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(A newer version of this circuit is here.)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: 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.




REVISIONS

DATE

REV. NR

DESCRIPTION

6 April 1998

Release

-

7 April 1998

001

Change Q2 from 2N3819 to 2N5484 with VGS(off) specification of -3 volts to ensure operation under low unregulated negative supply conditions.



PARTS TABLE

ITEM

DESCRIPTION

VALUE

MANUFACTURER

MANUFACTURER PART NUMBER

SUPPLIER

SUPPLIER CATALOG NUMBER

QTY
C1 CAPACITOR, TANTALUM 1 uF KEMET T350A105K035AS DIGI-KEY 399-1429-ND 1
C2,3 CAPACITOR,CERAMIC 1 uF KEMET C330C105K5R5TA DIGI-KEY 399-4389-ND 2
LED1 LIGHT-EMITTING DIODE RED/GREEN LITE-ON LTL-293SJW DIGI-KEY 160-1038-ND 1
Q1 TRANSISTOR PNP BIPOLAR FAIRCHILD SEMICONDUCTOR 2N3906 DIGI-KEY 2N3906FS-ND 1
Q2 TRANSISTOR N-CHANNEL JFET FAIRCHILD SEMICONDUCTOR 2N5484 HARRISON
INSTRUMENTS		 07933-5961-2N5484 1
R1, 5 RESISTOR 10K OHM, ±5%, 1/4 WATT YAGEO CFR-25JB-10K DIGI-KEY 10KQBK-ND 2
R2, 7 RESISTOR 1K OHM, ±5%, 1/4 WATT YAGEO CFR-25JB-1K0 DIGI-KEY 1.0KQBK-ND 2
R3, 4 RESISTOR 100K OHM, ±5%, 1/4 WATT YAGEO CFR-25JB-100K DIGI-KEY 100KQBK-ND 2
R6 RESISTOR 220K OHM, ±5%, 1/4 WATT YAGEO CFR-25JB-220K DIGI-KEY 220KQBK-ND 1
S1 SWITCH SPDT MOMENTARY C & K 8125SHZBE DIGI-KEY CKN4022-ND 1
U1 INTEGRATED CIRCUIT CMOS HEX INVERTER TEXAS INSTRUMENTS CD4069UBE DIGI-KEY 296-3518-5-ND 1

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



April 6, 1998
Parts Table updated September 14, 2018

Text and images ©1998, 2018 by Arthur Harrison

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