Synth DIY books
Electronic Music Circuits, Barry Klein
Electronic Music Circuits by Barry Klein
Electronotes, ed. Bernie Hutchins
Electronotes - Classic synth design.
Musical Applications of Microprocessors, Hal Chamberlin
Hayden, 1985 ISBN 0810457687, 802 pages (2nd edn)
Although primarily concerned with microprocessors and their use within sound and music synthesis, early chapters have introductory material on synthesis in general, including methods using tape, voltage control etc. There is also a nice chapter giving typical examples of basic analogue circuits such as VCOs, VCFs, VCAs etc., with good explanations of how they work.
Op-Amp Cookbook, Walter G. Jung
<add desc> 1st edition good too..
Small Signal Audio Design, Douglas Self