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5

(+)

(–)

(+)

(–)

Parallel Wiring

Series Wiring

2 ohms
Nominal
Impedance

8 ohms
Nominal
Impedance

4 ohms

4 ohms

4 ohms

4 ohms

• The remote power control system turns
the GTQ amplifier off when not in use to
prevent discharging of the vehicle’s bat-
tery. Because the JBL GTQ amplifiers
include Common Sense 2-way turn-on,
when using the speaker-level inputs with
a head unit that includes a BTL power
amp it is not necessary to connect the
remote wire. The amplifier will automati-
cally activate whenever you turn on the
head unit. If you are using the line-level
inputs, or the speaker-level inputs with a
head unit that does not have a BTL power
amp, use the following remote wire con-
nections.
• Using the REM-IN feature – When 

+

12

volts is applied to the remote IN/OUT ter-
minal the amplifier is turned on. A red
LED on the top panel of the amplifier will
illuminate to indicate the amplifier is on.
If the head unit has a 

+

12 volt automatic

antenna or amplifier remote activation
wire, connect it to the REM-IN/OUT con-
nector on the GTQ amplifier. When the
amplifier is turned on, there is a time
delay of several seconds (longer in cold
weather) before the amplifier will produce
sound. This eliminates the chance of
annoying noises produced by the radio or
signal processors being amplified and
passed to the speakers when the system
is first activated.
• Some head units have no automatic
antenna or power amp activation wire.
Others have automatic antenna wires that
are “on” only when the radio is used but
not when a tape is played. In such cases,
connect the remote-in turn-on terminal to
an unused accessory terminal in the fuse
block, or any other 

+

12 volt source that is

turned on and off with the vehicle’s igni-
tion switch. The remote on/off system 

The low-level preamp outputs of any
radio/tape deck, CD player, or preamp/
equalizer so equipped can drive the
GTQ360 or GTQ240. The gain controls of
the amplifier are used to match its input
sensitivity to the output voltage of the
source. This matching is important to
keep noise low and is explained in the
“Adjusting the Gain” section of this 
manual.
Thanks to Universal Interface Circuitry,
the GTQ360 or GTQ240 can also be con-
nected to power amplifiers, radios or
equalizers that are equipped with only
speaker outputs by connecting them
through the speaker-level input connec-
tor. Inside the GTQ360 and GTQ240, the
speaker-level and preamp-level inputs are
connected through a mixing circuit, which
allows them to be used simultaneously.
Therefore a low-level source, such as a
CD player equipped with a volume con-
trol, may be connected to the preamp-
level inputs at the same time as a pow-
ered radio/tape unit is connected to the
speaker-level inputs. This provides a high-
er performance alternative to an FM mod-
ulator connection when you wish to add
CD capability to a factory cassette stereo.
Switching from one source to the other is
as simple as turning the desired source
on and turning the undesired one off —
no additional switches or relay connec-
tions are needed.

Proper wiring of the GTQ amplifiers and
the associated components is extremely
important for proper performance and
long-term reliability. Using the proper
type of wire is very important.
Route the wiring through the car carefully.
Do not allow wires to lay against sharp
sheet metal edges or any other surfaces
that might wear away or cut through the
insulation of the wire. Use insulated strain
reliefs, rubber grommets and plastic tub-
ing to protect the wires whenever they are
run through sheet metal panels or are
placed where they might be pulled or
damaged.

• Proper grounding is extremely impor-
tant. Use a heat- and oil-resistant stranded
copper automotive wire equivalent to the
size used for the 

+

12V connection. Crimp

or solder and insulate any wire-to-wire
connections. Keep the ground wire as
short as possible. A ground wire must be
solidly connected to a major sheet-metal
structure of the vehicle such as a panel
near the amp-mounting location. Scrape
all paint and primer off the sheet metal at
the grounding point to ensure a good
electrical connection. Attach the wire to
the grounding point with a nut, bolt and
star washer. The high current demanded
by high-powered amplifiers requires a
more secure ground than the typical
sheet-metal screw will provide. Coat the
connection with silicon sealant for better
long-term reliability.

GTQ 360 new  7/17/98 10:44 AM  Page 5

6

Cassette/CD Tuner

CD Player

or Changer

CD Input

Cassette/CD Preamp Output

Antenna Input

Power
Antenna

Power

Antenna

Relay

Blue w/White Stripe - Remote On/Off

Main +12V

Power Ground

Chassis Ground

Vehicle Battery

–

+

Ignition Switch

Antenna

Motor

Power

Supply

Blue (Blue/White)

Remote On/Off

Remote Antenna

Black - Power Ground

Red - Main +12V

Yellow - Back Up Power

Fuse

Fuse

Fuse

Cassette/Receiver

Power Supply

Wires

Speakers

+

–

+

Speakers

+

–

+

(Not Included)

Amplifier

Power

Connection

Amplifier
Speaker
Output
Connection

Amplifier
Speaker
Output
Connection

Amplifier
Speaker
Output
Connection

Amplifier

Speaker

Level

Inputs

Cassette/CD Tuner 
Speaker-Level Output Connection
(Use only when line-level output
is not available)

draws negligible current so a relatively
small (18 or 20 gauge) wire may be used.
• Using the REM-OUT feature – The REM-
IN/OUT terminal of the GTQ amplifier
may be used to turn on other amplifiers
when the GTQ amplifier is being turned
on by the Common Sense circuitry in the
speaker-level input. Simply connect the

head unit speaker-level outputs to the
GTQ amplifier speaker-level inputs and
connect the REM-IN/OUT terminal to the
remote-in terminal of other amplifiers or
signal processors. The GTQ amplifier will
turn on the other amps or processors
whenever the Common Sense circuitry
turns on the GTQ amplifier.

