Page 1
4-Channel Amplier Owners Manual
GT-475
GT-4100
Page 2
Introduction
Thank you for choosing Boston Acoustics®and congratulations on your purchase of the
Boston GT
performance and ease-of-use of the GT Amplifier should come as no surprise. If you’re
new to Boston, welcome – you’ve made a great choice.
®
Amplifier. If you own other Boston products, the outstanding audio
Table of Contents
Parts list 3
Specifications
Connections 4
Top panel removal / installation
Table Of Contents
Controls 5
Status LEDs
Installation - General 6
Before you install
Battery and charging system
Wire routing
Mounting location
Passenger & trunk compartment mounting
Multi-Position Mounting Feet
Venting
Installation - Wiring 7
Amplifier fuses
Wire gauge
Power 12v and ground (GND) connection
Remote input connection
Speaker output connection
Mono subwoofer operation
Tuning The Amplifier - Front and Rear Speakers 8
Music
Front signal routing switch
Input sensitivity control
Highpass and lowpass crossover controls
Head unit
Volume
4-channel highpass operation switch configuration diagram
Input sensitivity control
Crossover controls
Q-Tune
4-channel operation wiring configuration diagram
™
control
Tuning The Amplifier - Front Speakers and Subwoofers 10
Front signal routing switch
Head unit
Volume
Input sensitivity control
Highpass crossover control
Q-Tune
Rear input switch
Lowpass crossover control
GT-RSL
Bridged operation wiring configuration diagram
Amplifier Troubleshooting Guide 12
Service Information
22
™
control
Page 3
Parts List
Included Hardware: GT-475 GT-4100
Installation Manual 1 1
Female Quick-Connect Terminal 1 1
(for remote turn-on input)
2mm Hex Wrench 1 1
3mm Hex Wrench 1 1
Mounting Screws 4 6
Specifications
Technical Specifications: GT-475 GT-4100
Rated Power (CEA-2006-A):
@ 4-Ohm (Stereo): 75 Watts x 4 100 Watts x 4
@ 2-Ohm (Stereo) 120 Watts x 4 150 Watts x 4
@ 2-Ohm (Mono) 250 Watts x 2 450 Watts x 2
Parts And Specifications
Mixed Operation (CEA-2006-A):
@ 4-Ohm (Stereo) & 2-ohm (Mono): 75 W x 2, 250 W x 1 100 W x 2, 450 W x 1
Rated Power (12v):
@ 4-Ohm (Stereo): 65 Watts x 4 85 Watts x 4
@ 2-Ohm (Mono) 200 Watts x 2 330 Watts x 2
Frequency Response (-3dB): 10Hz–95kHz 10Hz–95kHz
Signal-to-Noise Ratio (A Weighted): >100dB >100dB
THD+N: 0.03 0.03
Highpass Crossover:
Frequency Range: 20Hz - 350Hz 20Hz - 350Hz
Slope (dB Per Octave): 12dB 12dB
Lowpass Crossover (Rear Channel Only):
Frequency Range: 50Hz - 350Hz 50Hz - 350Hz
Slope (dB Per Octave): 12dB 12dB
Signal Voltage Input Range: 200mv - 8v 200mv - 8v
Fuse Amp Rating:
40 Amp
80 Amp
Dimensions:
Width: 14
Height: 2 3⁄8” (61mm) 23⁄8” (61mm)
Depth: 9” (229mm) 9” (229mm)
3
⁄4” (375mm) 22 1⁄4” (566mm)
3
Page 4
GT-475
GT-4100
1 32 2 4 65 87
1 32 2 4 65 87
Connections
Connections
u Front RCA Input
v Remote Turn-On (female spade connector supplied)
w Rear RCA Input
x Remote Gain Port (refer to GT-RSL manual for installation instruction)
y Front Left/Right/Mono Speaker Outputs (12-gauge accepted)
z Rear Left/Right/Mono Speaker Outputs (12-gauge accepted)
{ 12v Power Input (4-gauge accepted)
| Ground Wire Input (4-gauge accepted)
Top Panel Removal / Installation
The cover panel is secured with two (2) 3mm screws. Once unscrewed, pull panel forward,
once clear of the corners of the end panels, it will lift off. Reverse to reinstall.
