True to the Music
Radial Engineering Ltd. SW8 Owner’s Manual
9
FREQUENTLY ASKED QUESTIONS
Q: What testing procedures are recommended?
A: It will greatly depend on the system as a whole. The SW8 can be interfaced in several ways so the best recommendation is to devise
your own testing procedure that takes into account all the pieces of the system that will affect playback should one component
fail.
Q: Can I use the SW8 to switch other audio gear?
A: You can use the SW8 to switch any line-level audio application. One example would be switching between two eight bus consoles.
This would be advantageous when two FOH consoles are used, one for the warm-up act and one for the headliner. The SW8 can
be used to connect each console to the speaker management DSP processor or drive rack.
Q: Can I use the SW8 to switch one device between two inputs?
A: The SW uses a passive signal path from the ¼” and DB25 inputs to the DB25 direct output. Therefore these connectors can be used
to route audio signals in either direction. However, this does not apply to the front panel XLR outputs. The XLR jacks can only be
used as mic-level outputs because of the bridging transformers.
Q: Can the SW8 be used to switch a backup keyboard setup.
A: Yes. The SW8 would allow you quickly switch between main and backup keyboard systems. The SW8 could provide either a direct
output to a keyboard mixer or XLR mic-level outputs to an on-stage snake system, or both. Several SW8 switchers can be linked
to accommodate as many instrument inputs as needed.
Q: Can I overload the SW8?
A: The direct output can not be overloaded as it is a hard-wired connection through the switching relays. However, the transformer
isolated XLR outputs can be overloaded. The GLOBAL PAD feature is provided to prevent transformer saturation.
Q: Why doesn’t the SW8 have an OFF/ON switch?
A: Because the SW8 features a passive signal path, audio will always pass through even when the SW8 is de-energized. We
eliminated a power switch and added a power supply cable clamp to lower the risks of using the SW8 in a live performance.
Q: Why would I want to use the XLR outputs?
A: The XLR outputs are transformer isolated, which is the best way to eliminate buzz and hum caused by ground loops. You would
want to use the XLR outputs when connecting to a console that may pose a ground loop problem.
Q: What is a ground loop?
A: A ground loop is created when an audio system has multiple paths to ground, often called earth. This situation can occur when two
AC powered audio devices, such as two mixing consoles, are plugged into different power circuits and connected together via a
signal cable. Both audio devices have a path to ground through the third prong on the AC-mains cable. The signal cable completes
the loop by connecting the devices together through the signal cable’s shield (fi gure 1).
Once the loop is complete there is the electrical potential for DC voltage to fl ow through it. This potential is caused by the interaction
between devices with different ground voltage references and allows unwanted spurious current to fl ow through the shields of the
signal cables. This fl ow of DC voltage creates noise in the signal wires through induction and capacitance at the base frequency
of 50 or 60 Hz (hum) and the upper harmonics of 120 Hz, 240 Hz, etc. (buzz). Isolating or decoupling the audio signal with a
transformer at a point between the two devices is the best way to block the unwanted fl ow of ground-potential currents and
eliminate hum and buzz in audio systems (fi gure 2).
Earth
Earth
Ground Loop Path
Transformer Isolation
Figure 1 Figure 2
(16 pages)
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