Mag/piezo phasing / new pickup recommendations
 

Hi folks,

I recently changed out the previous bridge and undersaddle transducer on my fretless Stambaugh with a Graphtech-equipped Hipshot bridge. I used Graphtech's Acoustiphonic preamp to mate the bridge to my Bartolini P25CBC dual coil humbucker. All wiring was checked by my local luthier.

Here's the issue I'm having:

The Acoustiphonic preamp features a mid/dark switch and when I have it set to 'mid,' and I dial in my magnetic pickup, the sound gets thin and uneven.
the folks at Graphtech, who have been super helpful as I've worked out a few user error issues, suggested it could be a phasing issue, so I reversed the leads from the pickup. That corrected the phase issue, but now I have a ground hum from the mag pickup whenever I'm not touching the strings.

I have a Carvin humbucker that works just fine, but it's one of the new radiused models and I don't think the curvature is a proper match for my fingerboard, so it's not an ideal solution.

Any suggestions, advice, replacement mag recommendations, etc.?

- thanks