MUTE FEATURE ADDITION FOR THE BIG BRIAR ETHERWAVE® THEREMIN

DESCRIPTION: This circuit provides a useful addition to the popular Etherwave® Theremin for occasions when the player desires to silence the instrument while in the vicinity of the antennae. Although this may be accomplished by simply turning the instrument off, an undesirable "pop" will occur in the process. In addition, the instrument's settings may drift slightly when it is turned back on and "warms up."

The scheme employed in this circuit will provide a "popless" muting function. In addition, the MUTE STATUS light-emitting diode doubles as a convenient "power on" indicator.

In the trial application, this circuit was constructed using Wirewrap (TM) terminals and a 14-pin Wirewrap (TM) IC socket on a 2" x 1.5" perforated board. The board was mounted on a spacer, and attached to one of the instrument's existing circuit mounting posts, located behind the two right-hand front panel controls. The MUTE CONTROL switch and MUTE STATUS light-emitting diode were connected to the board via thin, 26-gauge wires that were routed outside the instrument's enclosure through a space to the right of the control panel. The switch and LED were mounted on a small plate, and left unattached from the Etherwave's cabinet. This type of construction was used to preserve the instrument's appearance, however, the user may optionally mount the switch and LED on the instrument.

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 upon each momentary actuation of switch S1. Resistor R2 is a current limiter that protects U1 from static electric transients which may couple through the switch. Transistor Q1 translates the levels into -16 volts and 0 volts, respectively, 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 shunts the volume control voltage when its gate is at 0 volts, muting the output, and allows the control voltage to be present when its gate is at -16 volts. The inclusion of R6 and C3 permit a controlled rate of transition between the two modes, thus preventing "pops" in the audio output. The remaining logic inverters are used as a driver for the two-color LED.

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, TRANTALUM	1 uF	PANASONIC	ECS-F1VE105K	DIGI-KEY	P2059-ND	1
C2,3	CAPACITOR,CERAMIC	1 uF	PANASONIC	ECU-S1J105MEB	DIGI-KEY	P4920-ND	2
LED1	LIGHT-EMITTING DIODE	RED/GREEN	LITE-ON	LTL-293SJW	DIGI-KEY	160-1038-ND	1
Q1	TRANSISTOR	PNP BIPOLAR	NATIONAL SEMICONDUCTOR	2N3906	DIGI-KEY	2N3906-ND	1
Q2	TRANSISTOR	N-CHANNEL JFET	CENTRAL	2N5484	MOUSER	610-2N5484	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	HARRIS	CD4069UBE	MOUSER	570-CD4069UBE	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

Text and images ©1998 by Arthur Harrison

Back to the Opening Page of Art's Theremin Page