electronics-amplifier tutorial

This audio power amplifier project is based almost directly on the "typical application" circuit in the National Semiconductor specification sheet. As it turns out, the typical application circuit is not bad - I would go so far as to say hi-fi in the audiophile sense? Perhaps - with caveats. It has good noise and distortion figures, and is remarkably simple to build if you have the PCB.

Amplifier circuit scheme below shows the original Schematic as shown when this project was originally published. It is almost the same as in the application note, polyester bypass capacitors have been added, and the mute circuit has been disabled

Skema Rangkaian 56 Watt audio Amplifier IC lm3876 atau 3886

Voltage gain is 27dB as shown, but this can be changed by using a different value resistors for the feedback path (R3, currently 22k, between pins 3 and 9). The inductor consists of 10 turns of 0.4mm enamelled copper wire, wound around the body of the 10 Ohm resistor. The insulation must be scraped off each end and the wire is soldered to the ends of the resistor.

The 10 Ohm and 2.7 Ohm resistors must be 1 Watt types, and all others should be 1% metal film. All electrolytic capacitors should be rated at 50V if at all possible, and the 100nF (0.1uF) caps for the supplies should be as close as possible to the IC to prevent oscillation.

The supply voltage should be about + / - 35 Volts at full load, which will let this little guy provide a maximum of 56 Watts (rated minimum output at 25 degrees C). To enable maximum power, it is important to get the lowest possible case to heatsink thermal resistance. This will be Achieved by mounting with no insulating mica washer, but be warned that the heatsink will be at the-ve supply voltage and will have to be insulated from the chassis.

Layout IC lm3876/lm3886