Over the years, quite a few theremin designs have been drawn. Their quality varies from toy or gadget devices via hobby theremins to carefully designed instruments. I've tried to put each circuit diagram in the appropriate category. A special category is that of the vintage theremins, like the RCA theremin. And then there are, some even modern, vacuum tube theremin designs. You can use these schematic diagrams to build your own theremin or for reference when you wish to design or modify one. However, if you're not experienced in electronics you are probably better off with a theremin kit. (Max Baars)