Guitar Headphone Amp and Preamp K4102
You get everything needed to build what is shown, including the case. The assembly instructions and schematic are here. Designed around the NE5532 low-noise dual op-amp, runs off a 9-volt battery. Has a stereo headphone output and a line level output for driving recording gear, etc. Output level is set by a board-mounted trimpot; the knob is a tone control. I figure that most players will need to match a 1/4" plug to the RCA female input, so an adapter is included.