Boston Acoustics GT 42 User Manual

GT-42  
4-Channel, High-Current/High-Power Amplifier  
Parts List  
Included Hardware  
(1) owners manual  
(1) female quick-connect terminal for remote input  
(1) 2mm hex wrench (for speaker input)  
(1) 3mm hex wrench (for power input)  
(6) mounting screws  
Features and Specifications  
GT-42 Features  
4-Channel, High-Current Amplifier  
Continuously Variable Crossover and Q-factor Settings  
2Bridge Stable (Mono) Operation  
Selectable Highpass Front Channels  
Power Increase with Input Voltage Rise  
Advanced Cooling Allows Varied Mounting Positions  
Adjustable Feet for Varied Mounting Surfaces  
Security Cover Protects Control Settings  
24dB or 12dB Octave Lowpass Setting  
Selectable Mono/Stereo Rear or Subwoofer Lowpass  
Selectable Rear Channel Signal Derived from Front Channel Input  
Optional Remote Subwoofer Control  
Enhanced Switching Assignments  
GT-42Specifications  
14.4VDC Power  
@ 4 Ohms  
4x100W  
4x150W  
2x300W  
2x450W  
@ 2 Ohms  
@ 4 Ohms (mono)  
@ 2 Ohms (mono)  
12.6VDC Power  
@ 4 Ohms  
4x75W  
@ 2 Ohms  
4x120W  
2x250W  
2x350W  
@ 4 Ohms (mono)  
@ 2 Ohms (mono)  
14.4VDC Multi-channel Power  
12.6VDC Multi-channel Power  
Frequency Response (-3dB)  
Signal-to-Noise Ratio (A Weighted)  
Dimensions  
2x100W (4 ohm), 1x450W (2 ohm)  
2x75W (4 ohm), 1x350W (2 ohm)  
10Hz–95kHz  
>100dB  
21/4x215/8x87/8” (57 x 548 x 225mm)  
3
Control Functions  
3
5
9
12  
10  
STEREO  
SEND  
INPUT  
REAR  
OFF  
200  
ON  
STEREO  
MONO  
L
OFF  
ON  
OFF  
ON  
FUSE  
3
x
25A  
FRONT INPUT  
HIGHPASS  
REAR INPUT  
SUBWOOFER LEVEL  
LOWPASS SLOPE  
12dB 12dB 24dB  
ST  
MONO  
LOWPASS  
350  
350  
Hz  
20  
200  
Hz  
50  
6
MONO  
MONO  
B+  
B+  
GND  
GND  
0.2  
1.2  
0.2  
V
L
R
L
R
INPUT SENSITIVITY 2.6  
REMOTE  
0.95  
Q/HP  
0.7  
INPUT SENSITIVITY 2.6  
V
5
5
REMOTE  
SUBWOOFER LEVEL  
FRONT SPEAKER OUTPUT  
REAR SPEAKER OUTPUT  
12.6–14.4VDC  
GROUND  
N O N P R I N TA B L E A R E A  
4
4
11  
1
7
MONO  
MONO  
12.6–14.4VDC  
GROUND  
STATUS  
2
FRONT SPEAKER OUTPUT  
REAR SPEAKER OUTPUT  
B+  
B+  
GND  
GND  
L
R
L
R
12  
ON  
SAFE  
8
1
FRONT RCA Inputs  
RCA cables marked “FRONT” from head unit or from other line level device  
should be connected here. Use both inputs (L & R) for stereo.  
1
2
2
FRONT Remote Input  
Use the supplied FEMALE quick connector to connect the REMOTE trigger lead  
from the head unit to the amplifier. Amplifier turns “ON” when head unit is turned  
“ON.” One FEMALE .210" connector is supplied with amplifier.  
3
FRONT Input Switch  
In the left position, the L & R inputs go to the FRONT L & R channels of the ampli-  
fier. In the right position, the L & R inputs go to the FRONT and REAR L & R chan-  
nels of the amplifier.  