High-Pass Satellite 
Crossover Frequency: 100Hz

C:

300

µ

F capacitor

100V, non-polarized

Subwoofer Low-Pass
Crossover Frequency: 100Hz

L:

6.2mH air core inductor

(+)

(+)

(–)

(–)

(+)

(–)

C

Subwoofer (Low-Pass)

Tweeter/Midrange Satellites

(High-Pass)

Right

Left

C

L

GTQ360

A. Satellite/Subwoofer

Stereo, Non-Bridged
Speaker Connection*

Center Channel

Bridged Speaker Connection*

* Center Channel Speaker Minimum 8 Ohms, Main
Speakers Minimum 4 Ohms When Used Simultaneously.

8 

Ω

 L-Pad

(Optional but Recommended)

4

Ω

 Minimum

4

Ω

 Minimum

GTQ360

(+)

(–)

(+)

(+)

(–)

(–)

8 

Ω

 

Minimum

B. Center Channel

*You may change the subwoofer satellite crossover frequency by using the 

Inductor and Capacitor values calculated with the following formulas:

High-Pass (Satellite Crossover):                                                                   = New Capacitor Value in 

µ

F

Low-Pass (Subwoofer Crossover):                                                                = New Inductor Value in mH

30,000

Desired crossover Frequency in Hz

620

Desired crossover Frequency in Hz 

30A

30A

GR1

R        GR1        L

LINE LEVEL

INPUT

SPEAKER LEVEL INPUTS

SPEAKER OUTPUTS (BRIDGED: R+TOL–)

POWER

GR2

GR1

GR2

BATT(+)

GND

MUTE

FUSE

30A

FUSE

30A

REM

IN/OUT

L

+ –

– +

+ –

– +

+

+

–

–

–

–

R

PREAMP

OUTPUTS

R        GR2        L

L             GR1            R

+

+

L             GR2            R

30A

30A

GR1

R        GR1        L

LINE LEVEL

INPUT

SPEAKER LEVEL INPUTS

SPEAKER OUTPUTS (BRIDGED: R+TOL–)

POWER

GR2

GR1

GR2

BATT(+)

GND

MUTE

FUSE

30A

FUSE

30A

REM

IN/OUT

L

+ –

– +

+ –

– +

+

+

–

–

–

–

R

PREAMP

OUTPUTS

R        GR2        L

L             GR1            R

+

+

L             GR2            R

Simultaneous Stereo-Mono Connection Diagrams

GTQ 360 new  7/17/98 10:44 AM  Page 6

7

The speaker level inputs of the GTQ
amplifiers come factory-set with
100k ohm input impedance. This will pro-
vide the lowest distortion operation from
the speaker outputs of most modern head
units by reducing the power the amplifier
in the head unit must deliver to practi-
cally, nothing. On some older or lower-
priced head units this load will not facili-
tate proper fader operation. To allow for
this, we have provided the ability to
change the input impedance of the speak-
er-level inputs to 15 ohms. This is accom-
plished by moving the jumpers shown on
the diagram below. This input is also
capable of directly accepting signals,
when in the 100k ohm setting, from many
Balanced Line Drivers such as those
sometimes used in competition vehicles.
If the head unit has 4 channels of built-in
amplification and/or an electronic fader
control, you should leave the jumpers in
the factory-set position.
If the head unit has 2 channels of amplifi-
cation, with a speaker-level fader, the
jumpers should be set to the 15-ohm
position. This will always be a rotary-type
control, not one controlled by electronic
pushbuttons.

15

Ω

100K

REM
OUT

30

30

GND

BAT

LINE INPUT

JUMPER SELECTOR

SELECT 100K OR 15 OHMS

The GTQ amplifiers include built-in 
frequency selectable crossovers. One
crossover is connected in series with the
amplifier circuitry and the other cross-
over is connected to the preamp level out-
put jacks. These crossovers can be set in
either the “F” (full bandwidth operation),
“L” (subwoofer operation), or “H” (satel-
lite operation).
The crossover frequencies are set by
chips inside the amplifier. These chips are
simply a set of resistors, connected
across the pins and molded into a single
package. The crossover frequencies may
be changed to any value desired by
changing the resistor network. JBL has
chips available in the popular values list-
ed in the table which follows. If none of
these suit your system, you may purchase
compatible resistor networks from a local
electronics store, or you may build your
own custom values from discrete resis-
tors mounted on a 14-pin DIP Header
using the instructions which follow.

