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.





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

CAPACITOR,CERAMIC

1 uF

KEMET

C330C105K5R5TA

DIGI-KEY

399-4389-ND

1

LED1

LIGHT-EMITTING DIODE

RED/GREEN

LITE-ON

LTL-293SJW

DIGI-KEY

160-1038-ND

1

R1

RESISTOR

10K OHM, ±5%, 1/4 WATT

YAGEO

CFR-25JB-10K

DIGI-KEY

10KQBK-ND

1

R2, 5

RESISTOR

1K OHM, ±5%, 1/4 WATT

YAGEO

CFR-25JB-1K0

DIGI-KEY

1.0KQBK-ND

2

R3

RESISTOR

100K OHM, ±5%, 1/4 WATT

YAGEO

CFR-25JB-100K

DIGI-KEY

100KQBK-ND

1

R4

RESISTOR

2700 OHM, ±5%, 1/4 WATT

YAGEO

CFR-25JB-220K

DIGI-KEY

2.7KQBK-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

U2

OPTICAL COUPLER

FORM "A" PhotoMOS® RELAY

PANASONIC

AQY210EH

DIGI-KEY

255-1430-5-ND

1

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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