I am going to use AVR's PWM output signal to pass through a low pass filter (maybe plus an amplifier). I found the speaker has a quite low resistance (8 ohms). I tried to simulate my schematic on Orcad, obtaining very a low voltage signal on speaker in (mV). I think that is the problem of this load resistance (I simply put the load resistance across output terminals). But I am not sure how to deal with that. Hope someone can help. Thanks in advance. The same problem occurs when I tried using single simple pole low pass filter. Looking forward to hear your suggestions.

  • \$\begingroup\$ Speaker rate power is 1w. \$\endgroup\$
    – yzhu12
    Mar 2, 2013 at 13:17
  • \$\begingroup\$ Do you have a circuit diagram? Als you can edit your question, no need to add comments for additional information. \$\endgroup\$
    – jippie
    Mar 2, 2013 at 13:54
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    \$\begingroup\$ You need something with power gain between the digital PWM output and the speaker. Think about it. 5 V accross a 8 Ohm load will draw 625 mA. Can your PWM output source that? I didn't think so. \$\endgroup\$ Mar 2, 2013 at 14:55
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    \$\begingroup\$ @OlinLathrop That tone is unnecessary. The path is always clearer if you have traveled it before. \$\endgroup\$
    – W5VO
    Mar 2, 2013 at 20:36

1 Answer 1


Your speaker rated at 1W will require an amplifier circuit to be placed between the DAC / filter circuit and the speaker. There are numerous solutions to provide for this amplifier function including discrete circuits, IC circuits and single chip amplifier modules. You could build up a circuit using a chip amplifier such as an LM386 or you could check online sources to get a low cost ready-made circuit module. Sellers on eBay are making an assortment of modules available such as this example:

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  • \$\begingroup\$ I highly recommend the TDA7056B, it's the best chip-amp I've ever found. \$\endgroup\$
    – krs013
    May 12, 2013 at 3:26

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