yellow channel is from lm386 amp 20 times gain
my circuit is from the lm386 datasheet with 16 V source, what i amplify is 40khz arduino pwm output, is there any explanation why this happened, thanks
Electronic – What happened with this LM386 Amplifier Output
lm386pwm
Related Solutions
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.
There is a reason LM386 datasheets include the Zobel network in parallel with the speaker. You built an oscillator and amplifier in one.
simulate this circuit – Schematic created using CircuitLab
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Best Answer
The waveform distinctly shows that the LM386 is not an amplifier with the bandwidth or output slew rate capable of amplifying your input waveform that has basically square edges.
The LM386 is considered to be an audio power amplifier which would mean that it would be typically capable of handling sine wave type audio frequencies from about 100Hz up to about 20kHz in a real application.
The part is speced to have a bandwidth of typically 300KHz when the gain is at its default level of 20. Of course that is for sine wave signals. At the large wave signal you are feeding you will come no where close to that.