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1
6 7
11
10
43 82 5 9
12
1
6 7
11
10
43 82 5 9
12
GT-475
GT-4100
Controls
Red
Orange
Controls
u Signal Routing Switch (Sends Front RCA Signal to Rear Channels)
v Front Channel Input Sensitivity (250mv to 8.0v - continuously variable)
w Front Channel Highpass Frequency Adjustment (20Hz to 350Hz - variable)
x Front Channel Highpass Crossover OFF/ON Switch
y Front Channel Highpass Crossover Q-Tune
z Rear Channel Stereo / Mono Switch
{ Rear Channel Remote Gain OFF / ON Switch (ON when using GT-RSL)
| Rear Channel Channel Highpass / Lowpass Crossover Selection Switch
} Rear Channel Input Sensitivity (250mv to 8.0v - continuously variable)
~ Rear Channel HP / LP Frequency Adjustment (20Hz to 350Hz - variable)
Rear Channel Crossover OFF/ON Switch
Fuse (replace with same value mini ANL only, refer to specifications on page 3)
Status LEDs
™
Adj. (0.707 to 1.6 - variable)
The Boston Logo will illuminate “Red” under normal operating conditions.
The Orange LED (not visible unless lit) will illuminate during start-up and under fault conditions. If this
is illuminated after start-up, please refer to troubleshooting on page 12.
5
Page 6
Installation - General
WARNING! Before driving the amplifier mounting screws through any surface, be sure of what is behind that
surface. Check for the gas tank, brake lines, and any vehicle wiring harness. Never run wires outside or under
the vehicle or where they could become broken or interfere with the safe operation of the vehicle.
Before You Install
Before you install the unit, disconnect the negative (–) battery cable in the engine compartment of the vehicle.
Doing so will prevent damage to both the electrical system of the vehicle and the amplifier during installation.
Battery and Charging System
In order for the amplifier to function correctly, the electrical system of the vehicle should be professionally
checked for overall electrical capacity. When used, the amplifier will increase the demand on the battery and
alternator. Therefore, both should be thoroughly evaluated before installing the amplifier to ensure they are in
normal operating condition and able to handle the increased demand the amplifier will present to the vehicle’s
electrical system.
Installation - General
Wire Routing
Do not run the power wire near any low-level signals or audio cables such as the RCAs from the head unit.
Noise can be introduced into the amplifier when this occurs. It is helpful to diagram the wire layout first
before any installation is initiated.
Choose the Mounting Location
Plan your installation so that the amplifier is mounted where adequate ventilation is available. Never mount
an amplifier in the engine compartment of a vehicle!
WARNING! Before driving the mounting screws through any surface, be sure of what lies behind that
surface. Check for gas tank, brake lines, and any vehicle wiring harness.
Passenger and Trunk Compartment Mounting
If the amplifier is mounted under a seat, be sure that the vents do not become blocked. Do not allow seat
padding or other obstructive material to press down on the amplifier.
All Boston GT®amplifiers have top panel controls. If the amplifier is mounted under a seat, position the
amplifier so the cover panel can be removed with the seat forward or back to allow adjustment of the audio
settings.
When mounting in a trunk, choose a location that will be protected from sliding cargo or other materials. Mount
the amplifier to solid surfaces only. Do not mount to plastic trim panels. Do not mount the amplifier with Velcro,
double-stick tape, or by wedging into position. Amplifier should be mounted using the movable mounting feet
and the provided mounting screws.
Multi-Position Mounting Feet
The mounting feet are designed to slide in both directions to clear installation obstructions on the mounting
surface.
Venting (Side and Rear)
The cooling vents must be kept clear of obstructions once the amplifier is installed. If the vents are obstructed,
this could lead to premature thermal shutdown or amplifier failure.
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Installation - Wiring
Amplifier Fuses
Although the amplifier has an internal fuse, additional fuse protection should be installed as close as possible
to the battery on the positive (+) power wire going to the amplifier. An inline fuse should be installed at no
more than 18" (46cm) on the positive (+) power wire. The rating of the inline fuse should equal the value of
he internal fuse of the amplifier if only the single amplifier is connected to this wire. If other devices are con-
t
nected to this wire, the fuse value should be of sufficient capacity to handle the demand.
Wire Gauge
The amplifier accepts up to 4-gauge stripped wire at the DC power and ground input terminals, and 4-gauge is
recommended. Wire runs should be kept to the minimum practical length.
