LM1877 Dual Audio Amplifier

[andrew.grimm3]

I need help with a project building a 2 ch audio amplifier using the LM1877 IC. It needs to drive to (2) 8 ohm speakers and (1) 8 ohm sub woofer. The requirements are to be single supply operation, individual volume controls for the left, right and bass signals. It must be driven from a source of 0.250Volts peak, and source impedance of 1.0k ohm.

 

[audioguru]

I need help....

You need 3 separate channels. But the LM1877 has only 2 channels. What amplifier will you use for the 3rd channel (for the sub-woofer)?
What help do you need? Its datasheet explains and shows how to use it.

 

[andrew.grimm3]

Well I have to use the same LM1877 as the 3rd channel also. What I'm unsure of is how to connect both IC's together.

 

[audioguru]

The LM1877 has very low output power. The sub-woofer will be a just a faint sound and might not be heard.

You don't connect the ICs together, they are separate but the sub-woofer amplifier's input has a 10k resistor from the left channel source and another 10k resistor from the right channel source. The two resistors mix the stereo channels into mono for the sub-woofer.

Usually there is an active crossover circuit that stops high frequencies from going to the sub-woofer amplifier and stops low frequencies from going to the stereo amplifier.