LM386 Audio Amplifier Circuit
Low voltage audio power amplifier with minimal external components
Circuit Description
The LM386 is a low voltage audio power amplifier designed for use in low power consumer applications. It can deliver up to 325mW with minimal external components and operates from a single supply voltage.
Key Features:
- Low supply voltage: 4V to 12V operation
- High input impedance: 50kΩ typical
- Low distortion: 0.2% THD at 325mW
- Thermal shutdown protection built-in
- Gain adjustable from 20 to 200
Always observe capacitor polarity and use appropriate heat sinking for higher power operation.
Required Components
Components needed to build this amplifier
Step-by-Step Instructions
Insert the 8-pin IC socket into the breadboard or PCB
Connect power supply pins: pin 6 to +9V, pin 4 to ground
Add power supply filtering with 0.1µF capacitor across power pins
Connect input coupling capacitor (C1) to pin 3 through volume control
Wire the volume control potentiometer for input signal adjustment
Connect output coupling capacitor (C2) from pin 5 to speaker
Add speaker protection resistor (R1) in series with speaker
Install the LM386 IC in the socket with correct orientation
Connect audio input jack with proper ground connections
Test with audio source at low volume first
Pin Configuration & Circuit Theory
LM386 Pinout:
Pin 1: Gain Control
Pin 2: Inverting Input (-)
Pin 3: Non-inverting Input (+)
Pin 4: Ground
Pin 5: Output
Pin 6: Supply Voltage (+)
Pin 7: Bypass
Pin 8: Gain Control
Gain Settings:
- • Default gain: 20 (26dB) - pins 1&8 open
- • Maximum gain: 200 (46dB) - 10µF between pins 1&8
- • Custom gain: Use resistor/capacitor network
Design Notes:
- • Input impedance: 50kΩ (high)
- • Output impedance: low (drives 8Ω loads)
- • Bandwidth: DC to 300kHz
- • Quiescent current: 4mA typical
Troubleshooting Guide
No audio output
Check power connections, IC orientation, and input coupling capacitor polarity
Distorted sound
Reduce input level, check power supply voltage, verify coupling capacitor values
Low volume
Check gain setting, verify speaker impedance, ensure proper supply voltage
Oscillation/feedback
Add power supply decoupling, separate input/output wiring, check grounding
Performance Specifications
Applications & Modifications
Common Applications:
- Portable audio devices and small radios
- Intercom systems and telephone amplifiers
- Guitar practice amplifiers and effects
- Audio signal testing and measurement
Circuit Modifications:
- Add tone control with RC networks
- Include LED power indicator circuit
- Add input switching for multiple sources
- Implement automatic gain control (AGC)
Success Criteria: Clear, undistorted audio with good volume range and minimal background noise.