Power 12v and Ground (GND) Connection
Strip approximately 5⁄8" (16mm) of insulation. The positive (+) power wire is installed into the amplifier terminal
marked “12v”. The negative (–) wire is installed into the terminal marked “GND”. The ground wire should be
as short as possible and connected directly to the chassis of the vehicle. Make sure that the chassis
connection point is free of rust, grease, dirt, paint, and other materials that may insulate the ground wire from
making proper connection. Tighten the 12v and GND terminals with the supplied 3mm hex wrench to secure
the wire into the terminals. If the power wire must be routed through a drilled or existing hole, use a nylon
panel grommet to prevent the insulation from fraying. Failure to do so could lead to an electrical short if the
wire insulation is worn through and the power wire is shorted to ground.
Installation - Wiring
Remote Input Connection
Use the supplied FEMALE quick-connect terminal to connect the REMOTE trigger lead from the head unit to
the amplifier. Crimp connector to wire from head unit that controls remote turn-on (refer to head unit owner’s
manual). Once the quick-connect terminal is crimped into place, carefully push connector onto recessed MALE
REMOTE terminal adjacent to the RCA input pair (refer to the diagram on page 4).
Speaker Output Connection
Prepare each wire by stripping approximately 5⁄8" (16mm) of insulation. The positive (+) speaker wires are
installed into the amplifier terminals marked “SPEAKER OUTPUT” / “+” (refer to the diagram on page 4). The
negative (–) speaker wires are installed into the amplifier terminals marked “SPEAKER OUTPUT” / “-”. Tighten
the “SPEAKER OUTPUT”, “+”, and “-” terminals with the supplied 2mm hex wrench to secure the wires into
the terminals. If the speaker wires must be routed through a drilled or existing hole, use a nylon panel
grommet to prevent fraying the wire insulation. Failure to do so could lead to an electrical short if the wire
insulation is worn through and the speaker wires are shorted to ground.
Mono Subwoofer Operation
When the amplifier is configured for mono operation, use the speaker output terminals marked for mono use
(refer to the diagram on page 4).
ARNING!
W
Subwoofer impedance must not fall below 2 ohms when in MONO mode.
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Page 8
Tuning The Amplifier - Front and Rear Speakers
1) Music
The material chosen for system tuning must be both clear in recording quality and dynamic in amplitude. Many
audiophile “test” discs have musical tracks with both of these characteristics and should be used.
2) Front Signal Routing Switch
If using two sets of RCAs (independent front and rear RCAs), set the switch to DEDICATED FRONT AND REAR
INPUTS . If you are using one set of RCAs for both front and rear channels, set the switch to SEND FRONT RCA
IGNAL TO REAR. (refer to the diagram on page 5).
S
2) Input Sensitivity Control
Turn both front and rear controls all the way counterclockwise (minimum position). In this position, the amplifier will
be less sensitive to the input signal from the head unit (refer to the diagram on page 5).
3) Highpass & Lowpass Crossover Controls
Crossovers should be turned “OFF” during this phase of setup . Move the HIGHPASS and X-OVER switches to the
“OFF” position (refer to the diagram on page 5), with these settings, full-range signal is sent to the speaker
outputs. Start with the front channels. If over-excursion is detected from speakers, move HIGHPASS switch to “ON”
and slowly rotate clockwise until over-excursion is eliminated. Repeat for the rear channels.
4) Head Unit
The head unit should have all controls such as bass, treble, balance, and fader set to the flat or centered position.
The volume control should be at the minimum setting. If the head unit has any equalization or bass management
features such as boost, they should be defeated at this time. Turn head unit on, and verify that the RED status LED
(logo) is illuminated on the amplifier.
Tuning - Front and Rear Speakers
5) Volume
With the chosen musical track playing, turn the head unit volume control up until the maximum level of
undistorted signal is heard from the speakers. (For most head units, this will be near the end of the volume
control range.)
WARNING! A distorted signal from the head unit sent to the amplifier can cause loudspeaker failure at higher
listening levels.
4-Channel Highpass Operation Switch Configuration Diagram
8
Page 9
fuse
Tuning The Amplifier - Front and Rear Speakers
6) Input Sensitivity Control
Starting with the front channels, slowly rotate the control clockwise (refer to the diagram on page 5) until maximum undistorted playing level is heard from the speakers. Listen closely for bottoming from the speakers. If detected, rotate the input sensitivity control counterclockwise until it is eliminated. Repeat for the rear channels.
7) Crossover Controls
To achieve higher undistorted playing levels from the both the front and rear speakers, the highpass crossover must
e engaged. Starting with the front channels, rotate the crossover control fully clockwise (refer to the diagram on
b
page 5). The highpass crossover point is now set at 350Hz. Rotate “Q-Tune™” Control fully counterclockwise (front
channels only). Move crossover switch to the right (ON) position.
