Infinity 7520a Service manual

Reference Series

7520a

2 CHANNEL POWER AMPLIFIER

SERVICE MANUAL

Infinity Systems, Inc.

250 Crossways Park Dr.

Woodbury, New York 11797 Rev0 5/2004

Power Amplifier Reference 7520a

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- 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

IC/TRANSISTOR PINOUTS..……………………….. …..17

SCHEMATICS………..……………………….…………...19

PACKING……..…………………………………………....21

Referen ce 75 20a 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: 240mV

DC Offset <50mV (-50%)

Output regulation: .078dB @ 4 ohms

Idle Current 900mA

Input Impedance 22kΩ

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.

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The Reference amplifiers are capable of
delivering high power levels, and require a
reliable connection to the vehicle’s electrical
system in order to perform optimally. See
Figure 1 for connection location. Please
adhere to the following instructions carefully.

GROUND CONNECTION

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.

POWER CONNECTION

Connect a wire (see chart at right for appropriate
gauge) directly to the vehicle’s positive battery
terminal, and install an appropriate fuse holder
within 18" of the battery terminal. Do not
install the fuse at this time. Route the wire to
the amplifier’s location, and connect it to the
amplifier’s positive (+12V) terminal. Be sure to
use appropriate grommets whenever routing
wires through the firewall or other sheet metal.
Failure to adequately protect the positive wire
from potential damage may result in a vehicle
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
fuse value should be selected based on total
amplifier-current draw; see chart at right.

REMOTE CONNECTION

Connect the amplifier’s Remote (REMOTE)
terminal to the source unit’s Remote Turn-On
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)
terminal to the vehicle’s accessory circuit.

WIRE-GAUGE CHART

Amplifier Maximum Minimum
Model Current Draw Wire Gauge

7520a 34A #8 AWG
7540a 85A #8 AWG
5760a 87A #8 AWG
310a 40A #8 AWG
610a 69A #6 AWG
1210a 115A #4 AWG

These recommendations assume 7' – 10' wire
runs. If your installation differs markedly, you
will need to adjust the wire gauge accordingly.

SPEAKER CONNECTIONS

Refer to the application guides on the pages
that follow. Speaker connections should be
made using a minimum of 16-gauge wire.

HIGH-LEVEL INPUT CONNECTIONS

The 7520a, 7540a and 5760a amplifiers are
equipped with speaker-level inputs that allow
you to add an amplifier to head units that do
not have RCA line outputs. The speaker outputs
for the source unit should be connected to the
amplifier using the supplied connector (square
four-wire plug). Remember to check for proper
polarity. The 310a, 610a and 1210a amplifiers
are not equipped with high-level inputs.

NOTE: When using the low-level or high-level
inputs, the AUX outputs can be used to pass a
full-range line-level signal to another amplifier.

Figure 2. Speaker-level connector.

POWER CONNECTIONS

HIGH LEVEL

INPUT

Speaker Wires

(spliced)

LR

–
L
+

–
R
+

+ WHITE

– WHITE/BLACK

GRAY/BLACK –

GRAY +

Power Amplifier Reference 7520a

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Figure 1.Terminal-connection end plate.

The 7520a 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.

APPLICATIONS – 7520a

Figure 5. 7520a amplifier set up for stereo operation.

Figure 6. 7520a amplifier set up for bridged-mono operation.

Power Amplifier Reference 7520a

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Initially set the crossover-frequency control
midway. While listening to music, adjust the
crossover for the least perceived distortion from
the speakers, allowing them to reproduce as
much bass as possible.

Systems using a separate subwoofer set the
crossover mode to HP (high pass) for your
full-range speakers. Adjust the crossover
frequency to limit bass, and provide increased
system volume with less distortion.

For subwoofers, choose the highest frequency
that removes vocal information from the sound
of the subwoofer.

If using the 7520a or 7540a to drive a subwoofer(s),
set the crossover mode to LP (low pass).

