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Reference Series
7540a
7541a
4 CHANNEL POWER AMPLIFIER

SERVICE MANUAL




Infinity Systems, Inc.
250 Crossways Park Dr.
Woodbury, New York 11797 Rev3 10/2005
Power Amplifier Reference 7540a/7541a

- CONTENTS -

SPECIFICATIONS ................................................1
FEATURES/TEST CONDITIONS.............................2
CONTROLS/CONNECTIONS...................................3
INSTALLATION......................................................5
BASIC TROUBLESHOOTING..................................6
TYPICAL SYSTEM WIRING....................................7
EXPLODED VIEW/PARTS LIST...............................8
MECHANICAL PARTS LIST.....................................9
AMPLIFIER BLOCK DIAGRAM..............................10
P.C.B. DRAWINGS...............................................11
ELECTRICAL PARTS LIST .................................. 15
REF 7541a ELECTRICAL PARTS LIST ADDENDUM..........18
IC/TRANSISTOR PINOUTS.............................. .....19
REF 7540a SCHEMATICS.....................................22
REF 7541a SCHEMATICS.....................................25
PACKING...........................................................28

Reference 7540a/7541a Specifications

Output Power: 111W RMS x 4 channels @ 4 ohms; 1% THD + N
(14.4V supply) 139W RMS x 4 channels @ 2 ohms; 1% THD + N
278W RMS x 2 channels @ 4 ohms; 1% THD + N
Signal-to-noise ratio: 81dBA (reference 1W into 4 ohms)
Dynamic power: 164W @ 2 ohms
Effective damping factor: 6.315 @ 4 ohms
Frequency response: 10Hz ­ 100kHz (­3dB)
Maximum input signal: 5.5V
Maximum sensitivity: Reference 7540a - 230mV
Reference 7541a - 75mV
DC Offset <50mV (-50%)
Output regulation: .088dB @ 4 ohms
Idle Current 1.2A
Input Impedance 22k
Max Current Draw 54A @ 4 ohms
83A @ 2 ohms
Dimensions: 12 x 15 x 2 11/16" (L x W x D)
(305mm x 381mm x 68mm)
Fuses: 30A x 2


Infinity continually strives to update and improve existing products, as well as create new ones. The specifications and details in
this and related JBL publications are therefore subject to change without notice.




1
Reference 7540a/7541a




2
Power Amplifier Reference 7540a/7541a
POWER CONNECTIONS
The Reference amplifiers are capable of WIRE-GAUGE CHART
delivering high power levels, and require a Amplifier Maximum Minimum
reliable connection to the vehicle's electrical Model Current Draw Wire Gauge
system in order to perform optimally. See 7520a 34A #8 AWG
Figure 1 for connection location. Please 7540a/7541a 85A #8 AWG
adhere to the following instructions carefully. These recommendations assume 7' ­ 10' wire
GROUND CONNECTION runs. If your installation differs markedly, you
Connect the amplifier's Ground (GND) terminal will need to adjust the wire gauge accordingly.
to a solid point on the vehicle's metal chassis,
as close to the amplifier as possible. Refer to the
chart below to determine minimum wire-gauge
size. Sand away any paint from this location; use
a star-type-lock washer to secure the connection. SPEAKER CONNECTIONS
Refer to the application guides on the pages
POWER CONNECTION that follow. Speaker connections should be
Connect a wire (see chart at right for appropriate made using a minimum of 16-gauge wire.
gauge) directly to the vehicle's positive battery
terminal, and install an appropriate fuse holder HIGH-LEVEL INPUT CONNECTIONS
within 18" of the battery terminal. Do not The 7540a/7541a amplifiers are
install the fuse at this time. Route the wire to equipped with speaker-level inputs that allow
the amplifier's location, and connect it to the you to add an amplifier to head units that do
amplifier's positive (+12V) terminal. Be sure to not have RCA line outputs. The speaker outputs
use appropriate grommets whenever routing for the source unit should be connected to the
wires through the firewall or other sheet metal. amplifier using the supplied connector (square
Failure to adequately protect the positive wire four-wire plug). Remember to check for proper
from potential damage may result in a vehicle polarity.
fire. When you are done routing and connecting
this wire to the battery and to the amplifier,
you may install the fuse at the battery. The NOTE: When using the low-level or high-level
fuse value should be selected based on total inputs, the AUX outputs can be used to pass a
amplifier-current draw; see chart at right. full-range line-level signal to another amplifier.
REMOTE CONNECTION Figure 2. Speaker-level connector.
Connect the amplifier's Remote (REMOTE)
terminal to the source unit's Remote Turn-On HIGH LEVEL
INPUT
lead using a minimum of 18-gauge wire. If your
source unit does not have a remote turn-on ­ ­
connection, connect the amplifier's (REMOTE) L R
terminal to the vehicle's accessory circuit. + +

GRAY + ­ WHITE/BLACK
GRAY/BLACK ­ + WHITE

R L
Speaker Wires
Figure 1.Terminal-connection end plate. (spliced)




3
Power Amplifier Reference 7540a/7541a

APPLICATIONS ­ 7540a/7541a
The 7540a/7541a can be set up for stereo 4-channel,
3-channel or bridged 2-channel operation, as
shown in Figures 7 through 9.

