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symmetrical (balanced) sources (for instance a mixer) and symmetrical loads (for instance a power
amplifier (see figure). You can see that the TDcontroller provides a low impedance path between pin 1 of
its XLR connectors and its chassis. The TDcontroller can sustain high current in pin 1 without
degradation of output noise. We recommend that the sources and loads you use have the same
desirable characteristics.
It is sometimes claimed that connecting cable shield at both ends creates ground loops, and that the
current flowing in such loops will produce noise. This is not the case for most professional audio
equipment. In short, there are two kinds of loops in which voltages are present: the loops formed by
signal wires, and the loops formed by grounded conductors, among which are protective earth
conductors (PE) and signal cable shields.
When a cable shield is grounded at both ends, a loop is closed, and the resulting current causes a
reduction of the voltage induced on signal lines. This effect is what the cable shield is intended to
produce, since this is how it protects your signal from magnetic fields.
If
you
are
(unbalanced) source (not recommended),
it is best to use a shielded twisted pair and
to connect wire 3 of the cable to the shield
at the source output end (see figure). This
technique prevents noise currents flowing
on the return path of the signal. If you are
using an amplifier with an asymmetrical
(unbalanced) input, it is best to use a
shielded twisted pair, and to connect wire 3
at the TDcontroller end only, as shown in
Fig. 2. This keeps a good capacitance
balance for the signal, however noise
currents flow on the return path of the
signal. (Note that this is only acceptable for
a short cable).
If you are using a symmetrical (balanced) source or amplifier which is prone to become noisy when a
current of less than 100 mA at the mains frequency (50 Hz or 60 Hz) is sourced into pin 1 of its XLR
connectors, you might consider opening the ground loops.
NX242 USER MANUAL LOAD2_22
DATE : 12/3/2004
SETTING-UP ADVICE
using
an
asymmetrical
Mixing Desk
0V
Low Z ?
-
+
1
3
2
?
1
3
2
-
+
Low Z
Low Z
TDcontroller
IN
Amplifier
-
+
1
3
2
PE
Safety
PE
1
3
2
Ground
-
+
OUT
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