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Balanced Source Terminals (continued)
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XLR Connector - These are industry standard 3-pin connectors with a surrounding metal
shield. Pin 1 is always GND. Pin 3 is usually (+) and pin 2 is (-). Older equipment often
presents its outputs with pins 2 and 3 interchanged.
Unbalanced Source Terminals
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The signal outputs of equipment with unbalanced outputs consist of two terminals. The
positive (+) and the GND (or COMM or COM). The audio is applied across these terminals
as a voltage referenced to the GND terminal. There is no negative (-) terminal because it is
merged with the GND terminal.
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Unbalanced sources are less expensive to implement and are fine for situations where the
cable length needs to be short. If the interconnecting cable must be longer than 12 feet
(4 m), the source should have a balanced output. The reason is that unbalanced
connections are inherently more susceptible to the pickup of audio interference from AC
mains hum, RFI, and lighting dimmers.
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Typically, unbalanced sources have screw terminals, an RCA connector (also called a phono
connector), or a phone connector.
•
Screw Terminal - Each output of the source equipment has a positive (+) terminal and a
GND terminal. Connect the cable to these terminals. On some equipment, a chassis ground
screw or bolt may be found. Do not use this point as a signal ground.
•
RCA (phono) Connector - This connector accepts plugs with a center pin for the positive (+)
side of the signal, and a concentric shield for the GND side.
•
Phone Connector - This connector comes in several styles. Some are mono (tip and sleeve);
others are stereo (tip, ring, and sleeve). Some are 1/4 inch in diameter, some are 1/8 inch in
diameter. The sleeve of the connector is always used for GND. The tip of the mono plug
carries the positive (+) side of the signal. In stereo usage, the tip is the left channel positive
(+) signal and the ring is the right channel positive (+) signal.
GENERAL TROUBLESHOOTING TIPS
