Boston Acoustics GT-28, GT-24 User Manual

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GT-28GT-24

2-Channel,High-Current/High-PowerAmplifiers

Table of Contents

Parts List

3

Features and Specifications

3

Control Functions

4

Control functions (cont.)

5

Mechanical Functions

6

Recessed RCA inputs

6

Control cover removal and reinstallation

6

Multi-positionmounting feet

6

Vents (side and rear)

6

Mechanical functions (cont.)

7

Amplifier linking

7

Wire connection

7

Fuses

7

General Installation Precautions

8

Before you install

8

Battery and charging system

8

Wire routing

8

Installation—AmplifierMounting

9

Choose the mounting location

9

Height, width, and depth diagrams

9

Installation—amplifiermounting (cont.)

10

Passenger & trunk compartment mounting

10

Installation—Fusesand Wiring

10

Amplifier fuses

10

Wire gauge

10

Installation—fusesand wiring (cont.)

11

Power/B+ and power/ground (GND) connection

11

Remote input connection

11

Speaker output connection

11

Installation—fusesand wiring (cont.)

12

Mono subwoofer operation

12

Setup Tuning—Full-RangeSpeakers

12

Music

12

Sensitivity controls

12

Highpass and lowpass crossover controls

12

Setup tuning—full-rangespeakers (cont.)

13

Head unit

13

Volume

13

Input sensitivity control

13

Crossover controls

13

Setup tuning—full-rangespeakers (cont.)

14

“Q” control

14

Setup Tuning—RearFill Speakers

14

Setup Tuning—Subwoofers

14

Input switch

14

Setup tuning—subwoofers(cont.)

15

Head unit

15

Volume

15

Input sensitivity control

15

Lowpass crossover control

15

Phase

15

System Examples

16,17

Amplifier Troubleshooting Guide

18

Contact and Warranty Information

19

2

Parts List

Included Hardware: GT-28&GT-24

(1) owner’s manual

(1) female quick-connectterminal for remote input

(1) 2mm hex wrench (for speaker input)

(1) 3mm hex wrench (for power input)

(6) mounting screws

Features and Specifications

GT-28andGT-24Features

2-Channel,High-CurrentAmplifier

2Ω Mono Operation

Power Increase with Input Voltage Rise

Advanced Cooling Allows Varied Mounting Positions

Adjustable Feet for Varied Mounting Surfaces

24dB or 12dB Octave Lowpass Setting

Continuously Variable Crossover and Q-factorSettings

Selectable Highpass, Lowpass, and Bandpass Settings

Bandpass Configurable for Midbass or Subwoofer

Terminals Accept Bare, Heavy-GaugeWire

Screw-DownSecurity Cover Protects Tuning Controls

Optional Remote Subwoofer Level Control

Technical Specifications

 

 

 

GT-28

GT-24

14.4VDC Power

 

 

@ 4 Ohms

2x250W

2x175W

@ 2 Ohms

2x450W

2x275W

@ 4 Ohms (mono)

1x900W

1x550W

@ 2 Ohms (mono)

1x1350W

1x900W

 

 

 

12.6VDC Power

 

 

@ 4 Ohms

2x200W

2x120W

@ 2 Ohms

2x350W

2x200W

@ 4 Ohms (mono)

1x700W

1x440W

@ 2 Ohms (mono)

1x1100W

1x750W

 

 

 

Frequency Response (-3dB)

10Hz–95kHz

10Hz–95kHz

Signal-to-NoiseRatio (A Weighted)

>100dB

>100dB

Dimensions (HxWxD)

21/4x215/8x87/8” (57x548x225mm)

21/4x18x87/8” (57x458x225mm)

3

Control Functions

3

 

 

9

 

7

 

6

 

5

 

 

 

 

 

 

STEREO

MONO

OFF

ON

 

 

OFF

ON

OFF

ON

 

 

 

 

FUSE 4 x 25A

INPUT

L

SUBWOOFER LEVEL

LOWPASS SLOPE

 

LOWPASS

 

HIGHPASS

 

 

 

 

 

 

 

 

 

 

12dB

12dB 24dB

 

350

 

350

 

 

 

 

 

 

 

 

 

 

ST

MONO

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

200

Hz

185

Hz

 

 

 

 

 

 

 

 

 

 

 

 

 

50

 

20

 

MONO

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0.2

 

1.2

L

R

B+

B+

GND

GND

 

 

 

 

INPUT SENSITIVITY

2.6

 

0.95

Q/HP

 

 

 

 

 

 

I NPUT

REMOTE

SUBWOOFER LEVEL

 

 

 

5

 

0.7

SPEAKER OUTPUT

 

 

 

 

 

 

 

 

 

 

12.6–14.4VDC

GROUND

 

 

 

 

 

4

 

 

8

 

 

 

 

 

 

 

 

 

 

 

 

 

GT-28Top Panel Shown

1

 

 

 

 

 

 

 

STATUS

MONO

12.6–14.4VDC

GROUND

 

 

9

 

 

B+

B+

GND

GND

 

L

R

 

 

 

ON

10

 

 

 

 

 

SAFE

 

 

 

 

2

 

 

 

 

 

 

GT-28Front Panel Shown

1 RCA Inputs

1

RCA cables from head unit or from other line level device should be connected

 

here. Use both inputs (L and R) for stereo; use “L” input for mono.

