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For some context, see my earlier question: Ceramic capacitor value for an LM386N project

What I learned is that the 10k potentiometer on pin 3 (Vin) forms a voltage divider. When I carefully dial it, I find a spot where I get clean audio (the 10k pot is then at ~ 500 Ω). This is the same with the ready-made breakout board that I used for comparison.

Now the point of not using the ready made module was that I wanted to add a volume control. Apparently scaling Vin is not how one supposed to do that. If I go up or down from the spot where the audio is good, I get distortions, but never a quieter signal.

I also tried to add a pot between pin 1 and the ceramic capacitor that goes to pin 8. The datasheet has three examples:

  • gain 20: by default there is a 1.35 kΩ resistor
  • gain 50: use a 1.2 kΩ resistor
  • gain 200: use no resistor

I only had a 2k potentiometer and when I dial it from 0 Ω up, the signal gets a bit quieter, but I can't get it down to silence. If I remove the circuit between pin 1 and 8 to operate at gain 20, the output is pretty quiet though.

I searched the Internet quite a bit, and I probably miss something obvious. It would be awesome to get some pointers.

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2 Answers 2

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You probably used a linear (B) taper pot. For audio you want an (A) log taper pot, so your 500 ohms will be about 25% of full electrical rotation, not 5%.

Image from this site.

enter image description here

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  • \$\begingroup\$ I meassured my pot an it is indeed lin, but that does not explain that it goes from noise to audio to noise. With a log one the range is easier to adjust, but I don't believe that the place where one should add the pot is where one can adjust the volume. It sounds like it should work, but then I should be able to control the volume a bit at least, right? \$\endgroup\$ Commented Jan 8, 2019 at 20:47
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  • Gain of 20 is too quiet
  • Gain of 200 is too distorted and can't turn it down to get quiet.

Choose Gain =50 with 1.2k in series with cap

Pots do not have a 60dB dynamic range so they usually gang 2 pots {pre-amp gain & power amp gain} to get 30dB in each.

Solution

Ganged Pot

schematic

But as Dave say's that needs to be an audio log pot.

enter image description here

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  • \$\begingroup\$ You could get 20log(500/10k)= - 26dB which is not silent that's the approx 30dB limit I said in my answer \$\endgroup\$ Commented Jan 8, 2019 at 21:18
  • \$\begingroup\$ Isn't this very impractical to adjust volume using 2 potentiometers? \$\endgroup\$ Commented Jan 8, 2019 at 21:31
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    \$\begingroup\$ They make stereo ganged pots which you can gang to 4 but like said in integrated receivers they gang preamp gain with power amp gain or something better like digital pots. (not for newbies) \$\endgroup\$ Commented Jan 8, 2019 at 22:07

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