35W RMS x 3-Channel Power Amplifier System.

Design Objectives This design is intended to drive the rear (stereo) and center channel speakers for surround-sound applications. This project combined with the 60W+60W power amplifier, which will drive the main stereo (front) speakers, gives a full 5 channel surround sound systems (Total power = 225W RMS). The power supply circuitry, PCB size and dimension should be designed to match nicely with the 60W+60W power amplifier so that later they may be nicely cased togather.

System Operation & Description The LM4781 3-channel audio power amplifier are configured as non-inverting amplifier which has a gain of 20V/V per channel, which is high enough to maintain stability and not too high until increasing the noise and THD+N performance. The inputs are taken from the RCA jacks which then feed to three high quality 1uF metallized polyester capacifor with 63V rating. The outputs are wired to the speaker terminals directly.

The schematic diagram is taken straight out from the National Semiconductor's referance PCB design schematic. However I have omitted the muting switch and replaced it with the soft start circuit, as explaned in the LM4781 datasheet. I have also added the L//R network (L=0.7uH, R=10 ohms 2W) at all the outputs.

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