True to the Music
®
Radial Engineering Ltd.
PowerPre 500 Module
Grounding
When you connect an AC powered device like a keyboard to the PowerPre, you can
occasionally run into noise problems known as ground loops. This is generally caused by
a confl ict between the electrical ground and the audio ground. The PowerPre solves the
problem by incorporating a ground lift switch that lifts the pin-1 audio ground at the XLR input.
You will need to pull the module out of the rack to change the ground switch setting.
AC POWER GROUND
GROUND LOOP PATH
AUDIO CABLE GROUND
LIFT
AC POWER GROUND
AUDIO CABLE GROUND
Important Note: INTERNAL GROUND LIFT AND PHANTOM POWER
There is a ground lift switch inside the PowerPre that is located at the back above the card-edge connector.
This switch lifts the pin-1 ground on the front panel XLR to help reduce hum and buzz caused by ground
loops. This is factory set in the grounded position (GND) so that phantom power will fl ow to condenser
mics. If your mic does not power up, check to make sure this is set
correctly. Because this special ground lift is only intended for use
when connecting electrically powered instruments, like keyboards,
the 48V phantom LED indicator will not be affected and therefore
may still illuminate if the ground is lifted. Under normal use, this
internal ground lift switch should be set to the “GND” position.
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