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Notes on EMC
Cables among the various pieces of equipment
should be arranged so that the loop they form
has the smallest possible area.
As a third tactic, the signal cables of all audio
equipment should be kept as far as possible
from sources of magnetic fields (transformers,
high-current power cables).
The "Ground Lift" switch will have no effect
if pin 1 of the microphone cable is connected
to its connector housing. In that case a ground
loop will be created via the shield contact of
the unit's input socket, since this contact is
connected to the chassis and thus to the AC
safety ground.
If hum problems occur, the best approach
is to reduce the extent of any ground loop.
Should this not help, any existing connection
between pin 1 and the plug connector hous-
ing of the microphone cable should be cut.
But please be aware that doing this can lead
to radio-frequency interference, especially if
the RF is not bypassed to the chassis by way
of a capacitor from pin 1 immediately at the
input.
A further possible cause of hum
Please note that strong hum can occur if the
input of the VSR 5 is left "open" (i.e. neither
a microphone nor any other item of equip-
ment is connected to it) while the Ground-Lift
switch is in the "LIFT" position. This hum does
not represent a defect, but results from the
fact that the circuit ground is not connected
to the chassis under these conditions, which
limits the ability of the chassis to act as a
shield even though it is connected to the AC
safety ground. The hum will disappear if any
of the following occurs:
a) if pin 1 of any cable connected to the VSR 5
is also connected to its connector housing;
b) if the VSR 5's Ground-Lift switch is set to
"Ground";
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c) if an item of equipment with a direct con-
nection between its circuit ground and its
AC safety ground is connected to the VSR 5;
or
d) double-insulated ("Class II") equipment
(
), if a cable with an extra ground wire
is connected.
11
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