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| JL Audio - MHD600/4 Owner’s Manual
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“status” led / ProteCtion CirCuitrY
There is a single multi-color LED on the
control panel of the amplifier to indicate the
amplifier’s operating status. This LED’s behavior
is as follows:
1) Flashing Green: amplifier is powering up,
audio output is muted.
2) Constant Green: amplifier is on and
functioning normally, audio output is active.
3) Constant Red: lights to indicate that the
amplifier has exceeded its safe operating
temperature, putting the amplifier into a
self-protection mode, which reduces the
peak power output of the amplifier. The red
light will turn green and the amplifier will
return to full-power operating mode when its
temperature returns to a safe level.
3) Constant Amber (yellow): lights to indicate
that the impedance of the speaker load
connected to the amplifier is lower than
the optimum load impedance range for the
amplifier. When this light is on, a protection
circuit engages and reduces the power output
of the “Front” or the “Rear” channels,
depending on which channel is experiencing
the problem. The amber indicator will also
light when a short-circuit is detected in the
speaker wiring (this can be a short between the
positive and negative speaker wires or between
either speaker wire and the vessel chassis). This
can be used to diagnose a short-circuit by only
connecting one of the amplifier sections at a
time (“Front” or “Rear” channels). The amber
LED will light when you connect the section
that is experiencing the problem and turn the
volume up.
4) Alternating Red and Green: lights to indicate
that the amplifier is experiencing a fault
that may require service of the amplifier, its
wiring or the vehicle’s charging system. Audio
is muted when this fault occurs. The most
likely cause of this fault is a low supply voltage
condition. If battery voltage drops below 8.5
volts at any point, the amplifier (except for the
“Status” LED) will shut itself off to protect itself
and the vehicle’s charging system. If the voltage
drops below 6 volts, the “Status” LED will also
turn off.
The amplifier will turn back on automatically
when voltage climbs back above 9 volts. This
shut-down and turn-on behavior may happen
in a rapid cycle when bass-heavy program
material causes a weak charging system to
momentarily dip too low. If this is happening
in your system, have your charging system
inspected to make sure it is working properly.
If no problem is found with the supply
voltage to the amplifier and you are
still seeing alternating Red and Green
on the “Status” LED, it is likely that the
amplifier is suffering from an internal
fault that requires factory service.
For more information on troubleshooting this
amplifier, refer to Appendix D (pages 20, 21).
serViCing Your Jl audio amPliFier
If your amplifier fails or malfunctions, please
return it to your authorized JL Audio dealer so
that it may be sent in to JL Audio for service.
There are no user serviceable parts or fuses inside
the amplifier. The unique nature of the circuitry
in the JL Audio amplifiers requires specifically
trained service personnel. Do not attempt
to service the amplifier yourself or through
unauthorized repair facilities. This will not only
void the warranty, but may result in the creation
of more problems within the amplifier.
If you have any questions about the installation or
setup of the amplifier not covered in this manual,
please contact your dealer or technical support.
Jl audio technical support:
(954) 443-1100
9:00 AM – 5:30 PM (Eastern Time Zone)
Monday - Friday
aPPendix a:
mHd600/4 specifications
Amplifier Topology:
Class D, switching type with
patented Single-Cycle Control™ technology.
Power Supply:
Pulse width modulation-regulated
switching power supply
Recommended Fuse Value / Type:
50A (AFS, AGU or
MaxiFuse™)
Rated Power (Stereo):
150W RMS x 4 @ 1.5-4Ω (11V - 14.5V)
Rated Power (Bridged):
300W RMS x 2 @ 3-8Ω (11V - 14.5V)
THD at Rated Power:
<0.03% @ 4Ω per channel
(Average at 1 kHz)
Signal to Noise Ratio (20 kHz Bandwidth):
Referred to Rated Power: 110 dBA
Referred to 1 Watt: 88.2 dBA
Frequency Response:
6 Hz - 30 kHz (+0, -1dB)
Damping Factor:
300 @ 4Ω per ch. / 50 Hz
150 @ 2Ω per ch. / 50 Hz
Crossover Filters:
Filter Sets:
Two (Front Channel and Rear Channel)
Filter Type:
State-variable, 12 dB/octave Butterworth or
24 dB/octave Linkwitz-Riley
Filter Modes:
Low-Pass or High-Pass, Defeatable.
Cutoff Freq. Range:
Continuously variable, 50 - 500 Hz
input sections:
No. of Inputs:
Two Stereo Pairs (Front and Rear)
Input Type:
Differential-balanced with RCA jack inputs
Input Range:
Switchable from 200mV - 2V RMS (Low)
to 800mV - 8V RMS (High)
Preamp output:
2-Channel, buffered pass-through type, switch-selectable
to pass signal from “Front” inputs only, or from all four
inputs (summed).
Chassis dimensions (lxwxH):
10.74 in. x 7.85 in. x 1.93 in. (273 mm x 199.5 mm x 49 mm)
Dimensions do not include connectors.
Due to ongoing product development, all specifications are subject to
change without notice.
