either subwoofer or component
speakers in a bi-amplified system,
or conventional full-range speakers
The GTS300 and 600 also include
preamp-level outputs which can
provide either full-range, high-pass
or low-pass signal to drive
additional amplifiers. This lets you
build systems of virtually any
design without requiring a
separate electronic crossover.
Although the GTS300 and GTS600
are designed to make installation
as easy as possible, they are
sophisticated products that require
proper installation to realize their
full performance potential.
If you feel you do not have the
necessary knowledge and skills we
strongly recommend that the
installation be done by your
If you choose to install the GTS300
information in this manual
you start the installation.
Pay particular attention to the
safety precautions and notes.
Refer to the “Crossover Frequency
Adjustments” and “Speaker Level
Input Impedance Adjustments”
sections of this manual to see if
you will need to make alterations
to their factory settings. If you are
not using the built-in crossover, or
the speaker level inputs, you may
1. Disconnect the negative cable
Note: If the
vehicle’s radio features a code
type security system, make
certain you know the code
Thanks for purchasing your new
GT series automotive amplifier.
The GT series amplifier you have
chosen includes many unique
features to enhance its perfor-
mance and utility. The power amp-
lifier circuitry is a fully discrete
design notable for its low dis-
tortion and unusually clean and
clear sound quality. Your GT series
amplifier will easily connect to
virtually any car audio system,
whether it is factory installed or
one purchased separately.
In addition to conventional
preamplevel inputs, this model
features JBL’s Universal Interface
design, which facilitates simple
connection to factory radios with
the low distortion that is usually
only associated with preamp level
connection. With Universal Inter-
face, a factory radio can be used
either as the main music source or
combined with a CD player or
changer, which includes volume
control capability, simultaneously
connected to the amplifier. By
providing this two-unit direct
connection, Universal Interface
circuitry eliminates the need for an
FM modulator to interface a CD
player to factory radios, improving
the fidelity of digital playback.
In addition, when using a high-
powered (BTL) radio through the
speaker-level inputs, Common
Sense turn-on circuitry senses the
common-mode voltage present on
the radio’s speaker wires, turning
the amplifier on without an
additional “remote” wire.
Also, the built-in active crossover
provides either full-range, high-
pass or low-pass operation. This
lets your GT series amplifier power
