MUTE FEATURE ADDITION FOR THE BIG BRIAR ETHERWAVE® THEREMIN, VERSION 2

DESCRIPTION: This is a new version of the Etherwave® Theremin mute circuit. Like the original version, it provides a "popless" muting function and has a two-color light-emitting diode to indicate when the instrument is muted (red) or unmuted (green).

This version was installed in a unit that was provided with an external DC power supply to reduce mains hum in the output. (With the external DC power supply, the -18 volts required for the original version of this circuit is not available, so this version was designed to require just -12 and +12 volts.) This version may be used in either stock units, or ones modified to accept external DC power.

The prototype of this 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 at U1B-4. Each  momentary actuation of switch S1 alternates the states. 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 controls the input of PhotoMOS® optical coupler U2. U2's output acts as a switch that pulls the control input of the theremin's VCA (U3) to -12V for full muting and opens for unmuted operation.

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

August 29, 2009

Text and images ©2009 by Arthur Harrison

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