I am working on an audio amplifier PCB circuit, where I have used LM386 as an amplifier, an aux jack for audio output, and a small speaker of headphones (30 ohm). I have two 220 uF molded and one 470 uF Alu. electrolytic capacitors parallel to the speaker and aux. You can understand from the figure.
I am facing some problems with audio amplification when the Aux is attached to the external MP3 player or Bluetooth MP3 player. Audio is not amplified specially low frequencies.