12
Audio Connections
The inputs and outputs are fully balanced on XLR connectors and are wired conventionally with pin
1 as ground. Because the system is fully floating, either pin 2 or pin 3 can be designated as hot
(phase ) so long as the same protocol is adhered to for both inputs and outputs. To comply with
EMC regulations filtering is incorporated into this unit. To maximise the benefits of this it is recom-
mended that the XLR shell is not connected to the audio ground.
DC Operation
This unit is designed primarily for operation from the mains supply. The DC connection is intended
for use as a backup power for evacuation and similar uses in conditions of mains failure. Upon
failure of the mains supply, as the unit is already operational the DC supply is only required to
furnish the current necessary to maintain operation, nominally 200mA at 24V.
If it is required to power the unit only from the DC supply, this is quite acceptable but the power
supply MUST be capable of providing an initial 1.5A start up current to initiate the switched mode
power supply. The duration of this current draw is only for approximately 5 milliseconds after which
the current drops to 200mA. This is no problem when running from batteries but could overload a
bench power supply. Please refer to the application note later in the manual for a method of starting
and running from a supply that only gives 250-300mA .
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