I'm trying control the volume of a small speaker (8Ω, 1/4W) in a 3.3V system using a potentiometer wheel (10kΩ). I've done this in the past using an LM386 in 5V systems, but the project I'm working on is 3.3V only. I've been browsing Digi-Key for a 3.3V equivalent, but of the ones I've looked at so far (LM4864, LM4862, TPA301, TS34119), I can't seem to understand how to control the volume in their typical application diagrams (with a pot or otherwise).

Does anyone have experience with something like this?

  • \$\begingroup\$ AT 3.3v you may want a modern class D amp intended for mobile devices, and you'll want one that can drive both sides of the speaker. \$\endgroup\$ – Chris Stratton Jun 29 '18 at 4:46
  • \$\begingroup\$ What do you mean by both sides of the speaker, like left and right channels? \$\endgroup\$ – MyFingerHertz Jun 29 '18 at 11:31
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    \$\begingroup\$ I think he means a BTL (bridge tied load) driver. It drives one side of the speaker with a signal, and the other side with an inverted copy of the signal. Eliminates coupling caps and provides 6dB higher output from the same supply voltage. \$\endgroup\$ – Cristobol Polychronopolis Jun 29 '18 at 11:54

for TPA301 \$R_F\$ is the volume control

see datasheet page 16 figure 26

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  • \$\begingroup\$ Page 10 seems like it just has graphs of the gain vs frequency... but I see your point about Rf being for gain control in the component selection sectiob. So I think I can replace it with a variable resistor? Because their examples all only show a 50k static resistor \$\endgroup\$ – MyFingerHertz Jun 29 '18 at 11:35
  • \$\begingroup\$ He might have meant page 16. I'd use a 50K pot with a 5.6K fixed resistor on each side, and the center tap going to pin 4 of the TPA301. This will satisfy the impedance limitations on page 16. One 5K connects to the input cap and the other goes to pin 5. \$\endgroup\$ – Cristobol Polychronopolis Jun 29 '18 at 12:03
  • \$\begingroup\$ Do you think a 10k pot would work if I used 1k fixed instead? Just so I have to source a few less parts ;) \$\endgroup\$ – MyFingerHertz Jun 29 '18 at 13:15
  • \$\begingroup\$ yes I meant page 16 (edit made), 10K might not work as well as the 50K, \$\endgroup\$ – Jasen Jun 30 '18 at 7:59

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