1. Introduction
1.1Thanks for purchasing your new GT series automotive multi-channel amplifier. Your GT series amplifier will easily connect to virtually any car audio system, whether it is factory installed or purchased separately. The GTQ360 and GTQ240 include an abundance of unique features which are described in this man- ual. The flexible design of their built-in crossover circuitry allows elaborate sys- tems to be built more simply than with conventional components. For optimum performance, the power amplifier circuit- ry is a fully-discrete design notable for its low distortion and unusually clean and clear sound quality.
In addition to conventional preamp-level inputs, the GTQ360 and GTQ240 feature JBL’s Universal Interface™ design, which facilitates simple connection to factory radios with the low distortion that is usu- ally only associated with preamp level connection. With the Universal Interface on the GTQ360 and GTQ240, a factory radio can either be used as the main music source or simultaneously com- bined with a CD player or changer that has volume-control capability. By provid- ing 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 pres- ent on the radio’s speaker wires, turning the amplifier on without an additional remote wire.
Also, the built-in active cross-over pro- vides either full-range, high-pass or low- pass operation. This lets your GT series amplifier power either subwoofer or com- ponent speakers in a bi-amplified system, or conventional full-range speakers in simpler systems.
The GTQ360 and GTQ240 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 elec- tronic crossover.
1.2 About Installation
Although the GTQ360 and GTQ240 are designed to make installation as easy as possible, these are extremely sophisticat- ed products that require proper installa- tion and setup to realize their full perfor- mance potential. If you feel you do not have the necessary knowledge and skills,
we strongly recommend that the installa- tion be done by your authorized JBL deal- er.
If you choose to install the GTQ amplifier yourself, read all of the information in this manual before you start the installation.
Pay particular attention to the safety pre- cautions and notes.
2. Installation and Use
2.1Refer to the “Speaker-Level Input Impedance Adjustments” and “Crossover Frequency Adjustments” sections of this manual (page 7) to see if you will need to make alterations to the factory settings. If you are not using the built-in crossover, or the speaker-level inputs, you may skip this step.
1. Disconnect the negative cable from the battery. Note: If the vehicle’s radio fea- tures a code-type security system, make certain you know the code before discon- necting the battery!
2. Run a power cable complete with a fuse (not included) directly from the posi- tive +12V battery terminal to the desired amplifier location. Keep the fuse within 6" of the battery terminal, and position it before the wire runs through any metal partition. A minimum of #10AWG is required for the GTQ240 and #8AWG for the GTQ360. The GTQ240 requires a 30A fuse, the GTQ360 a 60A fuse.
Note: All wiring connections should be made either by soldering with heatshrink tubing insulation, by using commercially available high-quality distribution blocks, or with high-quality crimp-type insulated connectors installed with a professional- type, articulated crimping tool. Soldering crimp-type terminals is recommended for additional security. Never use wire nuts, insulation-displacement connectors (i.e., ScotchLok type), or twist and tape con- nections. Do not use electrical tape; it will loosen with age and extreme temperatures.
3.Mount amplifier in the desired location using the included screws.
4.Connect power wiring as shown in the Wiring Diagram.
5.Connect the outputs from the head unit to the appropriate inputs of the amplifier according to the Wiring Diagram with either (or both) high-quality low-level sig- nal cables with RCA plugs, or the supplied speaker-level input connector.
6.Connect the speakers to the amplifier according to the Wiring Diagram.
7.Turn the gain controls to the
1/4-position for all groups.
8.Set the bass boost of each group to the desired position.
9.Set the crossover switches for each group as desired.
10.Set the Group 2 Input as desired.
11.Set the mode switches to Stereo,
Left + Right, or Left Input Only operation for each group.
12.Double-check your switch settings. Reconnect the negative battery cable. Note: Incorrect switch settings can dam- age your speakers!
13.Turn on the signal source at a low vol- ume level, and check for the correct out- put from each speaker.
14.Adjust the amplifier gain controls using the procedure described in the “Adjusting the Gain” section.
15.Read the rest of the manual to get maximum use and enjoyment from your amplifier.
