DAPAudio D2250, Manual

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Devices With Balanced
Balanced Portable Cable with Shield Intact
Inputs&Outputs
Grounp Lift Switch
Installed in Box or
on Rack Panel
Main AC Ground
Grounding on the Road
Many of the above procedures are difficult to use on the road .For example , the telescoping shield concept is
nearly impossible to use on a portable cable. Similarly , it is a difficult and time consuming process to search for
a water pipe ground every time the system is moved from one performance to another . Yet portable systems can
be extremely complex, and may have major grounding problems. The telescoping shield concept can be extended
to portable systems by installing a
“
ground lift switch
”
on the output of each device, and on the inputs of
devices after the mixer. Since microphones are not grounded except through the mixer, there is on need for an
input ground lift switch on most mixers. The diagram below shows a typical ground lift switch installation . By
judicious use of these switches , each piece of equipment can be AC grounded for safety without causing ground
loops.
Because of leakage currents from equipment in the audio system , and in the house, some noise currents can ride
on the AC ground wire and are able to enter the audio system. This problem is usually most noticeable with
sensitive equipment such as the mixer.Lifting the AC ground at the mixer can often solve this problem.However ,
lifting the AC ground on the mixer also lifts the AC ground on the microphone chassis , causing a safety hazard .
Try connecting the mixer and any other sensitive equipment to other AC circuits.The only other apparent solution
to this problem is to eliminate the noise on the AC ground, which is not an easy task.Since it has its own ground,
a portable AC power distribution system connected to the house service entrance may be the most effective way
to avoid all AC noises. Such a system can be designed and constructed by a qualified electrician ; check local
electrical codes before each use
.
USE OF GROUND LIFT SWITCH
Perhaps the best answer to portable system grounding problems, PFL,EMI, and AC noise ,is to develop a versatile
grounding scheme.Ground lift switches and adapters,and a portable AC power distribution system allow different
grounding techniques to be tried easily and quickly when a problem occurs.
8 BUS MIXING CONSOLE
31