I've been talking to some of the
guys over on allaboutcircuits.com. They helped me improve the Shure circuit, like this:
Noticeably quieter. Imperceptibly quiet. The first two caps eliminate AC ripple current, while the .33mfd is a HPF I think to further eliminate any 50-60hz buzz. I tested it using an old OneSpot, but my Cioks should be even better.
I'm going to work on sticking this inside a box.
