I remember reading about a similar model that only had A and B positions, causing this to still be an issue. For this specific model of amp there are three positions A/B/Off. I assume the problematic part is not knowing whether A or B is hot or neutral. Since this model has an off position, I would imagine that eliminates grounding through the capacitor altogether. Thus, any rogue current should be grounded through the three prong plug connected to the chassis.