4
FRONT and REAR Sensitivity  
Turn control clockwise to increase the amplifier sensitivity to incoming signals. Turn  
control counterclockwise to decrease the amplifier sensitivity.  
5
FRONT Highpass Crossover Controls  
To use 12dB/octave crossover, move switch to right-hand position. Highpass  
crossover frequency is adjustable from 20Hz to 350Hz by rotary control. (Moving  
switch to left-hand position will bypass crossover functions.)  
4
Control Functions (cont.)  
“Q” Control  
6
“Q” Control is active when the highpass crossover is engaged and is centered  
on the selected crossover point. The range of operation is 0.7–1.2.  
dB  
Q
+1.6dB  
0dB  
-3dB  
.707 .95 1.2  
t(tuned crossover frequency)  
7
REAR RCA Inputs  
RCA cables marked “REAR” from head unit or other line level device should be  
connected here. Use both inputs (L & R) for stereo.  
7
8
8
REAR Remote Input  
This remote input is parallel to the FRONT remote input and does not need to  
be connected for the amplifier to operate. Use either remote input to turn the  
amplifier on. Do not connect 12V accessories to this input.  
9
REAR Input Switch  
In the left position, the L & R inputs go to the REAR L & R channels of the ampli-  
fier. In the right (MONO) position, the inputs are summed. Use this setting when  
the REAR channels are used with a subwoofer.  
10  
Lowpass Slope and Crossover Controls  
OFF  
200  
ON  
Select appropriate crossover slope of 12 or 24dB/octave by  
LOWPASS  
moving LOWPASS SLOPE switch. Lowpass crossover fre-  
quencies are adjustable from 50Hz to 350Hz by rotary control.  
Move filter switch to “ON” position to engage.  
LOWPASS SLOPE  
350  
12dB 12dB 24dB  
Hz  
50  
ST  
MONO  
11  
Status LED Indicators  
GREEN indicates the normal operating condition; the amplifier is “ON.” GREEN  
and RED together are normal when the amplifier is first turned “ON”; RED will  
turn off after a few seconds. When both GREEN and RED remain on, the ampli-  
fier is in thermal shutdown condition. RED only indicates a fault condition, “SAFE.”  
5
Control Functions (cont.)  
12  
Subwoofer Level Control and Port  
Switch should be set to “OFF” when control circuit is not installed,  
(see optional “subwoofer level control” owners manual).  
cover panel  
Mechanical Functions  
Recessed RCA Inputs  
The input jacks are recessed into the body of the amplifier to provide clear-  
ance in tight mounting locations.  
1 inch  
1 inch  
Control Cover Removal and Reinstallation  
The cover panel is secured with two (2) captive coin-slotted screws. Coin-slotted  
screws allow a coin edge to be used as a screwdriver to remove the panel.  
Multi-position Mounting Feet  
The mounting feet are designed to slide in both directions to clear installation  
obstructions on the mounting surface.  
WARNING! Before driving the mounting screws through any surface, be sure  
of what is behind that surface. Check for the gas tank, brake lines, and any vehi-  
cle wiring harness.  
Vents (Side and Rear)  
The cooling vents must be kept clear of obstructions once the amplifier is installed. Failure to do this could  
lead to premature thermal shutdown or amplifier failure.  
upper side vent  
lower side vent  
6
Mechanical Functions (cont.)  
Amplifier Linking  
The design of the side panels enables multiple amplifiers to be used together without additional hardware.  
GT-42  
GT-20  
Wire Connection  
Amplifier accepts stripped wire directly into the terminal blocks. Speaker outputs accept 8-gauge, and the  
DC power and ground accept 4-gauge. Tighten with supplied hex wrenches.  
Fuses  
Amplifier accepts standard AT-style automotive blade fuses.  
FUSE  
3
x
20A  
7
General Installation Precautions  
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 vehi-  
cle. 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 professional-  
ly 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 vehicles electrical system.  
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 attempted.  
8
Installation—Amplifier Mounting  
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 is behind that sur-  
face. Check for gas tank, brake lines, and any vehicle wiring harness.  
