Adding a Push-Pull Output Stage to a LM386 Audio Amplifier
The above amplifier takes the classical and inexpensive LM386 audio amplifier and adds a pull-pull output stage for greater power. This amplifier is used in the above video. The output is several watts as opposed to 400 mW. Do not exceed 14-15 volts DC input.
For Q1 and Q2 use TIP31 and TIP32 or TIP41 and TIP42 or any suitable matched PNP/NPN pair. In my case I used a transistor checker to match the gain on two TO-220 power transistors.
Note this design is also more sensitive than everyday computer speakers. The LM386 is available at Radio Shack.
To make the LM386 an even more versatile amplifier, two pins (1 and 8) are provided for gain control. With pins 1 and 8 open the 1.35k resistor sets the gain at 20 (26dB). If a capacitor is put from pin 1 to 8, bypassing the 1.35k resistor, the gain will go up to 200 (46dB). One can always put an on/off switch between pin 1 and the capacitor if less gain is needed. My unit is used as a utility amplifier for various radio and computer projects.
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 from pin 1 to ground.
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