A common chip known as the LM386 is used in this post to show how to construct a circuit for a small amplifier.
It is low cost, easy to build and can boost the volume on once speakers or music player.
Though it is less strong enough for massive shows but this amplifier is ideal for little projects and is a fantastic way to learn about electronics and improve the sound of music.
What is a LM386 Audio Amplifier:
The LM386 is a widely used in low power audio amplifier integrated circuit designed for use in electronic projects where amplification of audio signals is required.
It is commonly used in small audio applications such as portable audio devices, intercoms and hobbyist projects due to its simplicity, affordability and ease of use.
Understanding LM386:
With a decades long history the LM386 is a multipurpose Class AB Audio Amplifier IC that is still frequently used in portable stereos and computer speakers.
As shown in the pinout diagram the LM386 is enclosed in the widely used 8 pin DIP packaging.
Pin Functions and Gain Control:
When we look at the pin diagram we see a simple design with few external connections.
The gain factor of 20 is the standard value for the gain control pins which are pins 1 and 8.
Bypassing the inbuilt resistor and connecting a capacitor between these pins the gain is increased to 200.
An Op amp connects directly to pins 2 and 3 which act as inverting and non-inverting inputs etc.
The audio input is connected to the audio source which could be a microphone, laptop, music player or cell phone.
Power Supply and Output:
The power supply pins that can receive a maximum supply of 15V are pins 6 and 4.
A 12V power supply is used in this project.
Pin 7 makes decoupling simpler however it requires a capacitor to be connected to ground.
The output is represented by pin 5 which needs to be properly controlled before being connected to a speaker in order to guard against possible harm from DC signals.
Applications of LM386:
In the audio industry the IC LM386 is widely used as an essential part in portable speakers, music players, laptop speakers, TV sound systems, ultrasonic drivers, microphone voice recording, battery operated compact speakers and FM radios.
Because of its adaptability it is the popular choice in a wide range of 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 |
| Speaker 8Ω | 1 |
The circuit for the LM386 Audio Amplifier boosts a low power audio input signal to a level that can power a speaker.
Low voltage power supplies usually between 4 and 15 volts are used to power the LM386.
The power supply in this circuit is 12V.
To supply power to the IC pins 6 (V+) and 4 (V-) are connected to the positive and ground etc.
The amplifiers gain is controlled by pins 1 gain 1 and 8 gain 2.
The gain is generally set to 20.
The gain can be increased to 200 by bypassing the inbuilt resistor and using a capacitor between these pins.
A 10μF capacitor performs this function in the circuit that is provided.
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 terminal of the speaker.
The negative terminal of the speaker is connected to the ground.
The speaker can be driven by the amplified audio signal because to this setup.
Bypass Capacitor:
A capacitor of 250μF is connected to pin 7 bypass.
This capacitor which is a decoupling capacitor filters out noise and fluctuations from the power source to help regulate the ICs performance.
Formulas with Calculations:
Below are the for with calculations for Simple LM386 Audio Amplifier Circuit:
Output Capacitor Cut-off Frequency (High-pass filter):
fc = 1 / (2 × π × Rload × C3)
where,
- fc is the cut off frequency in Hz
- Rload is the speaker resistance in ohms which is 8ohms in circuit diagram
- C3 is the output capacitor in farads which is 1000µF
fc = 1 / (2 × π × 8 × 1000 × 10⁻⁶)
= 19.89 Hz
Zobel Network Cut-off Frequency (for stability):
fz = 1 / (2 × π × R1 × C4)
where,
- fz is the cut off frequency in Hz
- R1 is the resistor value in ohms which is 10Ω
- C4 is the capacitor value in farads which is 0.047µF
fz = 1 / (2 × π × 10 × 0.047 × 10⁻⁶)
= 338600 Hz (338.6 kHz)
How to Build:
To build an LM386 Audio Amplifier Circuit follow the steps mentioned below:
LM386 Pin Connections
- The LM386 IC should be placed on the PCB.
- Connect Pin 4 to the ground.
- Use a 12V power supply to connect Pin 6 to the positive supply.
Gain Control
- Join pins 1 and 8 together using a 10k resistor.
- To set the gain to 20 connect a 10μF electrolytic capacitor between pins 1 and 8.
- For adjustable gain, you can also connect a potentiometer between pins 1 and 8.
Audio Input
- Connect pin 2 to the ground.
- Wire pin 3 to the tip of the 3.5mm audio jack.
- Put the audio jacks sleeve 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.
- Join pin 5 to the positive terminal of the speaker.
- Connect the negative terminal of the speaker to the ground.
Bypass Capacitor
- Wire pin 7 to a 250μF electrolytic capacitor.
- Join the other end of the capacitor to the ground.
Conclusion
If you follow these steps you will have a simple and working IC LM386 audio amplifier circuit that can be used for numerous of uses.
To get the best performance experiment with different setups and modify component values according to your particular needs.