AUTOSWITCH
HENRY ENGINEERING
503 Key Vista Drive
Sierra Madre, CA 91024
Tel: 626.355.3656
Fax: 626.355.0077
www.henryeng.com
TM
STEREO AUDIO SWITCHER + SILENCE SENSOR
DESCRIPTION
AutoSwitch is a versatile stereo audio switcher and silence sensor. It can be used to manually or automatically
select between two stereo audio sources. Manual source selection is controlled with a GPI contact closure or DC
voltage; automatic selection is via the silence sensor. When automatic operation is used, the silence sensor
monitors the “A Input” audio levels. If the level of either (or both) channels drops below the silence threshold for the
delay time preset, the unit switches to the “B Input”. When the A source audio returns, the unit resets and switches
back to the A input. The silence threshold and time delay are adjustable for each channel. An Alarm relay output is
provided to activate an external alarm or other equipment. Gain trims are provided for each audio input.
INSTALLATION
Audio and control circuits for AutoSwitch are via plug-in euroblock connectors. Remove about 1/8” of insulation,
insert the wires into the plugs, and tighten the screws. Be certain that no bare wires are exposed. Audio inputs
may be either balanced or unbalanced; for unbalanced sources, jumper the – input to GND. For unbalanced
outputs, connect to the + and GND terminals only. Do NOT short the – output to GND.
If manual control will be used to switch between A and B inputs, connect to the CONTROL connector as follows:
For GPI control (contact closure or open collector), connect to – and GND. (Open collector to –, Ground to GND.)
For control via a DC voltage, first open the unit and disconnect one end of R45, a 1K resistor. Connect the DC
control signal to the + and – control inputs. BE SURE to include a current limiting resistor in series with one input
lead! (For 5vdc to 12vdc, use 1K; for 24vdc, use 2K.)
AutoSwitch has an ALARM relay that activates when the silence sensor trips. Its terminals are on the CONTROL
connector. The NO and C terminals close when the silence sensor trips.
CALIBRATION AND SETUP
Once AutoSwitch has been installed, the audio levels and silence sensor adjustments should be calibrated.
Each audio input has a pair of level adjustments; adjust to produce the desired output level. (Unity gain is achieved
when the trimpots are set to mid-rotation.) Note that the unit will default to the A source, unless manually switched
to B, or unless the A audio level is below the silence sensor threshold. The GREEN LED indicates the active input.
To calibrate the silence sensor, set the SIL SEN and ALARM switches to ON.
The A source is always monitored by the silence sensor. There are separate level (LEV) and delay time (DEL)
adjustments for each (L&R) channel. The YELLOW LEDs will light whenever audio falls BELOW the silence
threshold. Turning the LEV trimmer clockwise INCREASES the threshold, making the silence sensor more apt to
trip. Turning the LEV trimmer counter-clockwise REDUCES the threshold, making the sensor less apt to trip.
Watch the yellow LEDs and adjust the LEV trimmers so the LEDs light when audio falls below the desired level.
The DELAY time trimmers determine the time the A-source audio must stay below the threshold before the silence
sensor trips. Turning the trimmer clockwise increases the delay time. The normal range is from 3 sec. to 20 sec.
(This range can be increased by removing R47 and R56. In this mode, the delay range will be from about 20 sec. to
35 sec.) NOTE: The shorter of the two delay settings always takes precedence: the unit will trip when the shorter
of the two delays “times out”. In most cases, the two delay trimmers should be set to about the same delay time.
The RED LED will indicate when the silence sensor has tripped. The GEEEN LED will confirm when the B audio
source is active.
(2 pages)
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