AT-1 VOLUME CONTROLLER
Introduction
TheAT-1 has been designed to be used in conjunction with the SENTRY MK2 environmental noise control unit. It is a
digitally controlled stereo unit and its purpose is to control the volume level of an audio system connected to it, without
cutting off the system completely. It will control the connected system to the maximum level allowed as defined by the
Sentry Mk2, thus removing the worry of having to continually watch levels. It does this without affecting the dynamic
range of the music being played, and because the control chain is microphone driven the amount of absorption which
takes place when a venue is full of people is automatically catered for.
More than one unit may be connected to the SENTRY MK2 to control more than one audio system. This is particularly
useful as it means that the house system and a visiting system, band, etc. can be controlled to the same maximum
level. The Sentry will automatically control theAT-1 that is in use.
It is in the interests of a visiting band or DJ to connect to theAT-1 where a Sentry is installed so that they do not suffer
the embarrassment of being cut off if they play too loud.
In the past control units monitored the signal level passing through a system to control the maximum level available.
This approach works fine but the system has to be calibrated to determine the relationship between the signal level and
the actual sound pressure level being produced. This makes it impractical to control visiting systems by this method.
This has now changed with the introduction of theAT-1. Because the control information is derived from a microphone
system (i.e. The Sentry) calibration is no longer required; therefore any system may be connected and controlled
bearing in mind a few common sense points. If the visiting system is not connected to theAT-1 the Sentry switching the
available mains power in the usual manner will control it. We feel that this will encourage visiting systems to connect to
theAT-1.
CONNECTIONS TO THE SENTRYMK2
THESE CONNECTIONS MUST BE AS LISTED BELOW
A 4 CORE CABLE IS REQUIRED - ALARM CABLE OR SIMILAR SHOULD BE USED. IF IT IS
SCREENED (WHICH IS RECOMMENDED FOR LONG RUNS) CONNECT THE SCREEN TO PIN
1 OR MIC SCREEN
AT-1 CONNECTOR SENTRYTERMINAL
PIN 1 REMOTE MIC SCREEN
PIN 2 SLAVE OUT +
PIN 3 WARNING LED
PIN 4 12 VOLT CONTACTOR +
SWITCHON
When first switched on theAT-1 will be at full attenuation. When the Sentry is reset the unit will fade to no attenuation.
This will take several seconds and is quite normal.
The Sentry timer should be set at about 20 seconds (mid point on timer pre-set), this is the factory setting. If the Sentry
is tripped for any reason (security loop broken, Mic tamper, etc) the AT-1 will go to full attenuation.
CALIBRATION.
N.B.DO NOT PRESS THE CALIBRATION BUTTON UNTILTHE DISPLAY IS SHOWINGACONSTANT 0dB
Calibration is recommended when using the unit for the first time with a particular Sentry To do this proceed as follows:-
with no inputs connected to theAT -1 generate a sustained noise that lights the Sentry display to the amber LED 0dB
point (a note on a keyboard or a tone generator is useful for this). Then press the CALbutton on the rear of theAT-1
using a small screwdriver or similar. This procedure will give the most accurate control and allows for any component
tolerance between Sentrys. If not carried out the unit will still work.
Users cannot cheat as the unit will accept only a small range of adjustment to compensate for component tolerance.
OPERATION
Connect theAT-1 between the mixer and power amps using the jacks or XLRs provided. The system volume will be
controlled if necessary as determined by the sound pressure level (SPL) which the Sentry Mk2 Is set at.
The fade times will vary depending on the amount that the SPL threshold has been exceeded.
