Anniesue, it may be a similar thing as Pfaff QE4.0. The bobbin holder part(which is builtin) has a little raised area in the center where the bobbin sets and that has some kind of a sensor. I suppose it senses when the bobbin is empty. So that might not work if you used a pre-wound. But I don't know if it would harm anything. Maybe someone who has a Bernina or QE 4.0 can answer better.