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Electronics Projects For Musicians by Craig Anderton (1980, published by Amsco Publications) contains detailed instructions to build your own ring modulator. The project is relatively easy to build for the experienced solderer. The design uses two IC's and runs off two 9 volt batteries. You supply the input (your amplified quarter-tone trumpet or any instrument pick-up or guitar, keyboard, microphone, etc.) and the output (a mixer input or power amplifier.)
Note: the design in the 1980 edition of the book is better than the 1978 version.
To make things even easier, PAIA Electronics sells kits for all of the projects in Anderton's book. They sell the printed circuit board for the ring modulator by itself, for $8.95 and the full ring modulator kit with all the parts you'll need (except for an enclosure) for $29.95.
PAIA Electronics 3200 Teakwood Lane Edmond, Oklahoma USA 73013 (405) 340-6300 (405) 340-6378This ring modulator is probably pretty similar in performance to the one that Don Ellis used. There are more modern options also. The Alesis Quadraverb Plus contains a ring modulator which is much more high tech that anything Ellis ever had available. It is computer controlled and the pitch stable. On the Quadraverb you can change the carrier frequency with a MIDI signal. Remember that Ellis died right before the MIDI revolution. It is scary to imagine what he might have done, had he lived a few more years.