10 MΩ piezo buffer pedal powered by DC adapter

Hi everyone, this is my very first thread.
My father and I are building a DIY piezo system to amplify my upright bass.
We've already made the pickup, now we need a buffer preamp because obviously if I plug the pickup straight to the input of my amp it sounds like absolute dog ****.
I've already tried googlin' some schematics, but I couldn't find any true solutions. I'd like to make it in a pedal format to include it in my pedal board for gigs and I'd also like it to be powered by a DC adapter rather than a 9V battery like all the designs I've found online. It'd be nice to have a HPF pot as well.
Thanks in advance for your help.