SoundCraft SM12 User Manual page 31

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The master module contains the stereo mix or sidefill output, the operator's
headphones and wedge speaker outputs, a noise or sine wave test oscillator, the solo
mode controls and master solo clear function, and internal/external talkback
functions.
PSU Status Indicators
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The two PSU Status Indicator LEDs (red) show that the +/-17V and +48V PSU
rails are working.
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Talkback
The talkback system allows communication by the operator to the group and mix
outputs, and to and from the front of house (FOH) console.
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The TALKBACK MIC XLR accepts a local talkback microphone or
gooseneck.
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3
The TALKBACK LEVEL control adjusts the sensitivity of the talkback mic
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input. The sensitivity of the mic input is variable between -20dBu and -50dBu.
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4
The TALKBACK TO BUSSES EXT button sends the T/BACK IN signal to
the group and mix buses when FOH talkback is active to allow the front-of-house
engineer to talk to the performers via the monitor outputs.
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The TALKBACK/OSC TO BUSSES INT button routes the talkback signal
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from the mic to all group busses and the stereo mix bus simultaneously. The
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oscillator is also routed via this switch if it is turned 'on'.
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The momentary action FOH button initiates talkback to the front of house
25 console using a Soundcraft proprietary system. The talkback mic signal is switched
to the FOH OUT XLR, with a +15v DC common-mode voltage to signal the FOH
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console that talkback is occurring. The signal present on the FOH IN XLR is fed to
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the 'phones, dimming the existing signal by 15dB. The wedge is dimmed by 20dB.
An internal jumper disables the common-mode DC voltage, to allow use with
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non-Soundcraft desks.
If a 15v common-mode voltage is detected on the FOH IN XLR, indicating talkback
from the front-of-house console, then the FOH IN signal is switched to the 'phones
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output, dimming the existing signal by 15dB, and dimming wedge output by 20dB.
The FOH switch also lights.
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The signal from the talkback mic. may be routed to the group or mix outputs
individually by pressing the TB button on each output; this also dims the wedge
output by 20dB.
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Master Module