Electronic – Is a low load resistor a big problem in low pass filter and amplifier circuit

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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.

Best Answer

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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