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Reference Series
7520a
7521a
2 CHANNEL POWER AMPLIFIER
SERVICE MANUAL




Infinity Systems, Inc.
250 Crossways Park Dr.
Woodbury, New York 11797 Rev3aa10/2005
Power Amplifier Reference 7520a/7521a

- 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 .................................. 14
REF 7521a ELECTRICAL PARTS LIST ADDENDUM..........17
IC/TRANSISTOR PINOUTS....................................18
REF 7520a SCHEMATICS.....................................20
REF 7521a SCHEMATICS.....................................22
PACKING...........................................................24

Reference 7520a/7521a Specifications

Output Power: 97W RMS x 2 channels @ 4 ohms; 1% THD + N
(14.4V supply) 142W RMS x 2 channels @ 2 ohms; 1% THD + N
283W RMS x 1 channels @ 4 ohms; 1% THD + N
Signal-to-noise ratio: 83dBA (reference 1W into 4 ohms)
Dynamic power: 190W @ 2 ohms
Effective damping factor: 6.389 @ 4 ohms
Frequency response: 10Hz ­ 69kHz (­3dB)
Maximum input signal: 5.5V
Maximum sensitivity: Reference 7520a - 240mV
Reference 7521a - 75mV
DC Offset <50mV (-50%)
Output regulation: .078dB @ 4 ohms
Idle Current 900mA
Input Impedance 22k
Max Current Draw 22A @ 4 ohms
37A @ 2 ohms
Dimensions: 12 x 11 7/16 x 2 11/16" (L x W x D)
(305mm x 290mm x 68mm)
Fuse: 30A

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 7520a/7521a




2
Power Amplifier Reference 7520a/7521a
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/7521a 34A #8 AWG
Figure 1 for connection location. Please
adhere to the following instructions carefully. These recommendations assume 7' ­ 10' wire
runs. If your installation differs markedly, you
GROUND CONNECTION
will need to adjust the wire gauge accordingly.
Connect the amplifier's Ground (GND) terminal
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 7520a/7521a 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 7520a/7521a

APPLICATIONS ­ 7520a/7521a
This amplifier can be set up for stereo or
bridged-mono operation, as shown in Figures 5
and 6.

NOTE: For simplicity, Figures 5 and 6 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.




Figure 5. Amplifier set up for stereo operation.




Figure 6. Amplifier set up for bridged-mono operation.




4
Power Amplifier Reference 7520a/7521a
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 7520a/7521a 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-
cle's battery. Apply power to the audio system REMOTE LEVEL CONTROL (OPTIONAL)
and play a dynamic music track. All three Reference subwoofer amplifiers
3. On the source unit, increase the volume have inputs for an optional
control to 3/4 volume. Slowly increase the remote level control (100rc). This will allow the
INPUT LEVEL control(s) toward three o'clock subwoofer level to be adjusted from the listening
until you hear slight distortion in the music. position. Connect the optional remote level
Then reduce the INPUT LEVEL slightly until control using the RJ-11 jack on the side of the
distortion is no longer heard. amplifier. Install the control module in the front
of the vehicle within easy reach of the driver.
NOTE: After the source unit is on, blue LEDs (on Both the underside of the dash and the center
the top panel) will light, indicating the amplifier console are suitable locations. Refer to the
is on. If not, check the wiring, especially the mounting instructions accompanying the 100rc.
remote connection from the source unit. Also SETTING THE BASS BOOST
refer to "Troubleshooting" on the page 6. The 7520a/7521a is equipped
with a bass-boost control. This allows you to
enhance the bass output of your system at
AUX OUTPUT 50Hz up to 12dB.
These amplifiers are equipped
with full-range outputs that can be used to
connect additional amplifiers.

