Symetrix 572 SPL, Руководство пользователя

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The two facts that you need to derive from this discussion are:
1. Match signal levels for best headroom and signal-to-noise ratio.
2. For audio, impedance matching is only needed for antique equipment and power amplifier
outputs. In all other cases, ensure that your inputs bridge (are in the range of 2 to 200 times the
output source impedance) your outputs.
Signal Levels
The 572 is designed around studio/professional line levels: +4 dBu or 1.23 volts. The unit is quiet
enough to operate at lower signal levels such as those found in semipro or musical-instrument (MI)
equipment (-10 dBV or 316 millivolts).
I/O Impedances
The 572 is designed to interface into almost any sound reinforcement application or background/
foreground music application. This includes:
1. 600-ohm systems where input and output impedances are matched.
2. Unbalanced semiprofessional equipment applications.
3. Modern bridging systems where inputs are bridged and outputs are low source impedances
(voltage transmission systems).
The 572’s line input impedance is greater than 40k Ohms balanced, and greater than 40k Ohms
unbalanced. The inputs may be driven from any source (balanced or unbalanced) capable of
delivering at least -10 dBV into the aforementioned impedances.
XLR Polarity Convention
The 572 uses the international standard polarity convention of pin 2 hot. The following chart shows the
connections for each type of connector:
Input and Output Connections
Appendix B illustrates how to connect the 572 to various balanced and unbalanced sources.
To operate the 572’s balanced line inputs from unbalanced sources, run a 2-conductor shielded cable
(that’s two conductors plus the shield) from the source to the 572. 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 572, the high/plus wire connects to the screw terminal marked with a “+”, the
low/minus wire connects to the screw terminal marked with a “—”, and the shield (always) connects to
screw terminal marked G
ND
. This is preferred as it makes best use of the 572’s balanced input (even
though the source is unbalanced). The other alternative shown in Appendix B converts the 572’s
balanced input into an unbalanced input at the 572’s input terminals. This works, but is more suscep-
tible to hum and buzz than the preferred method. There is no level difference either way.
We do not recommend unbalancing the 572’s microphone inputs. Doing so makes these inputs
considerably more susceptible to hum and induced noise.
XLR Tip-Ring-Sleeve Signal
1 Sleeve Ground
2 Tip High
3 Ring Low