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LM386 Amplifier Circuit – Working Specifications Explained

LM386 Amplifier Circuit – Working Specifications Explained

The IC LM386 is a 8-pin tiny power amplifier chip, specially made for operating under relatively low voltage parameters, yet provide considerable amplification.

IC LM386 amplifier circuit becomes suitable for applying in small low power audio gadgets like in FM radios, door bells, telephones etc.

Let's begin the IC LM386 amplifier explanation by studying its absolute maximum ratings first, meaning the parameters which should not be exceeded while using this IC in any circuit:

Technical Specifications of IC LM386

  1. Supply Voltage: 4V to Max. 15V (Typical)
  2. Input Voltage: +/- 0.4 volts
  3. Storage Temperature: -65 degrees to +150degrees Celsius
  4. Operating Temperature:  0 to 70 degrees Celsius
  5. Power Output: 1.25 watts
  6. IC manufactured by: National Semiconductor

Internal Schematic

internal schematic  of LM386

How to Control Gain for the IC LM386

In order to make the IC better with its response, its pin#1 and 8 have been attributed with a gain control facility which may be set externally.

Gain simply means the capacity or the amplifying level of the device up to which it is able to amplify the applied input low signal audio input.

When the above pin outs are kept unconnected to anything, the internal 1.35K resistor sets the gain of the IC to 20.

If a capacitor is joined across the above pin outs, the gain is suddenly lifted to 200.

The gain may be simply made adjustable by connecting a pot in series with the above explained capacitor across the pin 1 and 8.

Practical Application Amplifier Circuits Using the IC LM386

The following figure shows a typical IC LM386 amplifier circuit having the bare minimum number of components required to make the IC operate at its internally set level of gain 20.

The speaker used is a 2 watt, 8 Ohms type.

The input at Vin may be fed from any audio source such as a cell phone headphone socket, a CD/DVD player RCA L or R socket or any other similar source.

The pin Vs should be connected to +12V DC supply from an AC DC adapter or a home made transformer/bridge power supply unit.

Pin #4 should be connected to ground or the negative of the power supply.

The earth wire or the negative wire from the input audio source should also be connected to the above negative of the power supply.

The input pin#2 goes to a 10K pot which becomes the volume control, one of its end terminals is picked for receiving the input signal while the other end is connected to ground, the center one goes to the hot end of the IC.

The speaker is connected to in #8 via a high value blocking capacitor, the resistor/capacitor arrangement connected across pin #5 and ground has been included for frequency compensation and to provide greater stability to the circuit.

The next circuit shows a similar design as above, except that its pins 1 and 8 have been connected to a capacitor of 10uF, which as explained above helps to pull the gain of the amplifier to 200

MIC amplifier circuit using LM386 IC

The following image shows how the above explained LM386 may be applied for achieving a simple yet powerful microphone amplifier circuit as shown below


About the Author

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials. If you have any circuit related query, you may interact through comments, I'll be most happy to help!

24 thoughts on “LM386 Amplifier Circuit – Working Specifications Explained”

  1. respected sir,
    though i can vary the gain of amplifier by varying the resistance and capacitor value between pin 1 to 8, i didn’t have an idea how actually we are getting the value of resistor and the capacitor. so if anyone can help me please..

    • Hi Tshering, referring to the internal layout of the IC, it seems the (-)input side acts like a constant current source, and this current is replicated at the (+)input side transistors through current mirror circuit.
      The addition of the capacitor allows more voltage to enter through output feedback loop to the (-)input side stage causing more current drive for the (+)input side transistor stage which in turn causes the output to become more powerful.

    • Thank you, glad you liked it, you can simply replace the shown speaker with a headphone, just make sure to reduce the volume control suitably so that the input power does not exceed the headphone specs.

  2. Good write up on the LM 386. One question. Can I use a transformer with the secondary connected to inputs 2 and 3 as an input device. If so could I use an 8 Ohm primary to 1300 Ohm secondary and get some extra gain?
    Thank you.

    • Thanks Hans, I don’t think that would work, because the input of the amp is already is too sensitive and set at high gain, therefore adding more voltage at the input side would result in distortion at the output side.

      • I do not plan to connect pins 1 and 8 with a cap, I just wish to get rid of common mode noise. As alternative could I use a 600 Ohm:600 Ohm audio transformer connected with say 10 uF caps to 2 and 3?

        • OK, so you intend to transfer only the differential value to the amp and eliminate common mode noise, in that case you can try using a trafo at the input

  3. Hello Sir please provide the simple mic amplifier circuit diagram and how to connect it for la 4440 audio circuit board
    Thank you

  4. Hi bro, i want to increase the outpt of LM 386 to around 5W using either Transistors or Mosfets so do have any idea how to configure the driver stage using these ????

    • sorry Bro, I tried but could not find any technically correct LM386 power booster circuit, most of the ideas are based on opamp instead of LM386…

  5. Irshad, if you force the IC to work above it's specified rating then the output will distort.

    so you will need to keep the input music only upto that level which does not exceed the amps max handling capacity.

  6. Sir, i made the circuit with 5volt power from usb port. i had no 0.1uf capacitor i used 10uf capacitor. sound is very good, when i loud the sound, The speaker's voice was burst۔ what is the solution for this????? Sound should be clear on loudness.

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