Notifier AFP-300 Installation Manual page 136

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The ACT-1 Audio Coupling Transformer couples low-level audio to audio amplifiers or
other audio inputs, such as the ATG-2. An ACT-1 can be used to couple a low-level
audio signal to up to eight devices in the same cabinet. It provides electrical isolation
between low-level audio riser and equipment to which the signal is to be fed (amplifiers
or the ATG-2). Also, the ACT-1 provides common mode noise rejection (CMNR),
greatly reducing crosstalk from Signaling Line Circuits.
You can install the ACT-1 in any application that uses AA-30, AA-100, or AA-120
audio amplifiers, subject to the following restrictions:
• The amplifiers must mount remotely from the source of low-level audio devices,
such as an AMG or ATG.
• The power supplies in the main control panel cabinet and the remote cabinets do
not share the same common.
• Ground fault is enabled on each power supply.
Isolated power supplies, each with respective ground fault detection circuits enabled,
are often used to aid the quick location of ground faults in large systems. This task is
more difficult if the entire system (main and all remote devices) share the same
common and the power supply in the main control panel cabinet provides ground fault
detection.
In larger systems, capacitance becomes a critical factor in creating sporadic and
difficult-to-find ground faults along a single common connection. In these systems—as
in systems that expand—use an ACT-1 if possible.
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For example, take a system consisting of a remote annunciator powered from a local
supply within the same cabinet—but connected through an EIA-485 circuit—to the
main control panel (Figure 4-42). A common connection occurs (although a poor one)
along the EIA-485 interface. Therefore, the power supplies in this system are not
adequately isolated and problems will occur. In this case, the earth fault detection of
the remote power supply must be disabled and a good common connection must be
made between the two systems. An ACT-1 is not required for amplifiers mounted in
this remote cabinet but installation of an ACT-1 can reduce CMN from the SLC.
Figure 4-42 shows a block diagram of a remote annunciator powered from a local
power supply:
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AFP-300/AFP-400 Installation PN 50253:C1 05/22/97