Crest Audio XRM - 12 - Manual (Page 27)

p. 27
Stereo Input channel
2
Rear panel features
+48 V On
+48 volts DC is applied equally (thru current-limiting resistors) to both pins 2 and 3 on both
the L & R mic-input XLR connectors.This feature is used with condenser microphones 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: See the Mono Channel Rear Panel description for warnings and limitations when operating
the phantom power switch.
Line Input jack
Line-level signals, balanced or unbalanced, may be brought into the input channel through these
1/4” TRS jacks.The LINE switch (front panel) must be pressed for this jack to be active. On the XRM,
the XLR jacks are normal'd to the switching contacts of these jacks. If nothing is plugged into the jack,
a padded XLR signal is available to the channel when the LINE switch is depressed.This allows the
LINE switch to perform a dual function: XLR pad if nothing is plugged into the Line jack, or
XLR(Mic)/Line input selection if the jack is being used.
Tip is Positive Input, Ring is Negative Input, Sleeve is Chassis Ground
Input impedance is 20K
Ω balanced.
XLR(Mic) Input jack
This balanced, latching, female XLR accepts a low-impedance microphone signal, or a line-level
signal, depending on the position of the LINE INPUT switch on the front panel.
Pin-2 is Positive Input, Pin-3 is Negative Input, Pin-1 is Chassis Ground
Input impedance is 4K
Ω balanced
Pin-1 Lift Switch
Pin-1 of all four of the XLR jacks is connected to the XRM chassis thru this switch.
This Pin-1 connection serves two main functions:
1) A shield connection point that allows interference signals (picked up by the cable shield) to be
effectively shunted to ground, thus avoiding signal degradation.
2) A DC return path for the +48 volt phantom power voltage.
Normally, this switch is left in the UP position; Pin-1 is tied to the XRM chassis, and the shielding and
phantom power functions are both maintained.When the XRM is used by itself, there is usually no
reason to press this switch.When the XRM is used in conjunction with another mixer, either by using
the built-in passive splitter, or when fed from an external splitter, there may be situations where
ground differences between mixers can cause a “ground-loop”.This usually manifests itself as a low-
freq hum (usually at the AC mains freq), a hi-freq buzz, or a combination of both. In most cases, lifting
the ground connection between mixers can clean up this interference.
Pin-1 of ALL XLR jacks is connected to Chassis ground.
Pin-1 of ALL XLR jacks is disconnected from Chassis ground.
NOTE 1: The pin-to-pin wiring between the paired XLR connectors is never changed by this switch,
it only disconnects the common, Pin-1 of the XLRs from the mixer chassis, never from one another.
NOTE 2: Remember- if this switch is depressed, it prevents the XRM phantom power from reaching
the attached microphones. Phantom power (if needed) must be supplied from an alternate source. an
alternate source.
Split-Out XLR jack
This male XLR jack is wired pin-to-pin to its corresponding female XLR input jack. In combina-
tion with the female XLR, it forms a passive,Y-Split of the input signal.This split-signal can be used to
feed the mic input to another mixer (usually the FOH mixer), or to “mult” the input to another chan-
nel on the XRM.
NOTE: This pin-to-pin connection between paired XLR jacks is NOT affected by the Pin-1 lift switch.