6
Field Wiring
,
Continued
Ground Fault Detection of Audio Riser
The output of the riser driver transformer is referenced to DC common of the power supply that is
used to power the amplifier system. Because the riser is referenced to DC common, ground fault
detection of the audio riser is possible.
Only one power supply used in the system with same DC common should have ground fault
monitoring enabled. If the other power supplies are used in a system with the same DC common
wired together, their ground fault circuits should be disabled for proper ground fault detection.
Audio Level Calibration
The Audio Riser requires calibration so that the level of the audio signal at the end of the Audio
Riser is 0dBm (0.77Vrms). To achieve this, follow the following steps:
1. At the originating point of the Audio Riser, place the calibration potentiometer to midrange.
2. Make sure the 4100U/4100ES Analog Audio controller is playing the 1KHz supervision tone.
3. Ensure that the Audio Riser is properly terminated. Measure the audio.
4. The end of the Audio Riser is the last AMP-96 Amplifier connected to the riser.
•
For 1-10 AMP-96 Amplifiers connected to the riser, use the 750 Ohm (P/N 976448)
termination resistor.
•
For 11-20 AMP-96 Amplifiers connected to the riser, use the 4.7k Ohm (P/N 976449)
termination resistor.
•
For 21-25 AMP-96 Amplifiers connected to the riser, no termination resistor is required.
5. Measure the riser signal level at the end of the riser (or riser subsection) by measuring the AC
voltage at terminals TB2-1 and TB2-2 of the AMP-96 Amplifier or at the TB1-1 and TB1-2 or
TB2-1 and TB2-2 of the CS2 Channel Select Board.
6. Adjust the RISER GAIN potentiometer R1, on the Audio Interface board so that the voltage
measured at the end of the riser is 0.77VRMS (+/- 0.07V).
Introduction to TFX Audio Interface Module,
Continued
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