Voltage drop in a Permanent Magnet Generator
Since this turns out to be an anemometer - oh, the torture we go through to extract relevant details from the questioners! - and it's probably related to your Schmitt trigger question I suggest you try a different approach. I presume you will feed this into a micro-controller to calculate the wind speed. 

If so, you could use an op-amp based precision rectifier to convert the signal to DC and use a potential divider to feed it to the micro ADC. The PMG p-p voltage should have a linear relationship with speed.