JL Audio HD900/5 Owner's Manual page 8

bridging Considerations
Bridging is the practice of combining the
output of two amplifier channels to drive a single
load. When bridged, each channel produces
signals of equal magnitude, but opposite polarity.
The combined output of the two channels
provides twice the output voltage available from a
single channel. The HD900/5 has been designed
for bridging of its two main channel pairs without
the need for input inversion adaptors.
The mono subwoofer channel cannot be
bridged to another mono channel.
To bridge either pair of main channels, use the
"Left +" and "Right –" speaker connectors only
(the "Left –" and "Right +" remain unused).
Then connect a mono signal to both left
and right RCA inputs for that channel pair.
This requires an RCA "Y-Adaptor" (sold
separately), because a bridged pair of channels
requires that both amplifier channels of the
bridged pair receive input. Connection of
only one RCA input will result in reduced
power output, increased distortion and
can cause the amplifier to overheat.
When bridged, each channel pair will
deliver optimum power into a 3-8Ω load.
Operating bridged channel pairs into a load
lower than 3Ω is not recommended.
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speaker Connector Plugs
There are three speaker connector plugs on the
HD900/5: one for the front channels, one for the
rear channels and one for the subwoofer channel.
To connect the speaker wires to the amplifier,
unplug the speaker connector plugs from the
amplifier chassis (pull back firmly) and back out
the set screws on each connector plug, using the
supplied 2.5 mm hex wrench. Strip 3/8 inch (10
mm) of insulation from the end of each wire and
insert the bare wire into the receptacle on the
speaker connector plug, seating it firmly so that
no bare wire is exposed. While holding each wire
in place, tighten each set screw firmly, taking care
not to strip the head of the screw.
Speaker loads below 1.5Ω nominal per channel
in stereo or 3Ω nominal in bridged mode are
not recommended and may cause the amplifier
output to distort excessively.
"status" led / ProteCtion CirCuitrY
There is a single multi-color LED on the
control panel of the amplifier to indicate the
amplifier's operating status. This LED's behavior
is as follows:
1) Flashing Green: amplifier is powering up,
audio output is muted.
2) Constant Green: amplifier is on and
functioning normally, audio output is active.
3) Constant Red: lights to indicate that the
amplifier has exceeded its safe operating
temperature, putting the amplifier into a self-
protection mode, which temporarily reduces
the peak power output of the amplifier. The
red light will turn green and the amplifier will
return to full-power operating mode when its
temperature returns to a safe level.
3) Constant Amber (yellow): lights to indicate
that at least one channel is in overcurrent
protection mode. This could mean that the
impedance of the speaker load connected to
the amplifier is lower than the optimum load
impedance range for the amplifier. When this
light is on, a protection circuit engages and
reduces the power output of the channel(s)
experiencing the problem. This can manifest
itself as audible distortion.
The amber indicator will also light when
a short-circuit is detected in the speaker
wiring (this can be a short between the
positive and negative speaker wires or
between either speaker wire and the vehicle
chassis). This can be used to diagnose a
short-circuit by only connecting one of the
amplifier sections at a time ("Front" or
"Rear" or "Sub" channels). The amber LED
will light when you connect the section that
is experiencing the problem and turn the
volume up. Note that a short in the speaker
wiring may show an alternating red/green
status light with no signal (volume down).
4) Alternating Red and Green: lights to indicate
that the amplifier is experiencing a fault
that may require service of the amplifier, its
wiring or the vehicle's charging system. Audio
is muted when this fault occurs. The most
likely cause of this fault is a low supply voltage
condition. If battery voltage drops below 8.5
volts at any point, the amplifier (except for
the "Status" LED) will shut itself off to protect
itself and the vehicle's charging system. If the
Remote Turn-On voltage drops below 6 volts,
the "Status" LED will also turn off.
The amplifier will turn back on automatically
when voltage climbs back above 9 volts. This
shut-down and turn-on behavior may happen
in a rapid cycle when bass-heavy program
material causes a weak charging system to
momentarily dip too low. If this is happening
in your system, have your charging system
inspected to make sure it is working properly.
If no problem is found with the supply voltage
to the amplifier and you are still seeing
alternating Red and Green on the "Status"
LED, check that there are no short-circuits to
chassis ground in any of the speaker wiring
in the vehicle. Disconnect speaker connectors
from the amplifier one-by-one to check.
If no problem is found with the supply or
remote voltage, disconnect everything except
power/ground/remote. If the amplifier is then
turned on and displays an alternating red-
green, the amplifier needs service.
For more information on troubleshooting this
amplifier, refer to Appendix D (pages 20, 21).
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