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Balanced and Unbalanced Audio
Input Connection
The standard audio interface on American Fibertek products is a 600
Ohms balanced configuration. A balanced audio input is directly
connected across the plus and minus inputs. The shield or earth wire is
connected to the ground terminal. To connect an unbalanced signal to
the input, the audio signal is connected to the plus input. The shield
or ground wire is connected to both the minus and the ground terminals.
In either input configuration, the input impedance is 600 Ohms.
Output Connection
The output signal appears on both the plus and minus signal terminals.
Half of the signal appears on each output terminal. The two outputs are
180° out of phase. The balanced connection is made across both the plus
and the minus terminals. The balanced output impedance is 600 Ohms.
To connect unbalanced, the plus output is used for the audio
connection, along with the ground terminal. The signal level will be
half of the input (-6dB) in this configuration. The unbalanced output
impedance is 300 Ohms.
Signal Level
The ideal input level is 0dBm600. (This is 1mW across the 600 Ohm input
impedance.) On a voltage basis, this is equal to 0dBV or 2.19 Vp-p.
Higher input levels will cause increased distortion. Up to +3dBm, the
distortion will increase a small amount. Above this level the
distortion will increase rapidly as the signal is clipped. Lower input
signal levels will reduce the signal to noise ratio.
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