LM386 audio amplifier not amplifying
The LM386 amplifier's inputs are an internally biased differential pair, with common mode input range extending to the indicated ground, Vee, or actually 0.4 Volts below ground.
In order to not disturb this internal biasing, the input signal must be capacitively coupled (or perfectly ground-referenced) - a capacitor in series on the input line is needed.
Next, for a voltage gain of 200, the input signal peak to peak needs to be under 1/200 of the output voltage range of the amp. While I could not find this specified in a quick scan of the datasheet, if we assume 7 volts output voltage range with a 9 Volt supply, the input signal needs to be under 35 mV peak to peak, to avoid clipping the signal. Clipping would result in mild to severe distortion of the output - though this does not explain the complete lack of signal you find on output.
If the incoming signal is higher than this 35 mV P-P, a potentiometer as an attenuator on the input is suggested.
Once these fixes are done, please revert with results, so the answer can be added to if needed.
A LM386 amplifier may behave quite erratically on a breadboard. Here are some ideas that may help you:
- Start out with 20x amplification, i.e. without the capacitor between pin 1 and pin 8. Once you get proper sound at the output, you can always pump up the gain
- Add a 10uF capacitor between pin 7 ("Bypass") and ground. The capacitor's negative lead is towards ground. "A small electrolytic or tantalum cap of a few uF from pin 7 to ground will isolate the high gain input stage of the LM386 from power supply noise, hum, transients, etc." (source)
- Add a 100uF capacitor across the power supply rails, in addition to the 100nF capacitor you have. Some extra filtering never hurts
- Keep all components as close to the LM386 chip as possible
- Keep the input path as short as possible, to avoid external interferences