I'm going to install an active 2 band preamp in a Jazz bass. However, the preamp that I have has separate bass and treble. I'd like to install a stacked bass and treble to conserve space and keep the input jack on the control plate. I'm looking online at various part suppliers (www.stewmac.com, www.basspartsresource, www.warmoth.com) and they have 250k, 500k and 250/500k dual concentric pots. Is there a correct one to use or does it not matter? What is the difference? The present pots that are on the preamp, I believe, say B30K. The preamp that I have is pretty much a no name preamp that I scored off ebay for dirt cheap but it sounded pretty good in another bass that I had. It looks similar to a bartolini HR-4.5. Any help or advice? Thanks!!!!