I am trying to diagnose why my LM386 (250mW version) audio amplifier is crackling when the volume is more than a few mV. I created the circuit according to the diagram on the datasheet with pin 7 and 8 floating and no variable resistor (signal from 3.5mm mono cable directly into pin 3). I did the following:

  • Used a "star grounding pattern" with all grounds connected to a common point next to the ground pin of the chip
  • Used a shielded 3.5mm mono cable
  • Tried adding a 250uF and 1000uF power supply decoupling capacitor
  • Tried changing the 250uF decoupling output capacitor to 1000uF
  • Tried a different speaker (4 ohm and 8 ohm)
  • Tried a different power supply
  • Tried removing the Zobel RC Filter
  • Power Supply is 12V / 120W

None of the above made a difference. Only when playing audio at very low (almost inaudible) volume does the crackling disappear. This is the output from the speaker:

enter image description here

This is the prototyped board:

enter image description here

enter image description here

  • \$\begingroup\$ What's your supply voltage? How much current can your power supply offer? \$\endgroup\$ Commented Sep 12, 2021 at 22:48
  • 1
    \$\begingroup\$ Ceramic decoupling cap? \$\endgroup\$
    – Mattman944
    Commented Sep 12, 2021 at 23:09
  • \$\begingroup\$ @MarcusMüller 12V, the SMPS can supply 120W. \$\endgroup\$
    – tgun926
    Commented Sep 12, 2021 at 23:17
  • \$\begingroup\$ @Mattman944 electrolytic for both. Only the Zobel capacitor is ceramic \$\endgroup\$
    – tgun926
    Commented Sep 12, 2021 at 23:18
  • 1
    \$\begingroup\$ Looks like there might be an unintended stray copper strand (i.e. a short) between pin 6 (Vs) and 7 (bypass), but it’s hard to make out clearly. \$\endgroup\$
    – StarCat
    Commented Sep 13, 2021 at 6:10

1 Answer 1


Place a 47 nF capacitor across the IC's power supply as the spec sheet says, fig. 22.

enter image description here

  • 1
    \$\begingroup\$ The AC coupling input cap Cc shown in this diagram would probably also be a good idea. \$\endgroup\$
    – brhans
    Commented Sep 13, 2021 at 0:08
  • 4
    \$\begingroup\$ The supply bypass capacitor should be placed very close to the chip, directly from pin 6 to pin 4. \$\endgroup\$
    – glen_geek
    Commented Sep 13, 2021 at 0:31

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.