Slowly rotate the input sensitivity control clockwise until maximum undistorted playing level is heard from the
speakers. Listen closely for bottoming from the speakers. If detected, rotate the input sensitivity control counterclockwise until it is eliminated. Slowly rotate the highpass crossover control counterclockwise while listening for
bottoming. You are lowering the crossover point, which means that more bass signal is being sent to the speakers. If
bottoming is detected, rotate the input sensitivity control counterclockwise until it is eliminated and/or rotate the
Highpass crossover control clockwise to raise the crossover point. Repeat for the rear channels.
8) Q-Tune™Control (Front Channels Only)
Once the highpass crossover point has been determined, use the Q-Tune™control (refer to the diagram on page 5)
to increase the bass information centered around the crossover point.
Tuning - Front and Rear Speakers
™
Setting the Q-Tune
crossover frequency controls. You may find while setting the Q-Tune™that over-excursion may be detected in the
front speakers; lowering the Q-Tune
Minor adjustments to each setting are required to fine-tune the system.
Setting the Q-Tune™is a subtle process. It is recommended that the Q-Tune™setting be left in the 0.7 position and
adjusted only after the input sensitivity and highpass crossover ranges are known. Small adjustments to the Q-Tune
setting are all that are required to fine-tune the system.
control is done in conjunction with setting the levels on the input sensitivity and highpass
™
input sensitivity or raising the highpass crossover point will eliminate this.
™
4-Channel Operation Wiring Configuration Diagram
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Page 10
Tuning - Subwoofers
Tuning The Amplifier - Front Speakers and Subwoofer (s)
1) Front Signal Routing Switch
If using two sets of RCAs (independent front and rear RCAs), set the switch to DEDICATED FRONT AND REAR
INPUTS . If you are using one set of RCAs for both front and rear channels, set the switch to SEND FRONT
RCA SIGNAL TO REAR. (refer to the diagram on page 5).
2) Head Unit
The head unit should have all controls such as bass, treble, balance, and fader set to the flat or centered
position. The volume control should be at the minimum setting. If the head unit has any equalization or bass
management features such as boost, they should be deactivated at this time. Turn head unit on, and verify
that the RED status LED (logo) is illuminated on the amplifier.
3) Volume
With the chosen musical track playing, turn the head unit volume control up until the maximum level of
undistorted signal is heard from the speakers. For most head units, this will be at the end of the volume
control range.
WARNING! A distorted signal from the head unit sent to the amplifier can cause speaker failure at higher
listening levels.
4) Input Sensitivity Control (Front and Rear Channels)
Turn control (refer to the diagram on page 5) all the way counterclockwise (minimum position). In this
position, the amplifier will be less sensitive to the input signal from the head unit. Slowly rotate this control
clockwise until maximum undistorted playing level is heard from the subwoofer(s). Listen closely for faults
such as bottoming from the subwoofer(s). If fault is detected, rotate input sensitivity control counterclockwise
until fault is eliminated. At this point, the maximum undistorted subwoofer playing level has been defined.
5) Highpass Crossover Control (Front Channel Only)
To achieve higher undistorted playing levels from the front speakers, the highpass crossover must be
engaged. Rotate the crossover control fully clockwise (refer to the diagram on page 5). The highpass
crossover point is now set at 350Hz. Rotate “Q-Tune™” Control fully counterclockwise. Move crossover
switch to the right (ON) position.
10
Bridged Lowpass with Q-Tune™Switch Configuration Diagram
Page 11
fuse
Tuning The Amplifier - Front Speakers and Subwoofer (s)
Highpass Crossover Control (Front Channel Only) Cont.
Slowly rotate the input sensitivity control clockwise until maximum undistorted playing level is heard from the
speakers. Listen closely for bottoming from the speakers. If detected, rotate the input sensitivity control
ounterclockwise until it is eliminated. Slowly rotate the highpass crossover control counterclockwise while
c
listening for bottoming. You are lowering the crossover point, which means that more bass signal is being
sent to the speakers. If bottoming is detected, rotate the input sensitivity control counterclockwise until it is
eliminated and/or rotate the Highpass crossover control clockwise to raise the crossover point.
6) Q-Tune™ Control (Front Channel Only)
Once the highpass crossover point has been determined, use the Q-Tune™ control (refer to the diagram on
page 5) to increase the bass information centered around the crossover point.
