Harmonic distortion, odd and even order
Discusses how different devices, vacuum tubes, bipolar transistors, etc., distort the inputs. It's a nice, simple, mathematical treatment.
A tutorial on exponential converters and temperature compensation
A simple tutorial on synthesizer exponential converters and how their temperature compensation works.
Thermal compensation of analog exponential converters
A survey of thermal compensation for analog synthesizer exponential converters.
Shmøergh Moduleur
An open-source, modular analog synthesizer system.
Yusynth DIY modular synth
A bunch of DIY synthesizer modules, including schematics and photographs.