A linear audio amplifier module that can deliver up to 60W RMS at 0.1% THD into four and eight ohm loads depending on supply voltage. The design of the module is based on an LM3886 integrated power op-amp instead of discreet parts. This module requires a suitable split-rail DC power supply to operate.
The LM3886 is a single power operational amplifier. It is used in the non-inverting configuration in this circuit together with additional supporting components that may be necessary depending on application. These additional components can be omitted during construction if they are found to be superfluous in a particular application. The table below describes the function of each component. Those marked with an asterisk are not strictly required for the circuit to operate as an amplifier.
||Static drain. This is to protect against large voltages from developing across C1 and C2 due to electrostatic discharge. This can happen when the input connections are exposed or touchable.
||This resistor sets the input impedance. This forms a highpass filter with C1 and C2 with a cutoff frequency of 1/(2*pi*R2*(C1+C2)).
||These resistors set the voltage gain of the amplifier. The gain is given by 1 + R5/R3.
||This prevents large currents from flowing into pin 10 of IC1. This can happen when the supply rails to IC1 fall below approximatly 1.5V.
||This limits the current flowing out of pin 8 of IC1. If this current falls below 500uA then the amplifier will be muted.
||This provides a high frequency bypass to suppress any tendencies for the amplifier to oscilate. This can be caused by input-output coupling from long cable runs, etc.
||These protect the amplifier from becoming unstable when driving capacitive loads such as long loudspeaker cables and piezoelectric tweeters. R8 is located inside L1. L1 consists of eleven turns of 1mm diameter enamelled copper wire wound on an 8mm former.
||Input coupling capacitors. These provide AC coupling.
||These ensure that the amplifier has unity gain at DC. Plastic film capacitor C3 is to provide a high frequency bypass to non-polarised electrolytic C4 as some electrolytic capacitors can have a diminished high frequency performance.
||This provides high frequency noise suppression.
||C6,C7 and C8,C9 provide high and low frequency local supply decoupling respectively. Note that C8 and C9 are only to provide local decoupling and will not suffice as power supply smoothing capacitors.
||This keeps the amplifier muted until the supply voltages have risen to their nominal values. This prevents output transients at turn-on.