GTS 100X - JBL Car Audio User Guide / Operation Manual. Page 27

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27
grounding the source unit and/or 
amplifier directly to the battery
will provide the best results,
although, usually, this provides
the worst results with most cars.
In complex systems involving
components from different man-
ufacturers, it helps to know the
type of power supplies used in
each component. For low-level
signal processors such as equal-
izers or electronic crossovers, a
manufacturer may either use a
power supply which is isolated
through a DC-to-DC converter, or
a simple regulated supply from
the 
+
12V vehicle battery.
Components using the latter type
of supply can be identified by a
direct connection from power
ground to the shield of the RCA
jacks (measured with no other
connections present). For these
components, the best ground con-
nection may be one where the
power ground wire is not con-
nected at all! The RCA cables
will provide the ground connec-
tion to the source unit. Please
note that this is only appropriate
for units which draw less than
500mA of current. Higher power
units of this type are best con-
nected 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 supplies. 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
(>AWG10). Do not connect
this to the vehicle’s wiring har-
ness, but go directly to a metal
part of the vehicle.
2. Connect all non-isolated signal-
processor grounds directly to
the head unit chassis at the
same point. Run each wire
individually. Due to wire resis-
tance, connecting multiple
wires to a single wire, then
running the single wire to the
head unit, is not the same!
3. Connect all amplifier and iso-
lated signal processor grounds
directly to the vehicle chassis
at the same point as each
other, 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 sup-
ply noise can enter the system
through the head unit power sup-
ply or the supply of an equalizer
or other signal processor. Putting
a filter on the head unit or signal
processor power supply input
may then be helpful.
GTS100x OM  7/16/98 2:56 PM  Page 27
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