Marakanetz, I suspect that your vta is set to high and when you apply more tracking force this will lower your vta. You should set your tracking force to the recommended weight, and adjust your vta until all the instruments are heard clearly,or come into focus. If your arm does not have adjustable vta then I think you know why you have to track heavy to get better sound. You will not get the magic unless you have both the tracking force and vta right.
