This post shows you how to build a mini amplifier circuit using a common chip called the LM386.
It is cheap, easy to make and can make your music player or speakers much louder.
This amplifier is perfect for small projects and is not powerful enough for huge concerts, but it is a great way to learn about electronics and make your music sound better.
What is a LM386 Audio Amplifier:
The LM386 is a widely used low power audio amplifier integrated circuit IC designed for use in electronic projects where amplification of audio signals is required.
It is commonly employed in small audio applications such as portable audio devices, intercoms and hobbyist projects due to its simplicity, affordability and ease of use.
Understanding LM386:
The LM386 is an all in one Class AB Audio Amplifier IC with a legacy spanning decades still widely utilized in computer speakers and portable stereos.
The commonly used 8 pin DIP package encapsulates the LM386 as depicted in the pinout diagram.
Pin Functions and Gain Control:
Examining the pin diagram we observe a basic configuration with minimal external connections.
Pins 1 and 8 serve as Gain Control Pins, defaulting to a gain factor of 20.
Introducing a capacitor between these pins bypasses the internal resistor elevating the gain to 200.
Pins 2 and 3 function as inverting and non inverting inputs, connected internally to an OP AMP.
The audio source whether from a mobile phone, laptop, music player or microphone, connects to the audio input.
Power Supply and Output:
Pins 6 and 4 are the power supply pins accepting a maximum supply of 15V.
In this project, a 12V power supply is employed.
Pin 7 facilitates decoupling requiring a capacitor connection to the ground.
Pin 5 represents the output, necessitating proper filtering before connecting to a speaker to prevent potential damage due to DC signals.
Applications of LM386:
The LM386 finds widespread use in the audio domain serving as a crucial component in portable speakers, music players, laptop speakers, TV sound systems, ultrasonic drivers, voice recording from microphones, battery operated small speakers and FM radio devices.
Its versatility makes it a go to choice for various audio applications.
Circuit Working:
Parts List:
| Category | Description | Quantity |
|---|---|---|
| Resistor | 10Ω 1/4 W CFR | 1 |
| Potentiometer | 10K | 1 |
| Capacitors | Ceramic 0.047µF | 1 |
| Electrolytic 10µF 25V | 2 | |
| Electrolytic 1000µF 25V | 1 | |
| Semiconductor | IC LM386 | 1 |
| Other | Speaker 8Ω | 1 |
The LM386 Audio Amplifier circuit works by taking a low power audio input signal and amplifying it to a level suitable for driving a speaker.
The LM386 operates on a low voltage power supply typically ranging from 4V to 15V.
In this circuit, a 12V power supply is used.
Pins 6 (V+) and 4 (V-) are connected to the positive and ground respectively, providing power to the IC.
Pins 1 gain 1 and 8 gain 2 control the gain of the amplifier.
By default, the gain is set to 20.
However, a capacitor between these pins can bypass the internal resistor and increase the gain to 200.
In the provided circuit, a 10μF capacitor is used for this purpose.
Audio Input:
The audio input is fed into pin 2 inverting Input and 3 non Inverting Input.
The inverting input pin 2 is grounded, and the non inverting input pin 3 is connected to the tip of a 3.5mm audio jack.
The sleeve of the audio jack is connected to the ground.
Output Stage:
Pin 5 output is connected to a 0.047μF capacitor serving as a coupling capacitor.
This capacitor blocks any DC component and allows only the AC audio signal to pass through.
The other end of this capacitor is connected to the positive supply.
Pin 5 is also connected to the positive leg of the speaker.
The negative leg of the speaker is connected to the ground.
This setup allows the amplified audio signal to drive the speaker.
Bypass Capacitor:
Pin 7 bypass is connected to a 250μF capacitor.
This capacitor is a decoupling capacitor that helps stabilize the operation of the IC by filtering out noise and fluctuations from the power supply.
Circuit Construction:
How to build an LM386 Audio Amplifier Circuit steps mentioned below:
LM386 Pin Connections
- Place the LM386 IC on the PCB.
- Connect Pin 4 to the ground.
- Connect Pin 6 to the positive supply using a 12V power supply.
Gain Control
- Connect pin 1 and pin 8 with a 10k resistor.
- Connect a 10μF electrolytic capacitor between pins 1 and 8 to set the gain to 20.
- Optionally, connect a potentiometer between pins 1 and 8 for adjustable gain.
Audio Input
- Connect pin 2 to the ground.
- Connect pin 3 to the 3.5mm audio jacks tip.
- Connect the sleeve of the audio jack to the ground.
Power Supply
- Connect pin 6 to the positive rail using the 12V power supply.
- Connect pin 4 to the ground.
Output Stage
- Connect pin 5 to a 0.047μF ceramic capacitor.
- Connect the other end of the capacitor to the positive supply.
- Connect pin 5 to the positive leg of the speaker.
- Connect the negative leg of the speaker to the ground.
Bypass Capacitor
- Connect pin 7 to a 250μF electrolytic capacitor.
- Connect the other end of the capacitor to the ground.
Formulas and Considerations:
Gain Calculation: By connecting a 10µF electrolytic across pins 1 and 8, the circuits actual gain can be increased to 200.
This occurs because the capacitor correctly shorts out the 1.35K resistor that is incorporated into the IC.
If pins 1 and 8 are not connected to a capacitor, the amplifiers gain drops to 20.
Filtering Capacitor:
- The 0.047μF capacitor connected to the output helps filter out DC components protecting the speaker.
Decoupling Capacitor:
- The 250μF capacitor at pin 7 ensures stable operation by decoupling the IC from power supply fluctuations.
Conclusion
Follow these process you will have a functional and simple LM386 Audio Amplifier circuit ready for various applications.
Adjust component values based on your specific requirements and experiment with different configurations for optimal performance.
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