13mm (1/2”)  
7
225mm (8 /8”)  
GT-42  
STATUS  
MONO  
MONO  
12.6–14.4VDC  
GROUND  
FRONT SPEAKER OUTPUT  
REAR SPEAKER OUTPUT  
1
B+  
B+  
GND  
GND  
L
R
L
R
57mm (2 /4”)  
ON  
SAFE  
5
548mm (21 /8”)  
9
Installation—Amplifier Mounting (cont.)  
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 slid-  
ing 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.  
Installation—Fuses and Wiring  
Amplifier Fuses  
Although the amplifier has internal fuses, additional fusing should be pro-  
vided at 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 pos-  
itive (+) power wire. The rating of the inline fuse should equal the value of  
the internal fuses of the amplifier if only the amplifier is connected to this  
wire. If other devices are connected to this wire, the fuse value should be  
of sufficient capacity to handle the demand.  
FUSE  
3
x
20A  
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.  
10  
Installation—Fuses and Wiring (cont.)  
Power/B+ and Power/GND Connection  
Strip approximately 5/8" (16mm) of insulation. The positive (+) power wire  
is installed into the amplifier terminal marked “B+.” 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 B+ 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 grom-  
met 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 power wire  
is shorted to ground.  
Strip 5/8" (16mm)  
Remote Input Connection  
Use the supplied FEMALE slide connector to connect the REMOTE trig-  
ger lead from the head unit to the amplifier. Crimp connector to wire from  
head unit that controls remote turn-on (refer to head unit owners manu-  
al). Once the slide connector is crimped into place, carefully push connector  
onto recessed male REMOTE terminal adjacent to the RCA Input pair. Only  
one (1) remote turn-on terminal should be connected.  
Speaker Output Connection  
Prepare each wire by stripping approximately 5/8" (16mm) of insulation. The positive (+) speaker wire is  
installed into the amplifier terminal marked “SPEAKER OUTPUT” / “+.” The negative (–) speaker wire is  
installed into the amplifier terminal marked “SPEAKER OUTPUT” / “-.” Tighten the “Speaker Output”, “+”,  
and “-” terminals with the supplied 2mm hex wrench to secure the wire 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.  
11  
Installation—Fuses and Wiring (cont.)  
Mono Subwoofer Operation  
If the amplifier is to be bridged and used with a subwoofer connected to the REAR channels, use the  
“SPEAKER OUTPUT” terminals marked for mono use.  
WARNING! Subwoofer impedance must not fall below 2 ohms when in MONO mode.  
2-ohm minimum  
Setup Tuning—Full-Range Speakers  
1) Music  
The material chosen for head unit/amplifier system setup must be both clear in recording quality and dynam-  
ic in amplitude. Many audiophile “test” discs have musical tracks with both of these characteristics and should  
be used.  
2) FRONT and REAR Sensitivity Controls  
Turn controls all the way counterclockwise (minimum position). In this position,  
the amplifier will be less sensitive to the input signal from the head unit.  
3) FRONT and REAR Crossover Controls  
Crossovers should be turned off during this phase of set-up. Move the HIGHPASS and FILTER switches to  
the “OFF” position—with these settings, full-range signal is sent to the FRONT & REAR speaker outputs.  
OFF  
200  
ON  
OFF  
185  
ON  
LOWPASS SLOPE  
12dB 12dB 24dB  
LOWPASS  
350  
HIGHPASS  
350  
ST  
MONO  
Hz  
50  
Hz  
20  
FRONT crossover control  
REAR crossover control  
12  
Setup Tuning—Full-Range Speakers (cont.)  
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 GREEN status LED is lit on the amplifier.  
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 high-  
er listening levels!  
6) FRONT Input Sensitivity Control  
Slowly rotate control clockwise until maximum undistorted playing level is  
heard from the speakers. Listen closely for bottoming from the speakers. If  
detected, rotate FRONT Input Sensitivity counterclockwise until it is eliminated.  
7) FRONT Crossover Controls  
To achieve higher undistorted playing levels from the front speakers, the  
FRONT crossover must be engaged. Rotate crossover control fully clockwise.  
