3.5. Input and Output Connections
Figure 3-1 illustrates how to connect the 425 to balanced and unbalanced sources and loads.
To operate the 425 from unbalanced sources, run a 2-conductor shielded cable (that's two
conductors plus the shield) from the source to the 425. At the source, connect the low/minus
side to the shield, these connect to the source's ground; connect the high/plus side to the
source's signal connection. At the 425, the high/plus wire connects to pin 2, the low/minus
wire connects to pin 3, and the shield (always) connects to pin 1. This is the preferred method
as it makes best use of the 425's balanced input (even though the source is unbalanced). The
other alternative shown in Figure 3-1 converts the 425's balanced input into an unbalanced
input at the input connector. This works, but is more susceptible to hum and buzz than the
preferred method. There is no level difference between either method.
You can drive unbalanced loads with the 425's outputs by using the XLR connector with pin 3
left open. In an emergency (the show must go on), you can ground pin 3, but if you have the
choice...leave it open. If you must ground pin 3, it is must be grounded at the 425, rather than
at the other end of the cable. The price, regardless of whether or not pin 3 is grounded is 6 dB
less output level. This can be easily made up via the output gain controls. If your system is
wired with pin 3 hot, pin 2 must float if you are driving an unbalanced load.
The 1/4-inch input jack is paralleled with the XLR-input and the screw terminals. In a large
installation, it is permissible to use one of the connectors as the input connection and to use
either or both of the remaining connections for paralleling other inputs with the 425.
The 1/4 inch output jack is a TRS (tip-ring-sleeve) jack wired for unbalanced operations. That
is, the tip is the signal connection, and the ring and sleeve connections both go to circuit
ground. This style of connection assures operation (passage of signal) regardless of the type of
plug inserted into the jack. The unbalanced output is always 6 dB lower in level than the
balanced output.
3-3
Rev 2.0, 10/29/93
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