JL Audio JD 400/4 Owner's Manual page 14

APPENDIX A:
Input Sensitivity Level Setting
Follow the steps below to adjust the input
sensitivity of each amplifier channel pair, simply
and easily, in just a few minutes to achieve overall
system balance.
Necessary Equipment
• Sine-wave test tone recorded at 0 dBfs reference
level in the frequency range to be amplified
for that set of channels (50 Hz for subwoofer
amplifier models or 1 kHz for a full range
amplifier models). Do not use attenuated test
tones (-10 dB, -20 dB, etc.).
Depending on your type of source unit, the sine-
wave may be played via a CD, USB thumb drive
or portable media player. Make sure to disable
any EQ/DSP modes on your portable media
player during level setting.
The Seven-Step Procedure
1) Disconnect the speaker(s) from the
amplifier's speaker output connectors.
2) Turn off all processing (bass/treble, loudness,
EQ, etc.) on the source unit, processors (if
used) and amplifier. Set the fader control to
center position and the subwoofer level control
to 3/4 of maximum, if used.
3) Set the "Input Voltage" switch to "Low". Turn
both "Input Sens." controls all the way down.
4) Set the source unit volume to 3/4 of full
volume. This will allow for reasonable gain
overlap with moderate clipping at full volume.
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5) Verify that you have disconnected the speakers
before proceeding. Play a track with the
appropriate sine wave (within the frequency
range to be amplified at 3/4 source unit volume.
6) Slowly increase the "Input Sens." control until
the LED "Clipping" trim ring is solidly lit,
indicating maximum, unclipped output. If the
LED "Clipping" trim ring is solidly lit with the
"Input Sens." control turned all the way down,
set the "Input Voltage" switch to the "High"
position, then slowly increase the "Input Sens."
control until its LED "Clipping" trim ring is
solidly lit. Perform this step for both "Input
Sens." controls.
7) Once you have adjusted the amplifier's input
sensitivity for each channel section to its
maximum, unclipped output level, reduce the
source unit's volume to prevent sudden output
bursts and reconnect the speaker(s). Play
music and adjust the "Input Sens." controls
downward if the amplifier requires attenuation
to achieve the desired system balance.
Do not increase any "Input Sens." setting for
any amplifier channel or channel pair in the
system beyond the maximum level established
during this procedure. Doing so will result in
audible distortion and possible speaker damage.
It will be necessary to re-adjust the "Input
Sens." if any equalizer boost is activated after
setting the amplifier's input sensitivity with this
procedure. This applies to any EQ boost circuit,
including source unit tone controls or EQ circuits.
EQ cuts will not require re-adjustment.
JL Audio