The Pasco 9307 Fourier Synthesizer is connected to a speaker and an oscilloscope. The synthesizer can generate two fundamentals of 440 Hz and eight higher harmonics, each with amplitude and phase control. The synthesizer can produce either sine, square or triangular wave forms. Note: While it works fine, there are several nice java applets available.
1) Pasco 9307A Fourier Synthesizer Instruction Manual and Experiment Guide.
2) An older manual is available for the 9307 Fourier Synthesizer. Note: This manual also includes two pages of schematics ( Page 1, Page 2 ), and a page of component locations.
3) Fourier Series Applet from falstad.com (Paul Falstad).