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I'm currently driving a pair of earbuds with this circuit:

enter image description here

P0 is directly connected to a 3.3V microcontroller pin, which is using PWM to drive it.

I "stole" this filter circuit from the upper left corner of this schematic. I modified it slightly, since I am driving stereo headphones from a single mono input.

The problem I'm running into is that the sound is really loud. I would like to add a volume control. I've read through How to make my own volume control for headphones?, but my situation is slightly different:

  • I don't have an amplifier.
  • The signal I'm starting with is 3.3V, rather than 1V.

My questions are:

  • Should I put the potentiometer before or after the filter? Or does it not matter?
  • Should I use a 1K pot, as mentioned in the other question, or does my situation require a different value of pot? More importantly, how do I calculate this value? (The other question doesn't explain how the value 1K was chosen.)

Thanks!

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You can place a 1kOhm potentiometer in series with R1. This will control the current flowing into the 4-8 Ohm speaker load. It will also alter the cut-off frequency of the High-Pass filter, but I think this should not be a problem.

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  • \$\begingroup\$ So to place the potentiometer "in series" with R1, does that mean using just two legs of the potentiometer and leaving the third leg unconnected? (In other words, the potentiometer is functioning as a variable resistor, not as a voltage divider?) \$\endgroup\$ – user31708 Oct 7 '18 at 16:17
  • \$\begingroup\$ Yes, variable resistor is the way to go. \$\endgroup\$ – Stefan Wyss Oct 7 '18 at 17:50

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