Here is a circuit that boosts audio levels to 0-4v.
http://macetech.com/vuinput01big.png
What I do not understand is why the battery is connected to the non-inverting input of the op-amp. I breifly tried this setup with my mp3 player and I nearly fried it
http://macetech.com/vuinput01big.png
What I do not understand is why the battery is connected to the non-inverting input of the op-amp. I breifly tried this setup with my mp3 player and I nearly fried it