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8

3-Channel Bi-Amplified

4-Channel Input (Fading Subwoofer)

GR 1

GR 3

GR 2

2-Channel Input (Mono Subwoofer)

4-Channel Full-Range or Bi-Amplified

Preamp or

Speaker-Level

Input

GR 1

GR 2

GR 1

GR 2

GR 3

GR 3

GR 1

GR 2

GR 3

Front Speakers

Use these when
4-channel output
is available.

Main Speakers

Note: Image Enhancement cannot be used in these applications.

Subwoofer

Rear Speakers

or Subwoofer

4-Channel Bi-Amplified with 
Fading Mono Subwoofers

4-Channel Full-Range

*Stereo subwoofers may also be used by selecting “ST”
on the group 3 input mode switch.

Note: Image Enhancement cannot be used in these applications.

GTH400-20107  06/03/98 15:49  Side 8

9

1. Preamp-Level Input Connector –

Use these connectors for line (pre-
amp) level inputs to the amplifier.

2. Preamp-Level Output Connector –

Use these outputs to send 
signal to additional amplifiers.

3. Speaker-Level Input Connector –

Use this connector for speaker level
input signals. A wire harness is
supplied for use with this
connector. See “Audio Input
Connections” section (page 23) for
wiring instructions. This input also
includes JBL’s Common Sense
input circuitry which turns the
amplifier on as soon as the high
powered head unit connected to
this input is turned on.

4. Speaker Output Connectors –

Connect speaker wiring to these
connectors. See wiring directions 
for more information.

5., 6., 7., 8. Power Connector –

Connection for power wires. See
wiring directions for information on
proper connections.

9. Fuses – Two 30 Amp ATC type 

fuses.

10. Gain Controls – Use these controls

to adjust the gain of the amplifier
channel group. See the “Adjusting
the Gain” section (on page 25) for
tips on proper setup.

11. Preamp Crossover Switches – These

switches control the built-in cross-
overs that are directed to the
preamp-output connectors. Set the
switch to F (flat) for full-band
operation for that group. Set the
switch to L (low) to activate the low-
pass filter on the pre-amp output
group (for subwoofer use or to use
in conjunction with a high-pass
filtered input signal to create a
bandpass crossover for a midrange
or midbass driver). Set the switch to
High-Pass to activate the high-pass
filter for use with satellite speakers
or tweeters on the pre-amp output
group.

12. Speaker Crossover Switches –

These switches control the built-in
crossovers that are connected to
each group's power amplifier cir-
cuitry. Set the switch to F (flat) for
full band operation on a group. Set
this switch to L (low) to activate the
low-pass filter on the selected
amplifier group for subwoofer use or

GTH400-20107  06/03/98 15:49  Side 9

10

to use in conjunction with a high-
pass filtered input signal to create a
bandpass crossover (for a midrange
or midbass driver). Set the switch to
H (high) to activate the high-pass
filter for use with satellite speakers or
tweeters on an amplifier group.

13. Mode Switches – These switches are

used to set the input mode for both
preamp and speaker-level inputs.
Set the switch to ST(ereo) for normal
operation on the group using
individual left and right inputs. Set
this switch to L to drive both the left
and right outputs with only a single
input on the left jack. Set the switch
to L+R to sum the left and right
inputs for a mono output on the
group. These switches do not affect
the preamp outputs.

14. Bass EQ Switch – These switches

activate a built-in Bass Boost  circuit
used to increase low-bass output on
the selected group. These switches
do not effect the preamp outputs.

15. Group 2 Input Switch – This switch is

used to select which inputs will drive
Group 2 of the amplifier. Put the
switch in position “GR 1” to allow
Group 2 to be driven by the Group 1
inputs. Put the switch in the “GR 2”
position to drive Group 2 with the
Group 2 inputs.

16. Group 3 Input Switch – This switch is

used to select which inputs will drive
Group 3 of the amplifier. Put the
switch in position “GR 3” to allow
Group 3 to be driven by the Group 3
inputs. Put the switch in the “GR 2”
position to drive Group 3 with the
Group 2 inputs. Put this switch in the
“GR 1+ 2” position to drive Group 3
with the sum of Group 1 and 2 for a

non-fading subwoofer output on
Group 3.

