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6 | JL Audio - M400/4 Owner’s Manual
7
INPUT SENSITIVITY CONTROLS
The controls labeled “Input Sens.” located in
each channel section can be used to match the
source unit’s output voltage to the input stage of
each pair of amplifier channels for maximum
clean output. Rotating the control clockwise will
result in higher sensitivity (louder for a given
input voltage). Rotating the control counter-
clockwise will result in lower sensitivity (quieter
for a given input voltage.)
To properly set the amplifier for maximum
clean output, please refer to Appendix A (page
14) in this manual. After using this procedure,
you can then adjust any or all “Input Sens.”
levels downward if this is required to achieve the
desired system balance.
Do not increase any “Input Sens.” setting for
any channel(s) of any amplifier in the system
beyond the maximum level established during
the procedure outlined in Appendix A (page 14).
Doing so will result in audible distortion and
possible speaker damage.
TURNON LEAD
The M400/4 uses a conventional +12V remote
turn-on lead, typically controlled by the source
unit's remote turn-on output. The amplifier will
turn on when +12V is present at its “Remote”
input and turn off when +12V is switched off. If
a source unit does not have a dedicated remote
turn-on output, the amplifier’s turn-on lead can
be connected to +12V via a switch that derives
power from an ignition-switched circuit.
The M400/4’s “Remote” turn-on connector is
designed to accept 18 AWG – 12 AWG wire. To
connect the remote turn-on wire to the amplifier,
first back out the set screw on the top of the
terminal block, using the supplied 2.5mm hex
wrench. Strip 1/2 inch (12mm) of wire and insert
the bare wire into the terminal block, seating it
firmly so that no bare wire is exposed. While
holding the wire in the terminal, tighten the set
screw firmly, taking care not to strip the head of
the screw and making sure that the wire (not the
insulation) is firmly gripped by the set screw.
INPUT SECTION
The M400/4’s input section allows you to send
signals to the amplifier section through the use
of two or four differential-balanced inputs.
Input connections are via up to two pairs of
traditional RCA-type jacks.
If you wish to send four discrete channels into
the M400/4, simply use all four inputs and set the
“Input Mode” switch in the “4 Ch.” position.
If you wish to use only two channels of
input to deliver signal to all four amplifier
channels, set the “Input Mode” switch to
“2 Ch.” and use only the inputs to channels
1 & 2. In this mode, Channel 3 will operate
with the Channel 1 signal and Channel 4
will operate with the Channel 2 signal.
Input Voltage Range:
The M400/4’s input sections are designed to
accept signal voltages from 100mV – 4V. This
will accommodate all preamp level signals and
many speaker level signals.
To use speaker-level sources, simply splice the
speaker output wires of the source unit onto a
pair of RCA plugs for each input pair. (or use JL
Audio part XD-CLRAIC2-SW) No “line output
converter” is needed in most cases.
If you find that the output cannot be reduced
sufficiently with a direct speaker level signal
applied to the amplifier, you may use a “line
output converter” to reduce the signal level.
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