This is a 4 channel amplifier circuit build based two IC LM1877N. A LM1877 can be used for a stereo amplifier. The circuit ideally suited for use with quadraphonic equipment such as a Sound Blaster Live card. There is no volume control in this circuit, audio levels being directly controlled from the sound card itself.
D1-D4: 1N4001 (4)
C1,C20: 1000u CAP (2)
C2,C11: 47u CAP (2)
C3,C5,C7,C8,C12,C14,C16,C17,C21,C22: 0.1u CAP (10)
C4,C6,C13,C15: 10u CAP (4)
C9,C10,C18,C19: 2200u CAP (4)
R1,R4,R9,R12: 1M RESISTOR (4)
R2,R6,R10,R14: 100k RESISTOR (4)
R3,R5,R11,R13: 1k RESISTOR (4)
R7,R8,R15,R16: 2R7 RESISTOR (4)
IC1: 7812 (1)
IC2,IC3: LM1877N (2)
SPK1,SPK2,SPK3,SPK4: 8R 2 Watt speakers (4)
The overall gain is controlled by the ratio R14/R13 and R6/R5. Used by small Hi-Fi speakers, the volume was too loud for small room so you may reduce R14 and R6 to 33k. The Zobel network formed by R7, C7, R8, C8, R15, C16, R16, C17 prevents instability which can happen with long speaker wires. The input impedance is high, 1M and if very long input cables are present could pick up noise. Screened cable should be used, in my case I used 10k resistors between points A & C, B & C, D & F, E & F. This provides a DC path to ground and higher noise immunity. If instability does occur, then you will notice sound distortion and the LM1877N will become hot to touch.
4 Channel Amplifier circuit source: zen22142.zen.co.uk
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