need an onboard preamp/ mixer

[lathamuse]

Hi, I am after all the help I can get, I am in the process of building an archtop and want till mix/blend 2 coil splitting humbuckers (passive), with either an endpin preamp electret mic, or passive transducer, I'm wanting to fit under scratchplate, size matters, 17 mm deep,45 x75 mm for board are my limits, I will put shaft through scratchplate, I'm a fulltime musician so cost matters! Can somebody please help me, I would really appreciate any help, pointers advice, thank you, Paul