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I am using the output of usb sound card as an input to PAM8403 ic with specs from datasheet. However i am using 4 ohm 0.5 W speaker. So i have tried testing with that and it works but sometimes with time volume starts getting slow.

Today i tried to put volume of pc at 72/100 to check the output. It turns out that after some time speaker starts getting heated and then burns in the center and back.

I am using same circuit as datasheet but low wattage speaker. As I have bulk of those speakers with me as well as PAM8403 IC, I would like to know if there is a way i can make these speakers work with the Amplifier...

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  • \$\begingroup\$ Today i tried to put volume of pc at 72/100 to check the output That doesn't mean anything if you play an mp3 file containing silence. Probably you're expecting way too much volume from those poor 0.5 W speakers. For more volume and better power handling, connect many speakers in series/parallel and mount them in a box. \$\endgroup\$
    – Bimpelrekkie
    Commented Sep 26, 2019 at 13:13
  • \$\begingroup\$ They did play well... It's just that at that volume (of song), the speakers started burning hot, so that one of internal wire melted and thats what i want to know why and if i can control that limit amplifier somehow... I have bulk of those to be used in confined spaced box... If possible \$\endgroup\$
    – Akshit
    Commented Sep 26, 2019 at 13:18
  • \$\begingroup\$ "is a way i can make these speakers work with the Amplifier" - Yes, there is - and you've already done it. Your problem is that you're over-driving the speakers and the solution is "don't do that". \$\endgroup\$
    – brhans
    Commented Sep 26, 2019 at 14:37

2 Answers 2

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The important battery voltage is not mentioned. It and the speaker impedance determine the maximum output power. With a 2.5V supply the output power is shown in a graph on the datasheet to be 0.5W into 4 ohms at low distortion or 0.8W with high distortion. With 2.5V supply, the maximum output into an 8 ohm speaker is only 0.3W with low distortion or 0.4W with high distortion.

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Besides distorting rather badly at full volume (10% distortion), four ohm speakers thermally stress this little chip.
Consider that power transfer efficiency is about 82% with 4-ohm load. Data sheet doesn't make clear if this is one channel operating or both channels operating. When 3W is delivered to a 4-ohm speaker, the chip must dissipate 0.54W. In addition, quiescent power is 0.016A * 5v = .08W
Thermal resistance (junction-to-air) is 110 degrees per watt. That means the chip junction is about 60 degrees above ambient temperature. If both channels deliver three watts, the chip is over-stressed.

When chip operation degrades after awhile, thermal stress should come to mind as a possible cause. Two approaches might be taken:

  • add a heat sink to the chip to dissipate heat.
  • increase load resistance on each channel.

Edit:
0.5W speakers driven by an amplifier that can deliver 3W invites speaker destruction.

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  • \$\begingroup\$ I have tried overloading the amplifier to 75% volume for experiment. My findings were that chip didn't heat up much but speaker did. And wire inside speaker melted in the end... I will try adding load resistor in few ohms. Can you recommend a value? \$\endgroup\$
    – Akshit
    Commented Sep 26, 2019 at 13:34
  • \$\begingroup\$ Your 0.5W speakers can't handle 3W power that this chip can deliver. You might try two speakers in series. That's 4 speakers for 2 channels. \$\endgroup\$
    – glen_geek
    Commented Sep 26, 2019 at 13:37
  • \$\begingroup\$ Can i simply add a series resistor? About few 10 ohms around? \$\endgroup\$
    – Akshit
    Commented Sep 26, 2019 at 13:40
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    \$\begingroup\$ Adding series R is a poor engineering solution. Substituting 3W speakers would be better. \$\endgroup\$
    – glen_geek
    Commented Sep 26, 2019 at 13:49
  • \$\begingroup\$ I have loads of speaker which i have to put to use... Can i use at lower volume? I also try replacing with some 2w speaker. Also those only can fit in body. Can i use them? \$\endgroup\$
    – Akshit
    Commented Sep 26, 2019 at 13:51

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