The Theremin has captivated engineers, music lovers, and musicians since the 1920s. Back in 2017, Elektor published an article and circuit to help readers build a Theremin featuring JFETs instead of vacuum tubes. Let's take a closer look.

Tube-Free Theremin

The complete JFET-based theremin circuit includes a second oscillator, a mixer, and a circuit for the volume antenna. The second oscillator is stabilized at 470 kHz by a ceramic resonator, and so it must be possible to set the adjustable oscillator to this frequency. A trimmer capacitor is provided for tuning.
 
JFET-based Theremin circuit
The complete JFET-based Theremin

"The circuit can be constructed on the copper side of an uncoated printed circuit board," Burkhard Kainka explained in his article. "This has the advantage of providing a good ground connection and decoupling the individual stages. Wherever a ground is needed, the shortest possible path can be used. This construction method, used along with small pieces of prototyping board (see Figure 10), can also be employed for more complex and higher-frequency RF projects. An interesting lesson from this project is that JFET-based oscillators are very stable in frequency, and insensitive to variations in supply voltage."
 
theremin in enclosure
The instrument in its enclosure

The circuit was constructed on the copper side of an uncoated PCB. This has the advantage of providing a good ground connection and decoupling the individual stages. Wherever a ground is needed, the shortest possible path can be used. This construction method, implemented along with small pieces of prototyping board, can also be employed for more complex and higher-frequency RF projects.
 
theremin main
 

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The article, “Build Your Own Theremin Using JFETs Instead of Vacuum Tubes,” appeared in Elektor March/April 2017, which is available to all Elektor Members. Our members enjoy ElektorMag, a 10% Elektor Store discount on many products, and full access to the online library. If you don’t yet have an Elektor membership, register now to start reading through our thousands of projects and circuits. Want to read more about Theremins? Check out “A Tube-Theremin” and “Analog Theremin.”

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