NOTE:The 310a, 610a, 1210a and the subwoofer
output of the 5760a are low-pass only and do not
have a crossover-mode switch.

SETTING THE CROSSOVER(S)

Determine your system plans and set the
crossover-mode switch accordingly. If your
system design does not include a subwoofer,
set the crossover mode to FLAT and skip to
“Setting Input Sensitivity.”

MODE SWITCH
Flat: Allows a full-range signal through to the

speakers; can be used with larger full-range
speakers such as 6" x 9"s.
HP: Allows a high-pass signal through to
the speakers; should be used with most
loudspeakers (can protect your full-range
speakers from being overdriven with low
frequencies, one cause of speaker damage).
LP: Allows bass to pass through to the speakers;
should be selected when powering subwoofers.

Figure 13. Control end panel.

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
and play a dynamic music track.

3. On the source unit, increase the volume

control to 3/4 volume. Slowly increase the
INPUT LEVEL control(s) toward three o’clock
until you hear slight distortion in the music.
Then reduce the INPUT LEVEL slightly until
distortion is no longer heard.

NOTE: After the source unit is on, blue LEDs (on
the top panel) will light, indicating the amplifier
is on. If not, check the wiring, especially the
remote connection from the source unit. Also
refer to “Troubleshooting” on the page 7.

INSTALLATION AND SETUP

7520a

REMOTE LEVEL CONTROL (OPTIONAL)

All three Reference subwoofer amplifiers and
the 5760a amplifier have inputs for an optional
remote level control (100rc). This will allow the
subwoofer level to be adjusted from the listening
position. Connect the optional remote level
control using the RJ-11 jack on the side of the
amplifier. Install the control module in the front
of the vehicle within easy reach of the driver.
Both the underside of the dash and the center
console are suitable locations. Refer to the
mounting instructions accompanying the 100rc.

SETTING THE BASS BOOST

The 7520a, 7540a and 5760a are all equipped
with a bass-boost control. This allows you to
enhance the bass output of your system at
50Hz up to 12dB.

NOTE: Only rear channels of the 7540a are
affected by the bass boost control.

AUX OUTPUT

Reference amplifiers (except 5760a) 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.

Power Amplifier Reference 7520a

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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.

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PROBLEM:

No audio (POWER LED is off).

CAUSE and SOLUTION:
No voltage at BATT+ and/or REM terminals, or
bad or no ground connection. Check voltages
at amplifier terminals with VOM.

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PROBLEM:

No audio (PROTECT LED flashes every
4 seconds).

CAUSE and SOLUTION:
DC voltage on amplifier output. Amplifier may
need service; see enclosed warranty card for
service information.

•

PROBLEM:

No audio (PROTECT LED is on).

CAUSE and SOLUTION:
Amplifier is overheated. Make sure amplifier
cooling is not blocked at mounting location;
verify that speaker-system impedance is within
specified limits.

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PROBLEM:

No audio (PROTECT and POWER LEDs flash).

CAUSE and SOLUTION:
Voltage less than 9V on BATT+ connection.
Check vehicle charging system.

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PROBLEM:

No audio (PROTECT LED is on).

CAUSE and SOLUTION:
Voltage greater than 16V or less than 8.5V on
BATT+ connection. Check vehicle charging
system.

•

PROBLEM:

Distorted audio.

CAUSE and SOLUTION:
Input sensitivity is not set properly, or amplifier
or source unit is defective. Check INPUT LEVEL
setting, or check speaker wires for shorts or
grounds.

•

PROBLEM:

Distorted audio (PROTECT LED flashes).

CAUSE and SOLUTION:
Short circuit in speaker or wire. Remove
speaker leads one at a time to locate shorted
speaker or wire, then repair.

•

PROBLEM:

Music lacks “punch.”

CAUSE and SOLUTION:
Speakers are not connected properly. Check
speaker connections for proper polarity.

TROUBLESHOOTING

Power Amplifier Reference 7520a

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