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I want to connect phone output to a car radio. It has + and - inputs. When I connect left channel to the + input, there is good quality sound, but it's not as loud as CD player. If I invert right channel, then plug it in the - input, the sound should be 6 dB louder. I know that this can be done with an inverting amplifier, but is there a way to do this programmatically on android?

Btw is 1,5 degree phase change too much for bass? I simulated this circuit and these are the results. Inverting amplifier AC sweep results If I change R4 and R5 to 50 kΩ, phase and magnitude changes will decrease. On the other side, transient start up time and noise will increase, but besides that, will anything else be affected, like input bias current correction?

EDIT: This is Sound System manual(page 38).

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    \$\begingroup\$ I think your question is fundamentally flawed. Unless it's ancient, the radio should have a stereo input and you would just run a stereo signal into it. + and - inputs sounds like a differential input and that would be very unusual. Make, model, link to user manual? \$\endgroup\$ – Transistor Jul 15 '19 at 12:28
  • \$\begingroup\$ I'm voting to close this question as off-topic because it is asking how to control audio volume with Android software. \$\endgroup\$ – Elliot Alderson Jul 15 '19 at 12:28
  • \$\begingroup\$ @LEM: You forgot to specify which inputs you're using. I'd be using C18, 19 and 20. \$\endgroup\$ – Transistor Jul 15 '19 at 13:04
  • \$\begingroup\$ @Transistor I used Phone Inputs C7 and C12 for signal and ground. I thought that C8 is for balanced signals. \$\endgroup\$ – LEM Jul 15 '19 at 13:24
  • \$\begingroup\$ That might work but you'll only have a mono signal. Surely you want stereo? \$\endgroup\$ – Transistor Jul 15 '19 at 13:27
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Regarding the electrical interface you need stereo sound so try to use the CD inputs.

  • C18: GND.
  • C19: Left.
  • C20: Right.

Get a cheap pair of headphones or a 3.5 mm stereo jack extension lead and cut the headphones off. Connect the tip to C19, ring to C20 and sleeve to C18. (Use your multimeter continuity tester to identify the cores.) Try it out and if it works then do a decent permanent job. You may be able to find a push-on spade receptacle at a motor parts supplier.

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