I'm replacing an old MEC preamp in my 1990's Warwick with an Aguilar OBP-2sk. The old volume pot with active/passive swich is shot. I want to wire the new Aguilar preamp with the passive option utilizing a push/pull volume pot. Do I need a 250k or 500k pot? The pickups are older passive Seymour Duncan jazz single coils. Also, what's my best option for a new blend pot? The current pot works fine, but I might as well change them all out while I'm at it. Thanks!