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12 | JL Audio - MHD750/1 Owner’s Manual
13
REMOTE LEVEL CONTROL OPTIONAL
With the addition of the optional Remote Level
Control (HD-RLC), you can control the volume of
the MHD750/1 from the front of the vessel. This
is particularly useful for subwoofer level control.
The HD-RLC connects to the jack labeled
“Remote Level Control” on the Connection
Panel of the amplifier using a standard telephone
cable (supplied with the HD-RLC).
If desired, multiple MHD amplifiers can be
controlled from a single HD-RLC controller
using a simple phone line “splitter” and multiple
phone cables (not supplied).
Remote
Level
Control
Inputs
L
R
L
R
+12 VDC Ground Remote
Preouts
+12 VDC Ground Remote
When connected to the amplifier, the HD-RLC
operates as follows. At full counter-clockwise
rotation, the audio will mute completely. At full
clockwise rotation the level will be the same as if
the HD-RLC was not connected at all. In other
words, it operates strictly as a level attenuator.
The RBC-1 Remote Bass Control used with
JL Audio Slash, Slash v2, e-Series, A-Series and
G-Series amplifiers is NOT compatible with the
MHD Series amplifiers. If you attempt to
connect an RBC-1 to an MHD amplifer, the
control will not work. You must use the
HD-RLC controller.
SPEAKER CONNECTIONS
The MHD750/1 employs JL Audio’s exclusive
Regulated, Intelligent Power Supply (R.I.P.S.)
design. This sophisticated power supply allows
the amplifier to produce its optimum power (750
watts x 1) over a wide range of supply voltage and
speaker impedances.
Remote
Level
Control
Inputs
L
R
L
R
+12 VDC Ground Remote
Preouts
+12 VDC Ground Remote
Unlike conventional amplifiers that require
a specific impedance to produce optimum
power, the R.I.P.S.-equipped MHD750/1 gives
you the freedom to use a variety of speaker
configurations that achieve final nominal
impedances between 1.5 – 4Ω (without
sacrificing power output or sound quality).
The operation of the R.I.P.S. circuitry is
entirely automatic and adjusts itself every time the
amplifier is turned on. There are no user controls
to configure. The system operates through
multiple stages of impedance optimization,
choosing the stage most appropriate to the actual
impedance of the speakers you connect to it.
If you connect a load higher than 4Ω nominal,
power will drop by half with every doubling of
impedance above 4Ω stereo. If you connect a
load lower than 1.5Ω nominal, the amplifier
protection circuitry activates a “safe” mode
which reduces amplifier power to protect the
circuitry from failure (the LED status indicator
on the control panel will light up amber to
indicate that this has happened). See page 14
for details.
OUTPUT POLARITY CONTROL
Depending on the distance relationship of
the mid-bass speakers and the subwoofers in a
system, it can be desirable to reverse the polarity
of the subwoofer system in order to produce
a better transition between subwoofer and
midbass speaker output. This is normally done
by swapping the positive and negative wires
connected to the subwoofer(s).
The “Output Polarity” switch on the MHD
750/1 allows you to quickly peform this polarity
inversion without touching any wires. Simply
flip the switch from the “0” (normal) to the “180
deg.” (reversed) position.
Neither switch position is “correct” for every
system. Experiment to determine which polarity
produces the best overall bass performance
in your system, listening in particular to the
mid-bass smoothness and impact to make your
determination. If you change crossover slopes
or crossover filter frequencies, you may need to
revisit this control as these can affect the phase of
the speaker systems in the overlap region.
PREAMP OUTPUTS
The MHD750/1 incorporates a pass-through
preamp output section, so that additional
amplifiers can easily be connected to the same
signal(s) feeding the MHD750/1. These preamp
output signals are accessible via a stereo pair
of RCA-type jacks, labeled “Preouts”, on the
Connection Panel.
Remote
Level
Control
Inputs
L
R
L
R
+12 VDC Ground Remote
Preouts
+12 VDC Ground Remote
The term “pass-through” refers to the fact that
the Preamp Output signals are not affected by
any crossover filter or input sensitivity setting
selected on the MHD750/1 (if the input signal
is full-range, the Preamp Output will be full-
range). These preamp output signals are buffered
to prevent noise and are always preamp level,
regardless of the level of signals feeding the
MHD750/1’s inputs.
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