NEXO A NALOGUE PSTD C ONTROLLERS Page 49/82degradation of output noise. We recommend that the sources and loads you use have the samedesirable characteristics.It is sometimes claimed that connecting cable shield at both ends creates ground loop, and that thecurrent flowing in such loop will produce noise. This is not the case for most professional audioequipment. In short, there are two kinds of loop in which voltages are present: the loop formed by signalwires, and the looS12 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 areduction of the voltage induced on signal lines. This effect is what the cable shield is intended toproduce, since this is how it protects your signal from magnetic fields.If you are using an asymmetrical (unbalanced) source, it is recommended to use a shielded twisted pairand to connect wire 3 of the cable to theshield at the source output end (see figure).This technique prevents noise currentsflowing on the return path of the signal. Ifyou are using an amplifier with anasymmetrical (unbalanced) input, it is best touse a shielded twisted pair, and to connectwire 3 at the TDcontroller end only, asshown in Fig. 2. This keep a goodcapacitance balance for the signal, howevernoise currents flow on the return path of thesignal. (Note that this is only acceptable for ashort cable).If you are using a symmetrical (balanced)source or amplifier which is prone to becomenoisy when a current of less than 100 mA atthe mains frequency (50 Hz or 60 Hz) issourced into pin 1 of its XLR connectors, you might consider opening the ground loop.8.4 Analogue TDcontroller USER GUIDELow Z1 23Low Z1 23TDcontrollerAmplifierMixing Desk1 23 1 23+-+-+-+-Low Z ?Low Z ?? PEPE SafetyGroundSHIELDSHIELD0VIN OUT
