One source for DIY passive preamps is www.goldpt.com. Arne Roatcap has designed Elma switches with circuit boards, in various configurations, and has at least one schematic for a passive. He's a helpful source of advice too. If you want info from me on what I've built, email nicetom@sonic.net. I used Elma switches once, Shallco several times, from either The Parts Connection or directly from Shallco.