Selecting Stereo, Parallel, Or Bridge Mode; Setting Low Frequency Filters - QSC ISA 280 User Manual

Selecting Stereo, Parallel, or
Bridge Mode
The amplifier can be set for normal Stereo
mode, Parallel Input mode, or Bridge Mono
mode.
Stereo Mode- Each channel remains inde-
pendent, and may be used for two different
signals.
Parallel Mode - This setting connects
both inputs together. One signal feeds both
channels. Each channel's Gain control and
speaker connection remain independent.
Bridge Mode- This setting combines both
channels of a pair into a single channel
with twice the output voltage. Use only the
first channel's input and Gain control. Set
the second channel's Gain control at mini-
mum. The load must be rated for the higher
power (or voltage) and is connected as
shown on pages 6 and 7.
Do not connect more than one
input when operating in parallel
or bridge mode.

Setting Low Frequency Filters

ISA 280, ISA 450, ISA 750 and ISA 1350:
Use of the Low Frequency Filters is recom-
mended. Use the appropriate switch set-
tings to turn the filter ON or OFF and to
select the filter frequency. When set to the
ON position, the channel has a 12dB per
octave Low Frequency filter to limit subau-
dio cone movement, making more power
available for the loudspeaker's rated fre-
quency range. The filter should only be
turned OFF for driving subwoofers.
ISA 300Ti, ISA 500Ti, and ISA 800Ti: The
Low Frequency Filters are always active
and not defeatable. Each channel has a
12dB per octave Low Frequency filter to
prevent saturation of the 70V loudspeaker
transformers. This reduces distortion and
prevents amplifier overload. The 50 Hz set-
ting usually works well with high quality
loudspeaker transformers. The 75 Hz set-
ting works well with speech-grade loud-
speakers and transformers.
ISA 280/450/750/1350
Stereo Mode -
Switches 4, 5, 6 and 7
are all set to the LEFT
position.
Parallel Mode -
Switches 4 and 5 are
set to the RIGHT posi-
tion.
Switches 6 and 7 are
set to the LEFT posi-
tion.
Bridge Mode-
Switches 4, 5, 6, 7, and
8 are all set to the
RIGHT position.
Switch 10 is set to the
LEFT position.
Low Frequency Filter-
Switches 2 and 3 con-
trol CH1. Switches 8
and 9 control CH2.
Switches 3 and 8 turn
the LF filter ON or OFF.
Switches 2 and 9
select 30Hz or 70 Hz.
ISA 300Ti/ 500Ti/800Ti
Ti Stereo Mode -
Switches 3, 4, 5, 6, 7,
and 8 are all set to the
LEFT position.
Ti Parallel Mode -
Switches 3, 4, and 5
are set to the RIGHT
position.
Switches 6, 7, and 8
are set to the LEFT
position.
Ti Bridge Mode-
Switches 3, 4, 5, 6, 7,
and 8 are all set to the
RIGHT position.
Switch 10 is set to the
LEFT position.
Ti Low Frequency Filter-
Switch 2 controls CH1.
Switch 9 controls CH2.
Switches 2 and 9 select
50Hz or 75 Hz.
EN
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