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What categories of op amp would be best for a driver circuit that drives 8 ohm DC speakers at low frequencies (under 500 Hz) but is battery powered (no more than 6V DC)? The waveform doesn't have to be smooth so even a class D would be fine. 1W power draw is fine.

Should I be looking for a high impedance / high gain or some other features?

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  • \$\begingroup\$ How much power do you need from the speaker? \$\endgroup\$ – WhatRoughBeast Mar 1 '16 at 1:09
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Check out LM386. It is made to be used as an amplifier. Op amp won't do it or it won't be good.

It's an old chip that's really not that great but will work just fine. It's only 1/2W though but I think there are versions of equally or more than 1W. Also it is really easy to build.

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For a battery powered application you definitely should use a class-D amplifier and not an opamp. For 6V you can have a maximum power of around 2W. First things to check are SNR (> 90dB) and THD (< 0.1% or 60dB, audio freaks would need 20dB on top of that).

A classical class-D amplifier requires an output filter, but "filterless" class-D amplifiers are available that use a different modulation scheme so that you can use them without a filter.

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  • \$\begingroup\$ Wouldn't he want SNR > 96dB? That way he could at least listen to CD quality audio. \$\endgroup\$ – Dave Mar 1 '16 at 3:24
  • \$\begingroup\$ 16 bit would be 98dB. For a portable device 90dB is ok.The driver should be for frequencies up to 500Hz, which is not actually CD quality. \$\endgroup\$ – Mario Mar 1 '16 at 5:44

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