My 15 year old musician son has developed a keen interest in the circuitry behind analog and digital synthetizers, and wants to build his first component for a custom synth, a VCO board. We have the PCB, I'm gathering the components, and have given him an intro to electricity and electronics, what the components are and what they do, but I need a good book that, at a junior high school level, explains all the concepts, and does so within the context of a fun read (dry conceptual material won't get to first base with a 15 year old).
Suggestions?