565E
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The two facts that you need to derive from this discussion are:
r Match signal levels for best headroom and signal-to-noise ratio.
r For audio, impedance matching is only needed for vintage equipment and power amplifier
outputs. In all other cases, ensure that your inputs bridge your outputs (meaning the
inputs are in the range of 2 to 200 times the output source impedance).
Signal Levels
The 565E is designed around studio/professional line levels: +4 dBu or 1.23 volts RMS. The unit is
quiet enough to operate at lower signal levels such as those found in semi-pro or musical instru-
ment (MI) equipment (-10 dBu or 300 millivolts).
I/O Impedances
The 565E is designed to interface into almost any recording studio or sound reinforcement applica-
tion. This includes:
r 600-ohm systems where input and output impedances are matched.
r Unbalanced semiprofessional equipment applications.
r Modern bridging systems where inputs bridge and outputs are low source impedances
(voltage transmission systems).
The 565E’s input impedance is greater than 20-kilohms balanced or 10K unbalanced. The inputs
may be driven from any source (balanced or unbalanced) capable of delivering at least -10 dBu into
the aforementioned impedances.
The 565E’s output impedance is 200 ohms balanced, 100 ohms unbalanced. The output line driver
delivers +22 dBm into 600-ohm balanced loads or +18 dBm into 600-ohm unbalanced loads.
Polarity Convention
The 565E inputs and outputs use the international standard polarity convention of pin 2 hot.
Therefore, if your system uses balanced inputs and outputs, and uses the 565E this way, then the
polarity convention is unimportant. If your system is both balanced and unbalanced, then you
must pay attention to this, especially when going in and coming out through different connector
types (like input on an XLR, output on a phone jack).
XLR 1/4" Phone Signal
Pin 1 Sleeve Ground
Pin 2 Tip High
Pin 3 Ring Low
Input and Output Connections
The illustration on the next page shows how to connect the 565E to balanced and unbalanced
sources and loads.
To operate the 565E from unbalanced sources, run a 2-conductor shielded cable (that’s two
conductors plus the shield) from the source to the 565E. 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 565E, 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 565E’s balanced input (even though the source is unbalanced). The other alternative
shown in the illustration converts the 565E’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.
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