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14
You’re now ready to establish the correct gain structure—the key to getting the
best performance from the MPL 1502, or from any mixer, for that matter. This is
a simple procedure that ensures optimum input and output levels so that no
unnecessary noise (caused by too low a signal) or overload distortion (caused by
too high a signal) is created. Here’s a step-by-step description of how to do so:
a. With all connections made (as described above) but with
the power amplifier
and MPL 1502 off, start by setting the power amplifier volume to minimum. On
the MPL 1502, turn all channel gain controls fully counterclockwise (to their “-∞”
position), and then set the Main gain control to its “0” position.
b. Set all channel input trim knobs to their fully counterclockwise (+4) position.
c. Set all channel equalizer and pan/balance knobs as well as both Aux return
balance knobs to their center detent “0” positions.
d. Set all channel Aux send knobs and both Aux return level knobs to their fully
counterclockwise (“-∞”) position.
e. Turn on all devices connected to channel line inputs and Aux returns and set
their level controls to unity gain or, if there is no unity gain indicated on their out-
put control, to maximum. If you’ve got outboard effects processors connected to
Aux returns, make sure they are sending completely “wet” (processed) signal,
with no “dry” (unprocessed) signal mixed in.
f. If any condenser microphones are connected to the MPL 1502, turn on the
rear-panel Phantom switch.* Then turn on the MPL’s rear-panel Power switch—
the Power LED in the meter section will light up. Finally, turn on the power
amplifier.
g. Play an instrument connected to one of the MPL 1502’s line inputs** and,
while doing so, slowly raise the corresponding channel gain control to the center
detented “0” position—you should see the MPL meter begin to move. Now
carefully adjust the input trim control for that channel so that the “0” segment in
the meter lights frequently and the “+2” segment lights only occasionally. If the
incoming signal seems too hot even with the input channel trim all the way at its
minimum (+4) setting, you may need to lower the output level of the instrument,
though this will rarely occur. Conversely, if the signal is too low even with the
input channel trim all the way up, something’s definitely wrong: in all likelihood,
the connecting audio cable is faulty.
h. Once you’ve set the optimum level in step (g) above, continue playing the
instrument and slowly raise the power amplifier volume until you reach the level
you want to hear.
i. Repeat step (g) above for each instrument connected to the MPL 1502
channel line inputs.
* CAUTION: Before turning phantom power on, be sure to disconnect all non-
microphone signal sources (such as direct injection boxes) from the mic jacks.
** If you’re using an instrument such as electric guitar or bass, we recommend
that you connect it to the MPL 1502 with a direct injection box to ensure correct
impedance.
Setting the Correct Gain Structure