So I copper clad proto-ed the grayhill rotary switch into my PD thing. I can post pics.. at 1 MHz an inch of bus wire is not a big deal. Anyway with the switch body grounded the step response/ BW went to crap. (100 k ohm FB) When I floated the switch with my dremel, and I got a nice improvement in BW ~400 kHz to 800 kHz (I wasn't looking at the step response at the time.. and BW measurements are squishier than the time domain.)
Anyway then I tried driving the switch body from the input signal, I got a little improvement. (In step response.) My thinking was that the driving the switch body, would pull all the un-connceted switch pins along with it. And now I'm thinking if I drive it a bit over unity...? or is that the road to misery?
I could add a shell connected copper plane under the switch and add a circular copper fence.
George H.