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 7520a/7521a

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 7520a/7521a




7
Reference 7520a/7521a




A




B




C




D




E



1 2 3 4 5 6 7 8
8
Power Amplifier Reference 7520a/7521a

Mechanical Parts List




9
Power Amplifier Reference 7520a/7521a




REF 7520a/7521a BLOCK DIAGRAM




10
Reference 7520a/7521a




V-CUT TER02 FH01 V-CUT
TM0009-01 56K
TM0006-01
R04 J01




47/16V
TER01




J312
J311
J310
J02
7.5m/m




6m/m
6m/m
J180
6m/m
6m/m
J181
6m/m
WF-9402P 7.5m/m
J03
7.5m/m
J04




105(M)"TL"
C11
7.5m/m
J335
C3198GR




IN4004
1K Q02 10m/m
J336




6m/m
7.5m/m
7.5m/m
7.5m/m
7.5m/m
7.5m/m
J314
J313


J11
10m/m




J13
J12

J10
R92 8.2K
680/2W R05




R63 430K
R11 4.7K
680/2W C3198GR A1266GR 7.5m/m J315




C01

D02
7.5m/m J316 C801
R262 R162 Q90 Q11 473P
R261 4.7/0.5W 22K 7.5m/m
4.7/0.5W R91 3.9K J317
104(M) 104(M) C161R161 R9047K R12 1N5404
10 47/16V D01
C261 C14
R15 104P
J186m/m R13 10K




CL-300
C60 C04
A1266GR 100/16V R62 4.7KF
Q12




L03
C17 10.5KF
24K R60
R21 U01
J156m/m
17.5m/m J16 6m/m 2200/25V"WL"
1SS133
SCREW
105(M)TL


J19 100/16V D03
C12 A1266GR 104P C03
C32 60m/m




TL494CN
Q33
68K 220/0.5W
R25 R51 C05




J06 17.5m/m
J05 17.5m/m
7.5m/m
7.5m/m
102(M)
WIRE




220/0.5W




J319
J318
C21 R41
W1




R168
100K


24K A1266GR




J092.5m/m
J08
J07
105(M)TL R22 R54
100K




Q23
R268




47




12.5m/m
12.5m/m
1
SCREW




FQP50N06
6m/m 1SS133
C31




J17 2200/25V"WL" 20m/m J75
1SS133 750 D0415m/m
R16 20m/m J76
1SS133 D168 4.7K 10/16V J14




7.5m/m2
7.5m/m
7.5m/m
7.5m/m
R02 C800 10/0.5W R52
D268




J322

J321
J320
R03 1K




J323
C3198BL 4.7K Q54
CLIP




Q21 R01 R53
47
2P




FQP50N06
10K A1023Y 20m/m
R14 Q01 J77




3
15m/m J78
BK




6m/m 20m/m
J341 J340 104P
C22 100/16V
1K
R31 C13 Q53


4
R44




1
22K
1STPOWER




1SS133


(0.7x9):(0.7x4)
47




FQP50N06
D11 R32 J79
17.5m/m
10/25V R33 33K
RED
3P




17.5m/mJ80

5T:12T
C15 A1268GR
10m/m
10m/m




15K
J331
J330




R35 Q22
1K R42
BK




15K T01




37PHI
47/25V R34 R43 Q44
YG225D2




C16 47




FQP50N06
J53




25m/m J22
J52




17.5m/mJ81
25m/m J23
12.5m/m
12.5m/m




17.5m/mJ82
J58
1000/35V"SHL"




D41 25m/m J24
25m/m SCREW Q43
J25
25m/m




FTD5-350
CL-500




5




473P C33

TH01
8
YG225D2




10K R61
C51




25m/m J26
J552.5m/m
J54




222(M)
25m/m J27 10m/m



100/2W
6




C08
7
1
12.5m/m




J56
12.5m/m J28 J57 10m/m
L01




R30
1000/35V"SHL"




D42
15m/m
12.5m/m J29
12.5m/m J30 7520a
J43 J42 12.5m/m12.5m/m J31
FR154
FR154

FR154

FR154

47/50V 47/50V
D54

D53

D52
12.5m/m J32




D51
J4112.5m/m
473P




15m/m
15m/m




Q181
C61




C67
7.5m/m 10m/m J33
CL-500
C3198GRJ40
C63




7.5m/m 12.5m/m J34
473P
L02




C53




Q281 J39 3300/35V"SHL"




C57
C3198GR 3300/35V"SHL"
R181
J59




10m/m J35
100/16V




10m/m
10m/m




10m/m J36
J62
J6322m/m




C62
56K




C52




10m/m J37
330/2W
J342 15m/m




J68
J69




330/2W
R291


R191




10m/m J38
C181
J64
J65
22m/m




17.5m/m




R281
22m/m




J66



J67




56K
15m/m J101
15m/m




15m/m J102
6m/m
20m/m J103 7.5m/m J70 J73 J74
C3200GR 1.5K6m/m 2.2/50V C3200GR 1.5K
22m/m J104 Q251 R251 C141
2.2/50V Q151 15K R151
2NDPOWER