20W audio amplifier using LM1875


This is just another 20W audio amplifier circuit , but this time based on the LM1875 audio amplifier IC from National Semiconductors. With a 25V dual power supply LM1875 can deliver 20W of audio power into a 4 ohm speaker. The LM1875 requires very less external components and has very low distortion. The IC is also packed with a lot good features like fast slew rate, wide supply voltage range, high output current, high output voltage swing, thermal protection etc. The IC is available in TO-220 plastic power package and is well suitable for a variety of applications like audio systems, servo amplifiers, home theatre systems etc.

Circuit diagram.


  • Assemble the circuit on a good quality PCB.
  • Use +/-25V DC dual supply for powering the circuit.
  • K1 can be 4 ohm, 20W speaker.
  • A proper heat sink is necessary for the IC.
  • F1 and F2 are 2A fuses.