LM386 speaker amplifier
The LM386 is a whole power amplifier in eight pins: input on pin 3, speaker on pin 5 through a big capacitor, and a fixed gain of 20 that a 10 µF capacitor across pins 1–8 raises to 200. The 10 Ω + 47 nF Zobel network stops it oscillating with the speaker’s coil.
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How it works
Pins 1–8 open: gain 20 (26 dB). 10 µF across them: gain ≈ 200 (46 dB; 1 + 28.5 kΩ ÷ 150 Ω ≈ 191 in this model).
Output 100 mV p-p in, about 2 V p-p out; into 8 Ω that is 62 mW.
Try it on the bench
- Turn the volume pot down: the output follows.
- Raise V_in to 0.5 V peak with gain 200: the output clips at the rails.
Parts on the bench
- Bench power supply
- LM386 audio amp
- AC source
- Potentiometer
- 2 × Electrolytic capacitor
- Speaker
- Resistor
- Film capacitor
In the course
Electronics Technician, module “Op-amps and timers”.