For the first year my Bernina acted up horribly. Finally I bought Gutermann cone thread for top threading and now my machines purrs. I only wind my own thread. I'm too afraid to try pre-wound bobbins. My machine is very picky when in comes to thread. When I have the right thread in it, it makes all the difference in the world. And I can't use spools, I have to use cones for some reason. But I'm just happy I finally figured it out and it's working great!