17. Remote Bypass/On Indicator – This

indicator is on when the Imaging
Enhancer is engaged and off when
the Imaging Enhancer is bypassed.

18. Driver/All Optimizer Indicator – This

indicator is on when the Virtual Center
Channel circuitry is in “Driver” opti-
mization mode and off when it is in
the “All” passenger mode. Note: The
enhancer on indicator must be on
before driver’s mode can enabled.

19. Front Ambience Control and

On/Bypass Switch – Rotating this
control adjusts the amount of
ambience and front staging width
produced by the Imaging Enhancer.
Pulling the knob places the Imaging
Enhancer in “Bypass” mode.
Pushing in the knob places the
Imaging Enhancer in “On” mode.

20. Rear Ambience and Driver/All

Optimizer Control – Rotating this
knob controls the amount of rear-fill
ambience and the “room size” of the
acoustic environment when used in
a system with rear speakers. Pulling
the knob out places the Imaging
Enhancer in “All” passengers opti-
mization mode. Pushing the knob in
places the unit in “Driver” optimizati-
on mode. Best results at the driver’s
position will be achieved with the
control in the “Driver” setting.

Power Indicator LED (on amp chassis
top) – LED steadily illuminates for normal
operation. LED blinks when protection
circuitry or muting is engaged.

19

20

17

18

MIN

MAX

BYPASS

ENHANCER 

ON

IMAGING ENHANCER

ENHANCER  ON

DRIVER MODE

FRONT AMBIENCE

REAR AMBIENCE

ALL

DRIVER

MIN

MAX

GTH400-20107  06/03/98 15:49  Side 10

11

+

-

+

-

+

-

Buffer

Buffer

Buffer

Buffer

Buffer

Buffer

1

2

3

1

2

3

1

2

3

1

2

1

2

1

2

3

1

2

3

1 2

3

1

2

3

CH. 1 L IN

CH. 1 R IN

CH. 2 L IN

CH. 2 R IN

CH. 1 L OUT

CH. 1 R OUT

CH. 2 L OUT

CH. 2 R OUT

IMAGE

ENH.

1

2

3

GROUP 3 

INPUT

+

+

1 – GR 3

2 – GR 2

3 – GR 1+2

1

Speaker

Crossover

1 – Flat

2 – Low Pass

3 – High Pass

Preamp

Crossover

1 – Flat

2 – Low Pass

3 – High Pass

GR 3

Input Mode

∑

∑

+

+

GR 1

GR 2

GR 3

L

L

L

R

R

Buffer

Buffer

Buffer

Buffer

GR 1

GR 2

L

L

R

R

R

LP

HP

GR 1 L

PREOUT

X-OVER

GR 1  MODE SWITCH

GR 2  MODE SWITCH

1

2

3

1

2

3

LP

HP

GR 1 R

PREOUT

X-OVER

1

3

2

1

2

3

LP

HP

GR 2 L

PREOUT

X-OVER

1

3

2

1

2

3

LP

HP

GR 2 R

PREOUT

X-OVER

1

3

2

1

2

3

LP

HP

GR 3 L

PREOUT

X-OVER

1

3

2

1

2

3

LP

HP

GR 3 R

PREOUT

GR 3 Left Speaker Out

GR 3 Right Speaker Out

X-OVER

1

3

2

1

3

2

1

3

2

1

3

2

BASS BOOST

AMP

AMP

GR 2 Left Speaker Out

GR 2 Right Speaker Out

BASS BOOST

AMP

AMP

1

3

2

1

3

2

GR 1 Left Speaker Out

GR 1 Right Speaker Out

BASS BOOST

AMP

AMP

❶

❶

❶

❶

❷

❷

❷

❷

∑

∑

∑

∑

Mode

1 – L

2 – Stereo

3 – L+R

❸

GROUP 2 

INPUT

1 – GR 1

2 – GR 2

❸

❸

❸

Buffer

Buffer

Buffer

Buffer

Buffer

Buffer

Speaker-level

inputs

Preamp-level inputs

+

-

Buffer

+

+

+

+

GTH400-20107  06/03/98 15:49  Side 11