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4. In some systems it may be desirable to

have two sources play simultaneously
through the audio system . For instance, if
you have a factory installed radio in your
car, and you want to add an aftermarket
CD player, you may connect the CD player
to the RCA inputs of the amp, and the
factory radio to the Universal Interface
Speaker Inputs. Note: Front and rear
channels of the CD and radio must be
driven into the front and rear inputs of the
amplifier. Use Y adapters if necessary. The
Universal Interface circuitry will isolate the
two signals from each other while
allowing them to drive the amp
simultaneously. Therefore switching from
one source to the other is as simple as
turning the unused source off, and the
other on. (Note: you must connect the
remote turn-on wire from the CD player to
the Rem terminal on the amp. Install a
diode in the remote line from the CD
player as shown in the diagram below.)

Electronic Crossover
The electronic crossover in the P-4020 and
P4040 should be used to route the
appropriate signal to speakers intended to
play only bass, or only midrange and treble
frequencies. The crossover slope is 12dB/oct
and the frequency is fixed at 80Hz. 
Pre-amp Outputs
Connect these to the input connectors of
other amplifiers or processors in your
system. Refer to the Applications section for
system expansion possibilities.
Setting Input Sensitivity
Proper input sensitivity control settings on
Power Series amplifiers are critical to ensure
optimum performance, low noise levels and
maximum system reliability. As a general
rule, controls at the front end of a system
(source, equalizers, and other processors
should be set as high as possible with the
amplifier input sensitivity set as low as
possible while still providing adequate
volume levels. Using a high signal level and
a low sensitivity setting will help keep
background noise in the system to a
minimum.

Initially, turn the input sensitivity GAIN
control to its minimum (counter-clockwise)
position.

1. Reconnect the (–) negative lead to your

vehicle's battery. Apply power to the audio
system and play a favorite music track
from CD or tape. 
NOTE: After the source unit is on, the JBL
badge (on the top panel) will illuminate,
indicating the amplifier is on. If not, check
the wiring, especially the remote
connection from the source unit. Also refer
to Troubleshooting on page 7.

2. On the source unit, increase the volume

control until it is approximately 3/4 of its
maximum output level. Slowly increase
the Input Sensitivity control (clockwise)
towards three o clock and, at the same
time, listen to the quality of the
reproduced sound. At some point, you'll
hear distortion on the music peaks. Stop
the adjustment and turn it back slightly.
This is the maximum undistorted output
level of your system, and should not be
exceeded during use. 

3. After adjusting the level of the main

speakers in your system, you should
adjust the remaining channels (if you are
using a P-4040 or a multi-amp system) for
the desired system balance. You'll find this
easiest to do by adjusting the channels in
the following order: 1) front speakers, 
2) rear speakers, 3) subwoofer. Elaborate,
multi-channel systems may be complex to
adjust. Your local JBL installation specialist
is the best person to help with such
adjustment. 

For your convenience, we've included
several application diagrams to help you
plan your own system installation. Figures 1
through 3 show how to configure the JBL 
P-4020 or P-4040 for stereo, bridged-mono,
and tri-mode operation. 
For system expansion ideas, see Figures 4
and 5 on the next page. 
NOTE: For simplicity, Figures 1 through 3 do
not show power, remote, and input
connections.

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6

20

30

20

20

Figure 1. This wiring diagram shows a
JBL P-4020/4040 amplifier set to stereo
to drive a pair of full-range speakers.

Figure 2. This wiring diagram shows
a JBL P-4020/4040 amplifier set to
bridge mode (mono) to drive a single
subwoofer.

Figure 3. This wiring diagram shows
a JBL P-4020/4040 amplifier set for 
tri-mode operation. For a desired
crossover frequency, use the chart on
page 4 to select a inductor for the
subwoofer, and corresponding
capacitors for left and right speakers.

Figure 4. In this example system, a
JBL P-4040 drives a pair of 5-1/4”
speakers. The JBL P-4020s stereo
low-pass outputs feed a bridged-
mono JBL P-4040 to drive a single
12” subwoofer.

Figure 5. In this expanded system, a JBL P-4040 drives two pairs of 6-1/2 2-way speakers. 
The JBL P-4040s pre-amp outputs feed a JBL P-4020 to drive a single 12” subwoofer in bridge
mode.

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7

No audio

Low/no remote on voltage

Check connections; test turn-on voltage

Speakers are not connected or are blown

Check wiring; use VOM/DVM to measure speaker coil 
resistance

Distorted audio

Input sensitivity is not set properly

See Setting Input Sensitivity on page 5

Audio lacks “punch”

Speakers are wired with wrong polarity

Check polarity of connections; refer to Applications

Audio cycles off and on;

A protection circuit is turning the 

Verify the following: voltage of electrical system is

amber protection LED 

amplifier off and on

between 5 ~ 18Vdc; temperature is not 

(JBL badge on top panel)

over 194°F (90°C); no short circuits; speaker 

is flashing

loads are not less than 2 ohms (4 ohms in mono)

Audio cycles off and on;

GAIN is set too high

Set Input Sensitivity

amber protection LED

correctly (see page 5)

(on top panel) is flashing

Fuse blows

Incorrect wiring or short circuit

Check connections; refer to Applications

Many different system configurations are
possible using the crossovers and pre-amp
outputs featured in Power Series amplifiers.
If you are considering expanding you system
beyond what is shown here, please consult
your local JBL installation specialist who is
experienced in designing complex mobile
audio systems. 

Use the following guide to identify
symptoms and solve problems. Make sure
the vehicles electrical system is working
properly and power is reaching the JBL 
P-4020 P-4040.

Declaration of Conformity

Kongevejen 194B 
DK-3460 Birkerød
DENMARK

declare in own responsibility, that the products  

  described

in this owner’s manual are in compliance with technical

 

standard:

EN 55 013/8.1994

Steen Michaelsen

Birkerød. DENMARK. 8/98

EN 55 020/12. 1994

EN 55 013/A12/8. 1994

EN 55 020/12.1994

Birkerød, DENMARK. 10/98

JBL Consumer Products
250 Crossways Park Drive
Woodbury, NY 11797
www.jbl.com

Part No. SH1122 
Made in DK

Power Output, 4 ohms:

2 x 40 watts

4 x 40 watts

Power Output, 2 ohms:

2 x 50 watts

4 x 50 watts

Power Output, Bridged 4 ohms:

120 watts

120 watts

Frequency Response:

20Hz ~ 20kHz +0dB, –1dB

20Hz ~ 20kHz +0dB, –1dB

Input Sensitivity:

250mV ~ 4V

250mV ~ 4V

THD + Noise (4 ohms):

0.05 %

0.05 %

Signal-to-Noise:

>100dB

>100dB

Maximum Current Draw:

18A

40A

Dimensions (w x h x l):

7-5/8" x 2-1/4" x 8-3/4" 

13-5/8" x 2-1/4" x 8-3/4" 

194 x 58 x 223mm 

347 x 58 x 223mm