Schematics for compact cassette deck's

I want to update a cassette deck output from the standard garbage innards to something a bit more high quality. I would like to build a very good preamp circuit to transfer some irreplaceable cassette recordings to 24/96KHz digital via an analog balanced input computer sound card. The thing is, I can't find any schematics anywhere on the net. Does anyone know of a site that has high-end schematics to build one?