The switch cavity with copper shielding. Step-1) - I simply cut a rectangular piece of foil a little larger that the bottom of the cavity. I stuck it in place with some of the foil coming up on the sides. A few relief cuts with scissors allowed the foil to fit nicely. Remember to open the holes for the wires and input jack. You can see the hole in the foil for the input jack - top right of the control cavity.