MUTE FEATURE ADDITION FOR THE BIG BRIAR ETHERWAVE® THEREMIN
(A newer version of this circuit is here.)

DESCRIPTION: This circuit permits the addition of a "mute" switch to the Etherwave® Theremin, useful for placing the theremin in a silent mode without having to turn it off completely. There is no "pop" during the mute-unmute transition. A MUTE STATUS light-emitting diode doubles as a convenient power indicator.

The circuit was constructed on a small circuit board installed inside the theremin. The MUTE CONTROL switch and MUTE STATUS light-emitting diode were mounted on the front panel, near the output jack.

CIRCUIT DESCRIPTION: U1 is a six-section logic inverter. Sections A and B and associated components form a bistable circuit which alternately provides a 0 volt or -12 volt level with each momentary actuation of switch S1. U1B-4's output drives a LED control circuit comprised of U1C through F. LED1 illuminates red when the theremin is muted, and green when it is unmuted. R5 is the LED current-limiting resistor. R2 protects U1A's input from static transients.

U1B-4's output also drives transistor Q1, that translates the levels into -16 volts and 0 volts, controlling the gate of N-channel junction field-effect transistor Q2 via the R6-C3 integrator.

Q2's drain-source circuit is connected in parallel with the instrument's voltage-controlled amplifier control input. Q2 pulls the control input of the theremin's VCA  (U3) to -12V for full muting and opens for unmuted operation. R6 and C3 provides a controlled rate of transition between the two modes to prevent "pops" in the audio output.

Note:  Only major items are indicated in the Table. Items such as wire, terminals, circuit board, and fasteners are not shown.

April 6, 1998

Text and images ©1998 by Arthur Harrison

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