NOTE: For simplicity, Figures 7 through 9 do not
show power, remote and input connections.

NOTE: Minimum speaker impedance for
stereo operation is 2 ohms. Minimum speaker
impedance for bridged operation is 4 ohms.

NOTE: "Bass Boost" only affects rear channels.




Figure 7. 7540a/7541a amplifier in 4-channel (stereo) operation to drive front and rear full-range speakers.




Figure 8. 7540a/7541a is set up for 3-channel operation to drive a set of full-range speakers and a subwoofer.




Figure 9. 7540a/7541a used in bridged 2-channel mode to drive a set of components or subwoofers.
4
Power Amplifier Reference 7540a/7541a
INSTALLATION AND SETUP
SETTING THE CROSSOVER(S) Initially set the crossover-frequency control
Determine your system plans and set the midway. While listening to music, adjust the
crossover-mode switch accordingly. If your crossover for the least perceived distortion from
system design does not include a subwoofer, the speakers, allowing them to reproduce as
set the crossover mode to FLAT and skip to much bass as possible.
"Setting Input Sensitivity.
"
Systems using a separate subwoofer set the
MODE SWITCH crossover mode to HP (high pass) for your
Flat: Allows a full-range signal through to the full-range speakers. Adjust the crossover
speakers; can be used with larger full-range frequency to limit bass, and provide increased
speakers such as 6" x 9"s. system volume with less distortion.
HP: Allows a high-pass signal through to
the speakers; should be used with most For subwoofers, choose the highest frequency
loudspeakers (can protect your full-range that removes vocal information from the sound
speakers from being overdriven with low of the subwoofer.
frequencies, one cause of speaker damage).
LP: Allows bass to pass through to the speakers; If using the 7540a/7541a to drive a subwoofer(s),
should be selected when powering subwoofers. set the crossover mode to LP (low pass).


SETTING INPUT SENSITIVITY
1. Initially turn the INPUT LEVEL control(s) to
minimum (counterclockwise).
2. Reconnect the (­) negative lead to the vehi- REMOTE LEVEL CONTROL (OPTIONAL)
cle's battery. Apply power to the audio system All three Reference subwoofer amplifiers
and play a dynamic music track. have inputs for an optional
3. On the source unit, increase the volume remote level control (100rc). This will allow the
control to 3/4 volume. Slowly increase the subwoofer level to be adjusted from the listening
INPUT LEVEL control(s) toward three o'clock position. Connect the optional remote level
until you hear slight distortion in the music. control using the RJ-11 jack on the side of the
Then reduce the INPUT LEVEL slightly until amplifier. Install the control module in the front
distortion is no longer heard. of the vehicle within easy reach of the driver.
Both the underside of the dash and the center
NOTE: After the source unit is on, blue LEDs (on console are suitable locations. Refer to the
the top panel) will light, indicating the amplifier mounting instructions accompanying the 100rc.
is on. If not, check the wiring, especially the
remote connection from the source unit. Also SETTING THE BASS BOOST
refer to "Troubleshooting" on the page 6. The 7540a/7541a are all equipped
with a bass-boost control. This allows you to
AUX OUTPUT
enhance the bass output of your system at
Reference amplifiers are equipped
50Hz up to 12dB.
with full-range outputs that can be used to
connect additional amplifiers.
NOTE: Only rear channels of the 7540a/7541a are
affected by the bass boost control.
NOTE: When using the low- or high-level inputs,
the AUX outputs can be used to pass a full-range
line-level signal to another amplifier.


Figure 13. Control end panel.




5
Power Amplifier Reference 7540a/7541a
TROUBLESHOOTING
· PROBLEM: · PROBLEM:
No audio (POWER LED is off). No audio (PROTECT LED is on).

CAUSE and SOLUTION: CAUSE and SOLUTION:
No voltage at BATT+ and/or REM terminals, or Voltage greater than 16V or less than 8.5V on
bad or no ground connection. Check voltages BATT+ connection. Check vehicle charging
at amplifier terminals with VOM. system.


