On Tue, 8 Nov 2011 21:07:44 -0800, DaveC wrote:

Latest rev:

http://i40.tinypic.com/35m026h.jpg

What needs to be reference to the new "ground"? Everything between the
input
caps and output caps?

Pretty much... each of the op amps' noninverting inputs, and the
"bottom ends" of the potentiometers, as you have drawn them. *NOT*
the V- input to the op amp(s), of course.

You do mean each of the op amps' *inverting* inputs, yes?

---
No.

Your drawing is wrong; signal goes to the inverting (-) inputs and the
Vcc/2 reference goes to the non-inverting (+) inputs.

--
JF