Setting the Q-Tune™ control is done in conjunction with setting the levels on the input sensitivity and highpass crossover frequency controls. You may find while setting the Q-Tune™ that over-excursion may be
detected in the front speakers; lowering the Q-Tune™ input sensitivity or raising the highpass crossover point
will eliminate this. Minor adjustments to each setting are required to fine-tune the system.
Setting the Q-Tune™ is a subtle process. It is recommended that the Q-Tune™ setting be left in the 0.7 position
and adjusted only after the input sensitivity and highpass crossover ranges are known. Small adjustments to
the Q-Tune™ setting are all that are required to fine-tune the system.
Tuning - Subwoofers
7) Rear Input Switch
For dual RCA Input, set switch to STEREO. If one RCA is used, move switch to the right-hand (MONO) position
(refer to the diagram on page 5)
8) Lowpass Crossover Control (Rear Channels Only)
Move the selector switch to “ON” (refer to the diagram on page 5). In this setting, lowpass signal is sent to the
speaker outputs. Experiment with the crossover point settings while the subwoofer is active. A higher setting
will increase the perceived output, and a lower setting will make the bass response more omnidirectional.
9) RSL Control (Rear Channels Only)
The remote level control (GT-RSL) gives you independent level adjustment of the subwoofer’s output level
beyond the standard system volume control. Please refer to the RSL’s manual for installation instruction. The
GT-RSL is available separately, please consult your authorized Boston Acoustics dealer.
3 Channel Operation Wiring Configuration Diagram
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Page 12
Amplifier Troubleshooting Guide
tatus LEDs on Amplifier not Lit—Head Unit (Source) Turned “ON”
S
Verify Remote turn-on wire from source to amplifier has proper voltage
Status LEDs Lit, no Output from Speakers—Speakers in Normal Operating Condition
Verify High-level cables from speaker(s) to amplifier are securely connected
Power (B+) connections at amplifier, terminal blocks, and battery are secure
Ground (GND) connections at amplifier and vehicle chassis are secure
Battery B+ fuse and amplifier fuse are OK
B+ at battery and B+ at amplifier have proper voltage
RCA cables from amplifier to source are securely connected
Sensitivity adjustment on amplifier is correctly adjusted
Engine Noise from Speaker(s)
Verify RCA cables are of good quality with no breakage to internal shields
Amplifier Output Distorted—Music not Recorded with Intentional Distortion
Verify Source output to amplifier is not distorted
Amplifier Shutting Down, Red Blinking and Orange LEDs Lit—Amplifier in Thermal Protection Mode
Verify Amplifier is mounted with adequate air circulation around vents
Amplifier not Turning “ON”, Orange LED Lit—Amplifier not Connected to a Shorted Speaker
Verify Speaker crossover is not defective
Amplifier not Turning And Both LED (s) Blinking—Speakers, Crossovers, and Cable OK
Verify Replace fuse with fuse of same value
Amplifier not Turning “ON”, Orange LED Lit—Speakers, Crossovers, and Cable OK
Turn source “OFF” and disconnect RCA cables at amplifier
If noise stops, check equipment and cables leading to amplifier
RCA cables from source to amplifier are not run alongside power
Amplifier input sensitivity is correctly adjusted
Amplifier does not have obstructions blocking back or side panel vents
Amplifier is not mounted under carpet
Speakers meet correct impedance for application (mono or stereo hookup)
High-level cables from speaker to amplifier are not shorted
Internal fuse needs to be replaced
Amplifier requires service
If Service Seems Necessary
First, contact the dealer from whom you purchased the product, or contact us via e-mail at:
USA and Canada: suppor
t@bostona.com
Europe: support@bostona.com
Japan: ba_info@dm-holdings.com
Asia/Pacific countries: ser
vice@dm-singapore.com
We will promptly advise you of what action to take.
Boston Acoustics, Inc. 300 Jubilee Drive, Peabody, MA 01960 USA
: bostonacoustics.com
Boston, Boston GT
Specifications ar
: 978.538.5000 F: 978.538.5100 W
T
, Boston Acoustics, and the Boston Acoustics logo are registered trademarks and DualMode and Q-Tune are trademarks of Boston Acoustics, Inc.
e subject to change without notice. © 2008 Boston Acoustics, Inc. All rights reserved. Covered by patents issued and/or pending. 142-003179-1
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