LM1875 25W Hi-Fi Audio Amplifier Circuit Schematic

LM1875 25W Hi-Fi Audio Amplifier Circuit Schematic a high fidelity amplifier module using the National Semiconductor LM1875 IC
LM1875 25W Hi-Fi Audio Amplifier Circuit Schematic

BOM's

  • R1 = 1K
  • R2 = 1M
  • R3 = 22K
  • R4 = 10K
  • R5 = 180K
  • R6 = 1R
  • C2, C6 = 100nF
  • C4 = 0.22uF
  • C1 = 1uF 50V
  • C3 = 22uF 63V
  • C7, C5 = 220uF 50V
  • IC1 = LM1875
  • FS1, FS2 = 2A
The input signal is coupled via R1 and C1 to the noninverting input (pin 1) of the IC. The closed loop gain of the amplifier is set to 19 by resistors R5 (180K) and R4 (10K). R4 and C3 (22uF) set the lower 3dB frequency point to 7Hz.

The output appears at pin 4 of the IC and drives a loudspeaker directly. Long speaker leads can produce enough capacitance to drive amplifiers into VHF oscillation. Resistor R6 (1W) and capacitor C4 (0.22uF) help prevent this. They are connected across the output and form a Zobel network which provides high-frequency stability when driving capacitive loads.

The power supply is connected via 2A fuses to protect against any external shorts to ground. Capacitors C5 and C7 provide further on-board supply decoupling.

This circuit will deliver 25W RMS into 8 ohms @ 1% THD.
LM1875 25W Hi-Fi Audio Amplifier Circuit Schematic