Input green: Positive/Hot
Input orange: Negative/Cold
OP amp suggested: 4580
Frequency response: 15Hz-80kHz
Powered by a single 9v battery.
The 1k resistors for the voltage divider on each non-inverting input should be ideally perfect so 1% tolerance resistors are suggested. Also you can multiply by 10 the values of the resistors for the voltage divider and the gain setting of the op amp to reduce the power consumption but keep in mind that doing that will increase the noise on the circuit.
The pot should be logarithmic. If not, you will hear the volume not changing until the end of the travel.
How it works:
The first op amp works in differential mode, this is because if there is some noise in the signals it will be the same. If the signal of each input it's the same, then the output will be 0. The first op amp has a gain close to 1. In the non-inverting input an offset of 4.5v is added so the output signal can swing the full range.
This is my try to replicate something like the Behringer P2.
