CIRCUIT DIAGRAMS
This is the basic circuit. It runs from a split supply of +/-12 to +/-15 volts. It will function at lower voltages but you will have to reduce the input level to prevent distortion from clipping.
An input signal around 500mV should be about the safe limit to give some room for the uneven recording level of many mp3s.
The op-amp used in the simulation was a general purpose 741 type but better quality performance may be gained by choosing a higher quality op-amp specifically for audio applications.
Below is a version for a single supply which should be a minimum of 12volts and preferably 18 to 24v for high input signals. In this case a V/2 reference is created by the potential divider R6,7 and decoupling capacitors added at the input and output.