The highpass crossover point is now set at 350Hz. Rotate FRONT “Q” Control  
fully counterclockwise. Move crossover switch to the right (ON) position.  
OFF  
185  
ON  
HIGHPASS  
350  
Slowly rotate FRONT input sensitivity control clockwise until maximum undis-  
torted playing level is heard from the speakers. Listen closely for bottoming  
from the speakers. If detected, rotate FRONT input sensitivity control coun-  
terclockwise until it is eliminated. Slowly rotate FRONT highpass crossover con-  
Hz  
20  
trol 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 FRONT input sensitivity  
control counterclockwise until it is eliminated and/or rotate the FRONT highpass crossover control clock-  
wise to raise the crossover point.  
13  
Setup Tuning—Full-Range Speakers (cont.)  
8) FRONT “Q” Control  
Once the FRONT highpass crossover point has been determined, use the  
FRONT “Q” control to increase the bass information centered around the  
crossover point.  
Setting the front “Q” 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” that bottoming may be detected in the front speakers;  
lowering the “Q” 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” is a subtle process. It is recommended that the “Q” 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” setting are all that are required to fine-tune the system.  
9) REAR Input Sensitivity and Crossover Controls  
OFF  
200  
ON  
Setting levels for the rear channels proceeds the same as for  
the front except for the elimination of the “Q” control settings.  
Crossover selector switch must be set to “HP” and filter switch  
must be set to “ON.” If the loudspeaker being used is capa-  
ble of full-range operation, filter should be set to “OFF.”  
LOWPASS SLOPE  
12dB 12dB 24dB  
LOWPASS  
350  
ST  
MONO  
Hz  
50  
Setup Tuning—Rear Fill Speakers  
You may set the rear channels for summed mono operation from the L & R REAR RCA inputs by setting the  
REAR INPUT switch to the right-hand MONO position and then connecting the L & R REAR loudspeakers  
normally as you would for regular stereo operation. This configuration is beneficial for rear fill in some appli-  
cations.  
Setup Tuning—Subwoofers  
1) SUBWOOFER LEVEL Control  
Refer to subwoofer level control in owners manual. If the control is not used, SUBWOOFER LEVEL switch  
must be set to “OFF.”  
2) REAR Input Switch  
Move switch to the right-hand (MONO) position, the inputs are summed to mono. Connect the subwoofer  
to the REAR SPEAKER OUTPUT terminals marked for MONO operation. NOTE: Subwoofer impedance is  
2 ohms minimum.  
14  
Setup Tuning—Subwoofers (cont.)  
3) 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 GREEN status LED is lit on the amplifier.  
4) 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 loudspeaker failure at  
higher listening levels!  
5) REAR Input Sensitivity Control  
Turn controls all the way counterclockwise (minimum position). In this position, the amplifier will be less sen-  
sitive to the input signal from the head unit. Slowly rotate this control clockwise until maximum undistorted  
playing level is heard from the subwoofers. Listen closely for faults such as bottoming from the subwoofer.  
If fault is detected, rotate REAR input sensitivity control counterclockwise until fault is eliminated. At this  
point, the maximum undistorted subwoofer playing level has been defined.  
6) REAR Crossover Control  
Move the selector switch to “LP” and the FILTER switch to “ON.” In this setting, lowpass signal is sent to  
the REAR speaker outputs. Select 12 or 24dB/octave.  
7) PHASE  
Subwoofer phase is relative to the front loudspeakers. Correct electrical phase does not always mean  
correct acoustic phase. Swap positive (+) and negative (-) connections at the speaker outputs where the  
subwoofer is connected to the amplifier. It is beneficial to listen to the subwoofer connected in both phase  
conditions. The subwoofer should be left in the condition in which the strongest bass response is noted.  
15  
System Examples  
System A—Full-Range Front with Full-Range Rear  
to ground  
to ground  
fuse  
fuse  
to + battery terminal  
to + battery terminal  
System B—Full-Range Front with Rear Fill  
to ground  
to ground  
fuse  
to + battery terminal  
to + battery terminal  
fuse  
16  
System Examples (cont.)  
