Sub-18A
Manual del usuario /
User's manual
14
APPENDIX A. Line connections : un-balanced and balanced
There are two basic ways to transport an audio signal with microphone or line level:
Un-balanced line: Utilising a two-conductor cable, it transports the signal as the voltage between them. Electro-magnetic
interference can get added to the signal as undesired noise. Connectors that carry un-balanced signals have two pins, such as RCA
(
Phono) and ¼” (6.35 mm, often referred to as jack) mono. 3-pin connector such as XLR (Cannon) may also carry un-balanced signals
if one of the pins is unused.
Balanced line: Utilising a three-conductor cable, one of them acts as a shield against electro-magnetic noise and is the
ground conductor. The other two have the same voltage with respect to the ground conductor but with opposite signs. The noise that
cannot be rejected by the shield affects both signal conductors in the same way. At the device’s input the two signals get summed
with opposite sign, so that noise is cancelled out while the programme signal doubles in level. Most professional audio devices use
balanced inputs and outputs. Connectors that can carry balanced signal have three pins, such as XLR (
Cannon) and ¼” (6.35 mm)
stereo.
The graphs that follow show the recommended connection with different types of connectors to balanced processor or amplifier
inputs. The connectors on the left-hand side come from a signal source, and the ones on the right hand side go to the inputs of the
processor or amplifier. Note that on the un-balanced connectors on the left-hand side, two terminals are joined inside the connector. If
hum occurs with balanced to balanced connections, try disconnecting the sleeve (ground) on the input connector. Note that the
illustrations show what should be connected to what, but that pin locations on an actual XLR connector are different. Also, pin 2 hot is
assumed on XLR connectors.
