I did some tests and whatever I run the thunder at I add 1 to 1.5 volts on the fehu. For me 9 v is good for lining on the thunder but 10 to 10.5 on the fehu gets me the exact same lining goodness worked great for dropping in some bold lines with a 9 round shader for me today effortlessly and first pass . . I like the fehu so much I just picked up their direct drive for fun just waiting patiently for it to arrive now I got the 4.0 fehu it's a fantastic machine I like the easy access by removing the faceplate etc for cleaning and the 4.0 is producing great smooth shading for me