JBL Grand touring series User Manual page 34

~ be one where the power ground
34
wire is not connected at all! The
RCA cables will provide the
ground connection to the source
unit. Please note that this is only
appropriate for units that draw
less than 500mA of current.
Higher power units of this type,
such as amplifiers, are best ser-
viced with their ground wires
connected directly to the chassis
of the head unit.
The trickiest grounding task is
created when some components
of this type are mixed with other
components using isolated SUP-
plies. For this type of system, the
following grounding scheme will
usually work:
1. Connect the head unit chassis
to a solid vehicle ground using
a short, heavy-gauge wire (see
recommended minimum and
maximum wire sizes in the
specifications section). Do not
connect this to the vehicle's
wiring harness, but go directly
to a metal part of the vehicle.
2. Connect all signal-processor
grounds directly to the head
unit chassis at the same point.
Run each wire individually.
Due to wire resistance, con-
necting multiple wires to a
single wire, then running the
single wire to the head unit, is
not the same!
3. Connect all amplifier grounds
directly to the vehicle chassis
but not necessarily to the same
point as the head unit.
Power-line noise - The built-in
power supply filter of the ampli-
fier makes external filters unnec-
essary. In some cases, power
supply noise can enter the system
through the head unit power SUP-
ply or the supply of an eaualizer
or other signal processor. Putting
a filter on the head unit or signal
processor power SUPPIY input
may then be helpful. Using a
portable powered speaker as
described in the "Source Noise"
section can help YOU isolate an
individual component that may
be sensitive to this. Start at the
head unit and work back, check-
ing each component individually.
Power wires carrying high cur-
rents may induce noise in nearby
signal wires. Make sure that
power wires and signal wires do
not run together for long dis-
tances. When power and signal
leads must cross, they should
cross at right angles. If YOU sus-
pect that power line noise is
being induced in the signal leads,
you can repeat the test for source
noise described previously, but
perform the test at the amplifier
end of the signal cables. One
power wire that it will be impos-
sible to stay away from is the
vehicle chassis. The chassis is
one giant ground wire! Use hish-
quality shielded cables or a bal-
anced-line system for the Ions
front-to-rear signal runs to
reduce the likelihood of noise
pickup from this source.
Other Noise Sources - Common
noise problems will be solved by
proper grounding and power SUP-
ply connections. However, there
are impulse type noise sources
that may require suppression at
the noise source. Many noise sup-
pression devices (such as spark