iPod to Car Stereo Low Volume

From Bath UK, 1 post

I have an iPod Mini and I am playing it through the aux jack on my Saab Stereo. However, the power output is very low on the iPod which means to get a decent volume on the stereo I have to crank the volume right up causing distortion and background hiss.

Does anyone know if there is a pre-amplifier available that has minijack input and output and can be fed by 12v?