2

2 Remote Input

Use the supplied FEMALE quick-connectorto 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 Input Switch

STEREO MONO

INPUT L

In the left position, the L and R inputs go to the L and R channels of the amplifier. In the right position, the input is for mono operation.

4 Input Sensitivity Control

Turn control clockwise to increase the amplifier sensitivity to incoming signals. Turn control counterclockwise to decrease the amplifier sensitivity.

5 Highpass Crossover Controls

To use 12dB/octave crossover, move HIGHPASS switch to right-handposition. Highpass crossover frequency is adjustable from 20Hz to 350Hz by rotary control. (Moving switch toleft-handposition will bypass crossover functions.)

0.2

INPUT SENSITIVITY 2.6

5

OFF ON

HIGHPASS

350

185

Hz

20

4

Control Functions (cont.)

6 Lowpass Crossover Controls

To use lowpass crossover move LOWPASS switch to righthand position. Lowpass crossover frequency is adjustable from 50Hz to 350Hz by rotary control. (Moving switch to left-handposition will bypass crossover functions.)

7 Lowpass Slope

Select appropriate crossover slope of 12 or 24dB/octave by moving LOWPASS SLOPE switch.

8 “Q” Control

The “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)

9 Subwoofer Level Control Port

SUBWOOFER LEVEL switch should be set to “OFF” when control circuit is not installed, (see optional Subwoofer Level Control owners manual).

10 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.”

OFF ON

LOWPASS

350

200

Hz

50

LOWPASS SLOPE

12dB 12dB 24dB ST MONO

5

Mechanical Functions

Recessed RCA Inputs

The input jacks are recessed into the body of the amplifier to provide clearance in tight mounting locations.

1 inch1 inch

Control Cover Removal and Reinstallation

The cover panel is secured with two (2) captive coin-slottedscrews.Coin-slot-ted screws allow a coin edge to be used as a screwdriver to remove the panel.

Multi-PositionMounting 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 vehicle 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.

Wire Connection

Amplifier accepts stripped wire directly into the terminal blocks. Speaker outputs accept 8-gauge,and the DC power and ground accept4-gauge.Tighten with supplied hex wrenches.

Fuses

Amplifier accepts standard AT-styleautomotive blade fuses.

FUSE 4 x 25A

FUSE 3 x 20A

GT-28

GT-24

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 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.

Wire Routing

Do not run the power wire near any low-levelsignals 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—AmplifierMounting

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 surface. Check for gas tank, brake lines, and any vehicle wiring harness.

GT-28

GT-24

13mm (1/2")

225mm (87/8")

GT-28 (GT-24depth dimensions are the same)

57mm (21/2")

57mm (21/2")

458mm (18")

548mm (215/8")

9

Installation—AmplifierMounting (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 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, doublestick tape, or by wedging into position. Amplifier should be mounted using the movable mounting feet and the provided mounting screws.

Installation—Fusesand Wiring

Amplifier Fuses

Although the amplifier has internal fuses, additional fusing should be provided 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 positive (+) 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 4 x 25A

GT-28

FUSE 3 x 20A

GT-24

Wire Gauge

The amplifier accepts up to 4-gaugestripped wire at the DC power and ground input terminals, and4-gaugeis recommended. Wire runs should be kept to the minimum practical length.

10

Installation—Fusesand 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 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 power wire is shorted to ground.

1/4"

Strip 5/8" (16mm)

Remote Input Connection

Use the supplied FEMALE quick-connectorto connect the REMOTE trigger lead from the head unit to the amplifier. Crimp connector to wire from head unit that controls remoteturn-on(refer to head unit owner’s manual). Once thequick-connectoris crimped into place, carefully push connector onto recessed MALE REMOTE terminal adjacent to the RCA input pair. Only one (1) remoteturn-onterminal should be connected.

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” / “+”. 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

L

R

SPEAKER OUTPUT

11

Installation—Fusesand Wiring (cont.)

Mono Subwoofer Operation

When the amplifier is configured for mono operation, use the speaker output terminals marked for mono use.

WARNING! Subwoofer impedance must not fall below 2 ohms when in MONO mode.

2-ohmminimum

 

MONO

L

R

SPEAKER OUTPUT

Setup Tuning—Full-rangeSpeakers

1) Music

The material chosen for head unit/amplifier system setup 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) Input Sensitivity Control

 

 

Turn control all the way counterclockwise (minimum position). In this position,

 

0.2

the amplifier will be less sensitive to the input signal from the head unit.

