Crest Audio HPW - Manual (Page 14)

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p. 14
HPW TM owner’s manual
mono input 3
+48V - +48 volts DC is applied equally (through current-limiting resistors) to both pins 2
and 3 on the mic-input XLR connector. This feature is used with condenser micro-
phones and active direct boxes that require an external DC voltage (phantom power)
in order to operate.
For dynamic or ribbon mics, phantom voltage is not required and should be switched
OFF.
NOTE: Operating this switch (“ON” or “OFF”) causes large voltage swings to occur
at the input of the mic preamp. Care should be taken to insure that the channel is
muted, or the main faders are pulled down, to prevent a “pop” from reaching the audi-
ence.
pad - When engaged, the input signal is attenuated by 25dB to prevent strong signals
(from kick drums or lead vocals, for example) from overloading the preamp stage. The
pad is used to bring a hot mic-input signal down to a controllable level, or when a line-
level signal is present at the XLR input jack. This affects both the XLR and the 1/4”
inputs.
gain - The Input gain control range is closely related to the status of the PAD switch.
In order to establish proper gain structure in the console, input gain settings must be set
correctly, using the PFL switch and Solo system. The optimum gain setting will result in a
0dB level when checked using the PFL metering.
polarity (reverse) - This feature reverses the phase of the input signal and is used for
correcting or minimizing polarity and phase related errors. For example, occasionally a bal-
anced input connection is reverse-wired before it gets to the mixing console. This can hap-
pen in microphones, or in snake line interfaces. By using the polarity button, this type of
error can be corrected.
normal polarity (Pin 2 Hot) - switch “IN” position reverses polarity
lo-cut filter - This filter reduces or eliminates unwanted low frequencies without
substantially affecting the program material. Quite often, such unwanted low frequen-
cies are included with mic- or line-input signals. For example, stage rumble or wind can
be picked up through vocal mics. The cut-off frequency of the filter is 70 Hz and the
slope is -18dB per octave. This type of filter is also referred to as a Hi-pass filter (HPF).
It allows the hi-frequencies to pass, but it stops the lo-frequencies.
lo cut switch
When this button is depressed, Lo-Cut filter is on.
If the channel peak LED is
illuminated, first try lowering
the input gain control.
Only when this method is
unsuccessful should the pad switch
be engaged. +
When similar signals from
different channels are com-
bined, phase cancellations can occur.
Reversing the polarity of an input
signal can often minimize such
phasing errors.
+
The 48V switch should
not be engaged when using
standard (dynamic) microphones
or other sources that do not use
phantom power.
a
When performing outdoors,
wind-induced, low-frequency
rumble can get into the input
channels thru the microphones.
Engaging the Lo-Cut filter can
eliminate these power-stealing low
frequencies.
+
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3
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