I've built an amplifier with an lm386 but when I connect a speaker (8ohm) to the output I get a very distorted signal. The problem appears only when the speaker is connected. If I connect an external amplifier to the lm386 output, the audio is right. The issue appears also without gain capacitor between pin 1 and 8 and with the most basic configuration from the datasheet (LM386 with Gain = 20, page 8 on TI datasheet)

How is it possible? enter image description here

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    \$\begingroup\$ The schematic shows that the amplifier power supply is 9V/GND, and the incoming AC signal is also referenced to GND. Is that correct? What happens when the AC signal goes below GND? \$\endgroup\$ – scorpdaddy Apr 3 '19 at 19:52
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    \$\begingroup\$ @scorpdaddy: If it were connected like the datasheet says to, then it wouldn't matter about the AC going negative. The LM386 is made to deal with that. The + input actually has DC bias on it. It is not an opamp. \$\endgroup\$ – JRE Apr 3 '19 at 19:58

Compare your circuit with an example from the datasheet:

enter image description here

  1. You have the + input grounded rather than the - input as in the datasheet. The LM386 only works properly when the - is grounded and signal goes in the +. You have the connections to pin 2 and pin 3 swapped.

  2. You have some strange feedback from the output to the gain input. Don't do that. The gain pins should only be connected together (through a capacitor or a capacitor in series with a resistor.) Remove R18 and C9.

The LM386 is not an opamp. It is a power amplifier whose symbol happens to resemble that of an opamp.

It doesn't work like an opamp, and you can't treat it as one.

  • \$\begingroup\$ I used this schematic [link] circuitbasics.com/… Using connection to pin 2 and 3 in the right way the out improve slightly but the distortion remains. The only way I found to have a right output is to swap pin 2/3, remove gain capacitor and bass boost, use a 100k resistor on input and a 4.7k resistor from input to ground. The output is very low in this way. The inexplicable thing is that distortion comes out only when a speaker is connected if the output is connected to another amplifier the sound is correct. \$\endgroup\$ – simone Apr 4 '19 at 15:19

Looks like you are using this circuit:

enter image description here

You should leave pin 8 open in that case, and apply the input signal to pin 3.

If you don't want the bass boost, use one of the other circuits in the datasheet.


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