I'm still learning digital electronics, and analogue electronics is very much a dark art for me. I have the circuit as shown below, the audio output stage for an 8-bit programmable sound generator. Channels A, B and C are merged into a mono output for the LM386 amplifier to play through a small speaker, but I'm finding that Channel B is much quieter than A and C.

Everything sounds fine through the headphone socket, it's just the amp that seems to be losing Channel B. I'm not sure what's going on, so thought I'd ask for some advice on the circuit - any help would be appreciated!

Schematic of audio output stage

  • \$\begingroup\$ since A and B are perfectly symmetric (at least as long as the headphones are absent), the only explanation is that channel B is driven differently, or that you made a mistake and one of the components (R5, maybe) is different; but your schematic can't tell us either... \$\endgroup\$ – Marcus Müller Mar 3 at 19:52
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    \$\begingroup\$ another thing might be that if B simply is outputting signals in a different frequency range than A and B, and your LM386 doesn't amplify these as much, you might end up in such a situation. \$\endgroup\$ – Marcus Müller Mar 3 at 19:53
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    \$\begingroup\$ An easy first test would to be swapping what is attached to A and B and seeing whether the quietness follows the "letter" or the signal source. \$\endgroup\$ – Marcus Müller Mar 3 at 19:53
  • \$\begingroup\$ In terms of frequency, I'm able to test this in software by sending the same frequency (and volume) wave to one channel at a time - this is how I know it's Channel B that is coming out much quieter. Swapping A & B is another matter though, as it's all on a PCB and will involve bending pins on the chip to isolate the Channels... :/ \$\endgroup\$ – nockieboy Mar 3 at 21:36

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