I''ve got a Dean Pace vertical-fretless-electric-bass-on-a-stick (I'll call it that since a lot of folks seem to get their panties in a bunch if I dare call it an electric upright

) and have what seems to be the universal problem with the Dean Pace model - i.e. buzzing/humming caused by the bad earthing.
I've been going nuts trying to get a permanent fix for this as every time I take the bridge off and re-seat the earth wire, the problem goes away for anything from a few weeks to a couple of months but always returns eventually.
I had a flash just a few minutes ago; since the noise is coming from the pre-amp, I'll bypass the pre-amp and just connect the bridge directly to the output jack and use one of my stand-alone pre-amps (probably one of my SansAmp BDDI's) to match impedance with my amps input.
If I do this, given that the impedance of the bridge piezo is on the megohm range (I assume), is it possible to have a passive volume pot on the Bass? If so what value? It's no big deal if I run the bass without a volume control, as I normally just run the Bass flat-out and use the amp's volume control but it's always nice to have one on the instrumenr "just in case".