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Appendix A
Most noise problems with the AudioControl EQX Equalizer/Crossover and EQL Equalizer can be
traced to improper level setting. The optimum signal level through the EQX or EQL is 1 volt. This
is considerably higher than the output of most head units. Both units have adjustable gain input
stages which boosts the input signal up to the 1 volt level. Since both units have bi-polar power
supplies, they can operate with 1 volt signals without sacrificing headroom. Remember that peak
output capability is directly related to power supply voltage. To be specific, the 9.5 volt maximum
output level of the EQX or EQL gives them 19.5 dB of headroom above 1 volt. On the other end of
things, the noise floor is 85.5 dB below 1 volt, giving a working signal-to-noise ratio of 85.5 dB.
Procedure for Head Units
1. Set the power amplifier to minimum sensitivity. This is the setting that produces the lowest
volume (but not off).
2. Set the level controls on the EQX or EQL to the 12 o’clock position.
3. Set the EQ IN/OUT switch to the OUT position (eq defeat).
4. Set any tone controls on the head unit to their “FLAT” positions.
5. Using an FM radio station or a tape, adjust the volume control on the head unit until you hear
audible distortion or reach 75% rotation. Be sure you have a good strong signal, or a cassette
recorded at a high level. Compact discs work very well.
6. If you hear distortion, verify that it is not the power amplifier clipping by reducing the input
level setting on the EQX or EQL. Of course, if the overall volume level isn’t very loud (actu-
ally quiet), you can probably bet that it isn’t the amplifier clipping.
7. If the volume control isn’t at 75% rotation and you hear distortion, reduce its setting slightly
until the distortion disappears.
8. Adjust the INPUT LEVEL controls on the EQX/EQL until the 3 dB HEADROOM INDICA-
TOR just blinks. Back the controls off slightly. Both channels should be set to the same setting.
If you can’t get the HEADROOM INDICATOR to blink, leave both controls at maximum.
9. Set the head unit’s volume control to minimum.
10. Set the power amplifier’s level controls for .8V (800 mV) to 1V (1000 mV) sensitivity. Usually
this is marked on the panel. If not, refer to the unit’s owner’s manual. Most currently available
autosound power amplifiers have sensitivity ranges from .2V to 1.5V. If this is true for yours,
then the proper setting (if it isn’t marked) would be around half rotation.
11. If you have an EQX and you are bi-amplifying then skip the remainder of this procedure and
pick up at the beginning of the special EQX procedure. If you have an EQX and are using
FULL RANGE output, then the remainder of this procedure applies to setting the level of the
EQX’s FULL RANGE output.
12. Advance the head unit’s volume control toward 75%. If the amplifiers clip, or if the system
gets too loud, you are done. If you reach 75% without the amplifiers reaching clipping, or if the
system isn’t loud enough (and the amplifiers aren’t clipping), increase the setting of the OUT-
PUT LEVEL adjustment on the EQL until the system is too loud, or you reach amplifier
clipping, whichever happens first.
13. Set the EQ IN/OUT switch to the IN position. Now that your levels are matched, you can
begin the equalization process.
Appendix A
(98 pages)
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