V400 – Installation Guide
U-0398-0607.doc – Issue: 03 complete, approved
Page 12 of 24
8. Set the rear-panel EARTH LIFT switch to the DOWN ( , ON) ‘grounded’ position; see Figure 7.
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Set the EARTH LIFT switch to the UP ( , OFF) position to remove the mains earth from the
signal circuit if a +ve ground battery system is used, or it is necessary to avoid a ground loop
problem.
It is possible to form a ground loop when connecting pieces of audio equipment using unbalanced
connections that provide alternative earth connections via their cable screens. Such ground loops
result in audible ‘hum’ from the system.
Never disconnect the mains earth from the plug to attempt to cure a ground loop. In the event of
a fault, the equipment casing could become live.
The recommended method of wiring low-level signal interconnections to preserve EMC
(Electromagnetic Compatibility) performance and minimise the likelihood of ground loops is as
follows:
1) We always recommend screen to shell connection for best EMC performance, but break
the connection at the source end if a ground loop problem is encountered. In practice, the
connections between this equipment are balanced and short and it is unlikely that ground
loop problems will be encountered.
2) It is also possible to switch the rear panel EARTH LIFT switch to the UP ( , OFF)
‘ungrounded’ position. In some cases this may cure the problem.
Figure 7 Setting the Earth Lift switch
EARTH LIFT DOWN
9. Set the DIP switches at the rear of the mainframe as required; see Figure 8.
The internal DIP switches must be set before the last interface card (the one closest to the AC
mains socket) is fitted.
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