I want to build a quality Guitar/Bass preamp.

There are zillions of schematics on the 'net for how to build your own mic preamp and plenty of articles on the pros and cons of each style/topology etc. but there is almost nothing on building a hi impedence preamp for guitar/bass. Whats the best approach? High quality transformer on the input? Op-amps? boutique hand-crafted transistors? less-is-more? My aim is as quiet and transparent as possible.

I may indeed be barking up the wrong tree. If a well-grounded, well-shielded guitar in a room with as little as practical EM interference will still generate more noise than your average preamp, then my question becomes irrelevant. I'm quite aware that shielding and grounding and elimenating EM noise sources are the primary step, but those things have to be done on a guitar-by-guitar, location-by-location basis. Building 1 good preamp is something I could do once and never have to second guess again. I'm not looking for something that is going to add "air", "richness" and "magic" to the signal and I realise that (similar to reference monitors) accuracy is often not flattering. I just want to get the signal from guitar to the computer with as much of the frequency response as I need (which isn't huge, as you've said) with as little noise/distortion/everthingelse as I can. If thats really a trivial task, then so be it.

nerd. you can actually build a direct box useing a cheapo 2n3819 fet. and no expensive transformer. i tried some esoteric fets once n didnt notice any diff from a cheapo fet available at the shack like the 3819. or my 30 buk art tube mp. ive also tried fancy op amps. the advantage of fet's (and high imp op amps) is they offer the high impedence that geetars n basses like to look into. if your really into the diy madness then try test recorded traks with a esoteric circuit or diy and then a cheap mp. mebe youll notice a massive diff..but i didnt.