System C—Main Speakers with Single Subwoofer (2)  
to ground  
to ground  
fuse  
fuse  
to + battery terminal  
to + battery terminal  
2  
10.5LF  
System D —Main Speakers with Parallel 4Subwoofers (2load)  
to ground  
to ground  
fuse  
fuse  
to + battery terminal  
to + battery terminal  
6.5LF  
6.5LF  
17  
Amplifier Troubleshooting Guide  
Status LEDs on Amplifier not LitHead Unit (Source) Turned “ON”  
Verify  
Remote turn-on wire from source to amplifier has proper voltage  
Power (B+) connections at amplifier, terminal blocks, and battery are secure  
Ground (GND) connections at amplifier and vehicle chassis are secure  
Battery B+ fuse is OK  
Amplifier fuse is OK  
B+ at battery and B+ at amplifier have proper voltage  
Status LEDs Lit, no Output from SpeakersSpeakers in Normal Operating  
Condition  
Verify  
High-level cables from speaker(s) to amplifier are securely connected  
RCA cables from amplifier to source are securely connected  
Sensitivity adjustment on amplifier is correctly adjusted  
Engine Noise from Speaker(s)  
Turn source “OFF”  
Disconnect RCA cables at amplifier  
If noise stops, check equipment & cables leading to amplifier  
Verify  
RCA cables are of good quality with no breakage to internal shields  
RCA cables from source to amplifier are not run alongside power  
Amplifier Output DistortedMusic not Recorded with Intentional Distortion  
Verify  
Source output to amplifier is not distorted  
Amplifier input sensitivity is correctly adjusted  
Amplifier Shuts Down, Red and Green LEDs are LitAmplifier is in Thermal  
Protection Mode  
Verify  
Amplifier is mounted with adequate air circulation around vents  
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)  
Amplifier Does Not Turn “ON”, and Red LED is LitAmplifier not Connected to  
a Shorted Speaker  
Verify  
Speaker crossover is not defective  
High-level cables from speaker to amplifier are not shorted  
Amplifier Does Not Turn “ON”, and Red LED LitSpeakers, Crossovers, and  
Cable are OK  
Amplifier requires service  
18  
Contact and Warranty Information  
Limited Warranty (US)  
For one (1) year from the date of purchase, Boston Acoustics will repair for the original owner any defect in materials  
or workmanship that occurs in normal use, without charge for parts and labor—when purchased from an authorized  
Boston Acoustics retailer.  
If an authorized Boston Acoustics retailer installs your amplifier, the warranty will be extended one (1) additional year.  
Installation of the amplifier must be noted on the original purchase receipt. The receipt must be presented at the time  
a warranty claim is made.  
Your responsibilities are to use the system according to the instructions supplied, to provide safe and secure  
transportation to an authorized Boston Acoustics service representative, and to present proof of purchase in the form  
of your sales slip when requesting service.  
Excluded from this warranty is damage that results from abuse, misuse, accidents, shipping, or repairs or modifications  
by anyone other than an authorized Boston Acoustics service representative.  
This warranty is void if the serial number has been removed or defaced.  
This warranty gives you specific legal rights, and you may also have other rights that vary from state to state.  
If Service Seems Necessary  
First, contact the dealer from whom you purchased the amplifier. If that is not possible, write to:  
Boston Acoustics, Inc. 300 Jubilee Drive Peabody, MA 01960 U.S.A., or your authorized Boston  
Acoustics distributor  
We will promptly advise you of what action to take. If it is necessary to return your unit to the factory, please ship it pre-  
paid. After it has been repaired, we will return it freight prepaid in the U.S.A. and Canada.  
Boston, Boston Acoustics, and the Boston logo are  
registered trademarks of Boston Acoustics, Inc.  
© 2003 Boston Acoustics, Inc. All rights reserved.  
Specifications subject to change without notice.  
P/N 042-001630-1  
300 Jubilee Drive  
Peabody, MA 01960 U.S.A.  
(978) 538-5000  
19  

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