50Hz

47k 

Ω

1-23-750

80Hz

33k 

Ω

1-23-817

120Hz

22k 

Ω

1-23-820

200Hz

12k 

Ω

1-23-821

250Hz

10k 

Ω

1-23-810

375Hz

6.8k 

Ω

1-23-822

500Hz

4.7k 

Ω

1-23-815

650Hz

3.9k 

Ω

1-23-823

2.5kHz

1k 

Ω

1-23-824

5kHz

470 

Ω

1-23-816

Regardless of whether you build or buy it,
the necessary resistor network has the
following configuration:

• Each resistor in the package has the
same value.

• If you know the crossover frequency you
want, you can calculate the resistor value
necessary by solving the following equa-
tion:

• Use the following equation if you have a
resistor pack of a known value, and want
to find its crossover frequency:

• To build chips from discrete resistors,
solder the resistors to a standard 14-pin
“DIP Header” according to the diagram. If
a DIP Header is not available, you may
bend the leads of 1⁄4-watt resistors 90
degrees, trim them to 3mm-length, and
insert them directly into the chip sockets.

The GTQ amplifier includes a mute input
terminal. This amplifier will mute when a
5V to 12V DC signal is applied to the
“mute” input and will be in normal oper-
ation mode with either a ground or noth-
ing connected to the “mute” input. This
“mute” input is compatible with any
aftermarket noise gate that puts out a
control voltage of 

+

5V to 

+

12V DC.

Group 1 Left (

+

):

White

Group 1 Left (–):

White with 
Black Stripe

Group 1 Right (

+

):

Gray

Group 1 Right (–):

Gray with 
Black Stripe

Group 2 Left (

+

):

Green

Group 2 Left (–):

Green with 
Black Stripe

Group 2 Right (

+

):

Purple

Group 2 Right (–):

Purple with 
Black Stripe

2,500,000

Frequency in Hz

2,500,000

Resistor Value in ohms

GTQ 360 new  7/17/98 10:44 AM  Page 7

8

To change the crossover frequency
change the resistor network as follows:
1. Remove the screws from the bottom
panel as shown below.

2. Select which resistor module, high
pass or low pass, that you wish to
change.
3. A chip puller, which can be obtained
from any electronics store, is recom-
mended to remove the resistor chip. Pull
the resistor chip from the socket as
shown in the figure below.

4. Place the new module in the socket
making sure all pins are lined up with the
socket holes. Press the module firmly into
the socket.
5. Replace the bottom lid.
For further information on how to use the
speaker output and preamp output
crossovers for system building see the
“Typical Applications” and “Add-On and
Upgrade Steps” sections.

HIGH PASS

FILTER
FREQUENCY

SELECTION

MODULE

LOW PASS

FILTER
FREQUENCY

SELECTION

MODULE

C10

C13

JBL INC.

NORTHRIDGE, CA

JBL GTS600

PC00108800

REV A

CROSSOVER

Before operating the GTQ amplifiers,
recheck all wiring connections to make
sure they are correct and secure. Be sure
that a fuse (not included) is installed in the

+

12V line near the battery. Reconnect the

negative ground (–) terminal of the bat-
tery. Make sure that the mode switches,
crossover switches, Group 2 Input switch-
es, and crossover frequency modules are
properly set.
• The setting of the gain controls on the
GTQ amplifiers is important to ensure
proper performance, low noise levels, and
maximum reliability in the system. 
Using a high signal level from the source
and a low gain setting on the amplifier
will help keep background noise levels in
the system low.
• To adjust a system using a single GTQ
amplifier, start with both of the amplifier
gain controls fully counterclockwise. Set
all bass/treble or equalizer controls to
their centered or bypassed positions.
While listening carefully to the system
output, adjust the volume control of the
radio/tape deck to the point where you
first begin to hear audible distortion. 
Use caution: excessive distortion can
damage loudspeakers. Reduce the level
just to the point where the distortion goes
away. If this setting does not provide ade-
quate volume levels, gradually increase
(turn clockwise) the gain control for the
main (usually front) speaker groups on
the GTQ amplifier until the system plays
as loud as necessary or when the first
signs of distortion are heard.

Active 3-way using outboard tweeter amplifier

GR 1

GR 2

GR 1

Pre Out

GR 2

Input

GR 2

Pre Out

GR 1

Input

Input

Midbass

Tweeters

Front

Subwoofers*  

  * A single (mono) subwoofer may be used by setting GR 2 
    mode to "L+R."
** The crossover frequencies listed are suggestions. Actual 
    crossover points should be determined from 
    loudspeaker requirements.

,,

,

,

The following diagrams show the most
common basic system configurations of
the GTQ amps. One or more of these
building blocks may be combined to form
elaborate system designs. 
The GTQ amps use the terminology
“Group 1” and “Group 2” to indicate the
two main signal paths within the amplifi-
er. Each “group” may consist of a mono
bridged signal or a stereo pair of L+R 
signals depending on the system 
configuration.

AIR FLOW

BEST-Vertical Mounting

AIR FLOW

GOOD-Horizontal Mounting

NEVER-Mount Upside Down

GTQ 360 new  7/17/98 10:44 AM  Page 8