The Chetboard

the idea of shielding is making a Farraday cage which is to have all the walls of a room or in this case, a cavity, made of conductive material and grounding those walls.

Looking at the picture I wonder what would happen if one were to steel wool the upper edge of the cavity to bare metal to make sure there is good electical contact between the top edge of the cavity and (what I hope is) the foil of the underside of the lid.

I know it's a little late from looking at the dates posted, but I had a 1982 CEC I picked up used and found it had the same buzz, and I put a brass plate under the saddle, same size as the saddle, and ran a wire from that to ground of the controles and the battery compartment. And it helped in My case. because the way I got it You couldn't even use a in line tuner the buzz would peg the meter. So if someone else get's one of these older model's I would try that before getting rid of it. Because it sounded great recorded direct.

P.S. lightly sand the brass plate and the underside ( metal bottom of the saddle) for a good contact ground. It worked for Me.