User Manual

Radial Engineering Ltd. J48 Stereo™ User Guide
5
GROUND LOOPS
A common problem occurs when connecting a stage amp to the direct box whereby a so called ground loop can present
itself. This is often caused by DC offsets or voltage differentials that can introduce hum and buzz in the sound system. The
rst line of defence is to lift the audio ground - pin-1 on the XLR. With most direct boxes, when you lift the ground you also
disconnect phantom power. This then requires using a battery or external supply to provide the power – options that are
not desirable. With the J48’s unique circuit design, instead of lifting the ground at the XLR, it is done in the power supply
section of the circuit board. This eliminates the noise problem without losing power. If you hear noise, simply depress the
ground lift switch.
60Hz
Hum
GROUND LOOP HUM
TRANSFORMER
BREAKS THE LOOP
ELECTRICAL GROUND PATH
EMI & RADIO NOISE
SOURCE
RECEIVE
The image above shows an audio source and a destination with a common electrical ground. As the audio also has a ground, these
combine to create a ground loop. The transformer and ground lift work together to eliminate the ground loop and potential noise.