for pmillet sound card interface

Tonight I found out it is a really good idea to ground the shaft/body of the rotary switch in order to eliminate pick up of 60Hz and its harmonics. I noticed moving my hand closer to the metal knob on this switch resulted in a >20dB increase in 60Hz spectra and the addition of somewhat lower level harmonics at 120Hz, 180Hz, and 240Hz.. I grounded the switch with a piece of 28ga wire between the lock washer and the body of the switch and grounded it to the board ground. This totally eliminated any pick up with no noticeable line frequency or related spectra. (My case is totally shielded on the top and bottom, but not sides, front or rear - and does not appear necessary to do so.)