ART Pro Audio DPS II - Digital Preamplifier System - Manual (Page 12)

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Rear Input Jacks
The rear XLR and ¼” input jacks are directly wired together. The ¼” jack being
wired TRS balanced (Tip = HOT, Ring = COLD, Sleeve = GROUND). The rear
panel ¼” jack is intended for low level line inputs. The input impedance of these
jacks varies with the Input Impedance control from 150 to 3000 Ohms.
Use the front panel ¼” input for instruments and unbalanced line level signals.
If the front ¼” input is in use, the DPS II
 will use the instrument input and ignore
the rear panel inputs.
XLR Output Jacks (Rear)
The XLR Output jacks of the DPS II  are active balanced. You may use them in
an unbalanced configuration without harm to the output circuitry. The XLR
outputs can provide a hefty signal level (+28dBu) at a low impedance, so make
sure that you do not overdrive equipment with sensitive inputs. When using the
DPS II™ on the front end of a mixer, go into the mixer’s line in or insert inputs
and not necessarily into the mixer’s microphone input, unless the mixer can pad
that input’s level.
¼” Output Jacks (Rear)
The ¼” Output jacks are unbalanced and should be used for sending signals to
amps, processors, or other unbalanced configurations.
Both balanced and unbalanced output connections may be used simultaneously.
This is particularly useful when using the DPS II
 as a direct box for instruments
or line level signals. Make sure that both pieces of equipment connected to the
preamp’s outputs are connected to the same earth ground, beforehand, to avoid
electrical shock.
If you experience a grounding hum when using both output connectors (one to a
console, one to an instrument amp) simultaneously, a ground loop may be the
problem. To remedy this problem, disconnect the ground wire (pin 1) from the
XLR cable plugged into the preamp’s output. This interrupts the ground path, and
therefore breaks the loop.