· PROBLEM: · PROBLEM:
No audio (PROTECT LED flashes every Distorted audio.
4 seconds).
CAUSE and SOLUTION:
CAUSE and SOLUTION: Input sensitivity is not set properly, or amplifier
DC voltage on amplifier output. Amplifier may or source unit is defective. Check INPUT LEVEL
need service; see enclosed warranty card for setting, or check speaker wires for shorts or
service information. grounds.


· PROBLEM: · PROBLEM:
No audio (PROTECT LED is on). Distorted audio (PROTECT LED flashes).

CAUSE and SOLUTION: CAUSE and SOLUTION:
Amplifier is overheated. Make sure amplifier Short circuit in speaker or wire. Remove
cooling is not blocked at mounting location; speaker leads one at a time to locate shorted
verify that speaker-system impedance is within speaker or wire, then repair.
specified limits.

· PROBLEM:
· PROBLEM: Music lacks "punch.
"
No audio (PROTECT and POWER LEDs flash).
CAUSE and SOLUTION:
CAUSE and SOLUTION: Speakers are not connected properly. Check
Voltage less than 9V on BATT+ connection. speaker connections for proper polarity.
Check vehicle charging system.

STATUS LEDs
Clip: Indicates the amplifier is being overdriven,
and your speakers may be in danger. This
should blink only on musical peaks, and not
be on constantly.
Power: Indicates the amplifier is on.
Protection: Refer to "Troubleshooting" for specific
indications.
Figure 15. LED status.




6
Reference 7540a/7541a




7
Reference 7540a/7541a




A




B




C




D




E


8
1 2 3 4 5 6 7 8
Power Amplifier Reference 7540a/7541a




9
Power Amplifier Reference 7540a/7541a


7540a/7541a BLOCK DIAGRAM




10
Reference 7540a/7541a




35m/m
J43 7.5m/m
J42
J29 TM0006-01




W2 105(M)TL
WT-9519




60m/m
WIRE
J30
7.5m/m




7.5m/m
TER02 WF-9604
7.5m/m
7.5m/m




IN4004
L/CH 7.5m/m
R/CH




D02
FH01 J31 BJ06 105(M)"TL"




BJ09
J32
R262 C01
35m/m




J41 7.5m/m
J40
10m/m
10m/m
10m/m
10m/m
10m/m
10m/m

6m/m
680/2W
680/2W
20m/m
1N5404 08




J33
6m/m
D01




7.5m/m
47
104(M) BJ




FQP50N06
4.7/0.5W R56




R04
56K
R362 C03 104P




J300
17.5m/m




4.7/0.5W
R261 C261 J05




R361




J39
J38
17.5m/mJ06




J37
J36
J35
J34
680/2W




55m/m
55m/m
R462 C3198GR 1K




7.5m/m
7.5m/m
R92
Q02
4.7/0.5W




J323
J322
430K R63 Q56
104(M) 8.2K




104(M)
R461 Q90C3198GR 47




C461




FQP50N06
C361 R05 R55
4.7K 2200/25V"WL"




CL-310
A1266GR 17.5m/m
J07




100/16V
680/2W R91 Q11 22K R11
C05 17.5m/m
J08
R90 47K 3.9K




104(M)
R162
10 R12 C11




J310
C161 R15 47/16V Q55
104P C60
R161 C14 47




FQP50N06
J53 6m/m R54




L03
4.7KF




20m/m




10m/m
10m/m
4.7/0.5W 10K R62 J09
17.5m/m
A1266GRR13
Q12 10.5KF




J21
17.5m/m
J10




J22
24K J52 6m/m R60 2200/25V"WL"
R21 6m/m 1SS133 C04
20m/m J111 D03 1K
R52 Q54
J54 A1266GR Q33




12.5m/m J50
12.5m/m J49
12.5m/m J48
12.5m/m J47
12.5m/m J46
12.5m/m J45
12.5m/m J44
473P
C32 WIRE C12 100/16V 47 R53




FQP50N06
TL494CN
17.5m/m
J11




10m/m
10m/m35m/m
220/0.5W
120m/m R51 17.5m/m
J12
220/0.5W




J24
J23
68K
W1



200K
R369
R25 A1266GR R41
105(M)TL 102(M) Q23
200K C21 2200/25V"WL" Q53
D269C31D369 24K 1SS133
R269 R22 7.5m/m




BJ04
1SS133 1SS133 15m/m D04 C06 7.5m/m




J3 25
J55 6m/m U01 J51 7.5m/m
LWL0640-02P




1SS133 1SS133




J 26
31
J
200K D469 R16 820
D169 200K 10/16V
CLIP




R469 R169 4.7K C800 7.5m/m
R02 R46
A1023Y 7.5m/m 47




10m/m
10m/m
10m/m




FQP50N06
C3198BL Q01
17.5m/m J13
BK




Q21




J228
4.7K