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10 | JL Audio - HD900/5 Owner’s Manual
The output of the amplifier decreases for a
given input voltage when the “Input Range”
switch is placed in the “High” position. The
output increases with the switch in the “Low”
position. While this may sound counter-
intuitive, it is correct as described.
CHANNEL CONTROL SECTIONS
To the left of the “General Setup” section on
the Control Panel of the amplifer are three sets of
controls: one for the “Rear Channel Controls”
one for the “Front Channel Controls” and
one for the “Subwoofer Channel Controls”.
In each of these sections you will find a
rotary control labeled “Input Sens.” (Input
Sensitivity). These controls are designed to match
the input sensitivity of each channel section of
the HD900/5 to the specific signal source that
is feeding the amplifier. These controls must be
adjusted, with care, following the procedures
outlined in this manual. Failure to make correct
adjustments can result in weak output, excessive
distortion and/or undesirable noise in the audio
output of the amplifier!
Note: The Channel Control sections also house
“High-Filter” or “Low-Pass Filter” and “Filter
Freq.” controls. These are crossover filter controls
and will be discussed in the next section of this
manual. This section will explain the Input
Controls only.
“Input Sens.” Controls
Once the appropriate “Input Voltage” range
has been selected in the “General Setup” section
of the amplifier, the “Input Sens.” controls are
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 each pair of amplifier channels for maximum
clean output, please refer to Appendix C (pages
18, 19) in this manual.
After using this procedure, you can then adjust
the relative level of each channel pair by adjusting
the input sensitivity downward on any of the
channel sections, if they require attenuation to
achieve the desired system balance.
Do not increase the “Input Sens.” setting for
any amplifier or channel section in the system
beyond the maximum level established during
the procedure outlined in Appendix C (pages 18,
19). Doing so will result in audible distortion and
possible speaker damage.
Be aware that all three “Input Sens.”
adjustments will need to be made, regardless
of how many input cables are feeding the
amplifier. These controls will allow you to set
the appropriate relative levels for the “Front”
channels relative to the “Rear” channels and the
“Sub” channel (and any other amplifier channels
in the system).
CROSSOVER CONTROLS
Crossovers are groups of electronic filters
designed to control the frequency ranges
that each speaker in a system will be tasked
with reproducing. Proper crossover setup is
critical to sound quality and reliability.
The HD900/5 has three individually adjustable
filter controls, one for the “Front” channels,
one for the “Rear” channels and another for the
“Sub” channel. The “Front” and “Rear” filters are
high-pass filters (they attenuate low frequencies),