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I built a 2.1 subwoofer circuit. The schematic is below. The problem is the sound is low volume. It should be louder than this. I want to confirm the coupling capacitor values are ok in every stage.

The main chip amplifier is TDA7377. It is configured as a stereo bridge.

Note: The diagram shows only a single channel & a subwoofer filter.

enter image description here

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    \$\begingroup\$ What's the input impedance of the stage following your preamp (the one marked "To AMP Sub")? If it's low enough, C7 could be your problem. \$\endgroup\$
    – TimWescott
    Nov 5, 2020 at 17:18
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    \$\begingroup\$ And is the gain just too low overall, or is it a frequency-dependent thing? \$\endgroup\$
    – TimWescott
    Nov 5, 2020 at 17:18
  • \$\begingroup\$ Thanks.The datasheet of TDA7377 shows 15Kohms input impedance in bridge mode. (sub out following). And 30Kohms single ended ( sattelites following). \$\endgroup\$
    – Joseph143
    Nov 5, 2020 at 17:36
  • \$\begingroup\$ Why don't you simulate it. Saying the output is low means nothing. \$\endgroup\$
    – Andy aka
    Nov 5, 2020 at 18:01
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    \$\begingroup\$ The circuit looks fine for the TDA7377, but that output amplifier may be to wimpy. In bridge mode, the TDA7377 can only supply a 15W or so into a 4-ohm load with a 12V supply. Not much for a subwoofer. \$\endgroup\$
    – John Birckhead
    Nov 5, 2020 at 20:08

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