Much thanks to everyone!
great solution from tafffy. you can also passively control a piezo rod with a capacitor across the input. different value different tone.
Hi, thanks for your comments guys.
Tip: if you build a number of different cbg's for your own use, to save some expense what I did some years ago was to build the pre-amp you see in photo into small box, a la stomp box, and use it for many guitars.
Also if you are demoing to a potential customer play though it, it makes things sound a lot better, and shows the potential of a CBG.