for turning on/off the bass booster.


Bypass capacitor with the pin 7 can be anything from 47uF to 100uF of proper voltage.


Now let’s look at another figure, it can be used in intercom or something similar.





In this figure as you can see the input is taken from a microphone. 22uF capacitor at the input blocks the DC. Same as before 10kohm variable resistor is used for controlling the volume.


Gain controller and bypass capacitor of this circuit is same as before.


As this circuit is targeted for vocal type range so we don’t need a bass booster on this.


The switch 1 here is of press and hold type, you have to press and hold the button to keep the circuit running.  It is because we don’t want to run the circuit all the time.


So that was all about the small amplifier with LM386 IC.


Note:


1. If you want to learn more about this circuit you can take a look at its datasheet here.

2. Use capacitors with voltage rating a bit higher than the supply voltage.

3. High quality images uploaded, open in new tab to see the full sized image.
4. LM386 can deliver up to 1W.

As this circuit consumes a small amount of current you can easily use a 9V 6F22 battery with it.

Hope you have enjoyed reading this post and I guess now you can make it by yourself. Happy experimenting.
 

To read my other posts, see the index.

To see a power supply diagram for this one click here.

2 comments:

  1. Hello May I ask a question?
    for my project , Is it possible that the input of amplifier is contain 220 volt ac and the output of it is 3 volt using multitester, can you help for the schematic diagram,, can you help for what is the best thing i can do with my project?
    thanks send me an email :))

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    Replies
    1. I'm sorry I somehow missed your comment and I don't get the question either. LM386's max input voltage is about 12V/18V, you can't use more than that, so you can just make a small power supply that will convert the 220V ac mains to any of these voltages.

      or did u mean the input signal? obviously using 220V ac input signal will just blow up the IC!

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