INPUT SENSITIVITY

2.6

 

 

5

3) Highpass & Lowpass Crossover Controls

Crossovers should be turned “OFF” during this phase of setup. Move the HIGHPASS and LOWPASS switches to the “OFF” position—withthese settings,full-rangesignal is sent to the speaker outputs. If bottoming is detected from speakers, move HIGHPASS switch to “ON” and slowly rotate clockwise until bottoming is eliminated.

OFF

ON

OFF

ON

 

 

 

 

 

 

 

HIGHPASS

 

LOWPASS

LOWPASS SLOPE

 

350

 

350

 

 

 

 

185

Hz

200

Hz

12dB 12dB 24dB

ST

MONO

 

 

 

 

 

20

 

50

 

 

Highpass Crossover Control Lowpass Crossover Control Lowpass Slope Control

12

Setup Tuning—Full-RangeSpeakers (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 higher listening levels!

6) Input Sensitivity Control

Slowly rotate control clockwise until maximum undistorted playing level is

0.2

heard from the speakers. Listen closely for bottoming from the speakers. If

INPUT SENSITIVITY 2.6

detected, rotate INPUT SENSITIVITY control counterclockwise until it is elim-

5

inated.

 

7) Crossover Controls

To achieve higher undistorted playing levels from the main speakers, the highpass crossover must be engaged. Rotate crossover control fully clockwise. The highpass crossover point is now set at 350Hz. Rotate “Q” Control fully counterclockwise. 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.

OFF ON

HIGHPASS

350

185

Hz

20

13

Setup Tuning—Full-RangeSpeakers (cont.)

8) “Q” Control

Once the highpass crossover point has been determined, use the “Q” control to increase the bass information centered around the crossover point.

Setting the “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-tunethe 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-tunethe system.

Setup Tuning—RearFill Speakers

You may set the channels for summed mono operation from the L and R RCA inputs by setting the INPUT switch to the right-hand,MONO, position and then connecting the L and R REAR loudspeakers normally as you would for regular stereo operation. This configuration is beneficial for rear fill in some applications.

Setup Tuning—Subwoofers

1) Input Switch

Move switch to the right-hand(MONO) position; the inputs are summed to mono. Connect the subwoofer to the SPEAKER OUTPUT terminals marked for MONO operation. NOTE: Subwoofer impedance is 2 ohms minimum.

14

Setup Tuning—Subwoofers(cont.)

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 GREEN status LED is lit 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 loudspeaker failure at higher listening levels!

4) Input Sensitivity Control

Turn control 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) Lowpass Crossover Control

Move the selector switch to “ON.” In this setting, lowpass signal is sent to the speaker outputs. Experiment with the crossover point setings while the subwoofer is active. A higher setting will increase the perceived output, and a lower setting will make the bass response more omnidirectional. 12 or 24dB crossover slopes are available. Depending on your installation and listening preferences, one will work more effectively.

LOWPASS SLOPE

12dB 12dB 24dB ST MONO

6) 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-RangeFront Speakers

to ground

to ground

fuse

to + battery terminal

fuse

to + battery terminal

5.6 FL

System B—RearFill Speakers

to ground

to ground

fuse

to + battery terminal

fuse

to + battery terminal

5L.6 F

16

System Examples (cont.)

System C—Parallel4Subwoofers (2load)

to ground

to ground

fuse

to + battery terminal

fuse

to + battery terminal

4

10.5LF

4

10.5LF

System D —Series/Parallel2

load)

mono

to ground

to ground

fuse

to + battery terminal

fuse

to + battery terminal

2Ω

2Ω

2Ω

2Ω

10.5LF

10.5LF

10.5LF

10.5LF

17

Amplifier Troubleshooting Guide

Status LEDs on Amplifier not LitHeadUnit (Source) Turned “ON”

Verify

Remote turn-onwire 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 SpeakersSpeakersin Normal Operating Condition

Verify

High-levelcables 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 and 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 DistortedMusicnot Recorded with Intentional Distortion

Verify

Source output to amplifier is not distorted

 

Amplifier input sensitivity is correctly adjusted

Amplifier Shutting Down, Red and Green LEDs LitAmplifierin 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 not Turning “ON”, Red LED LitAmplifiernot Connected to a Shorted Speaker

Verify

Speaker crossover is not defective

 

High-levelcables from speaker to amplifier are not shorted

Amplifier not Turning “ON”, Red LED LitSpeakers,Crossovers, and Cable 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—whenpurchased 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 prepaid. After it has been repaired, we will return it freight prepaid in the U.S.A. and Canada.

www.bostonacoustics.com

300 Jubilee Drive Peabody, MA 01960 U.S.A.

(978) 538-5000

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 042-1801-0

19