Audio Power Amplifiers with LM386
The LM386 is a versatile, small power amplifier designed for use in low voltage consumer applications. The gain is internally set to 20 to keep external part count low, but with the addition of an external resistor and capacitor between pins 1-8 the gain can be set to any value from 20 to 200.
The inputs are ground referenced and the output automatically biases to one-half the supply voltage. The quiescent power drain is only 24 milliwatts when operating from a 6 Volt supply, making the LM386 ideal for battery operation.
To make the LM 386 a more versatile amplifier, 2 pins (pin 1 and 8) are provided for gain control. With pins 1 and 8 open the internal 1.35k resistor sets the gain at 20 (26 dB). If a capacitor is placed between pin 1-8, bypassing the built-in 1.35k resistor, the gain will go up to 200.
If a resistor is placed in series with the capacitor, the gain can be set to any value from 20 to 200. Gain control can also be done by capacitively coupling a resistor or FET transistor from pin 1 to the ground.
Operating Supply Voltage (VS) = 4v - 12v Output power (POUT): LM386N-1: 250-325mW @ VS=6V, RL=8Ω, THD=10% LM386N-3: 500-700mW @ VS=9V, RL=8Ω, THD=10% LM386N-4: 700-1000mW @ VS=16V, RL=32Ω, THD=10%
Simple audio amplifier schematics with LM386
Fig 1: LM386 Audio Amplifier with Gain = 20 and minimum part count
Fig 2: LM386 Audio Amplifier with Gain = 200
Fig 3: Audio Amplifier with bass boost
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