Antex Electronics SX-5e - Manual (Page 19)

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Antex cards are “active”; transformers are not used. Normally,
one should not ground the output of an active driver. However the
drivers used on the Antex cards are specifically designed to do
this and behave identically to a transformer. The main difference
between grounding or not grounding the minus output is that
grounding the output will boost the output level by 6dB (double the
voltage level of the signal). This is not recommended when using
the trim setting of +20dB, as this will cause the output amplifier to
begin distorting before digital clipping is reached. The following
table shows what the output signal level will be at the point of
digital clipping for unbalanced output configurations.
Trim = +8 Trim = +20
Output Minus grounded +8 dBu Not recommended
Output Minus floating +2 dBu +14 dBu
IMPEDANCE AND SIGNAL LEVELS
The concept of matching impedances when connecting equip-
ment is important for radio frequency devices such as transmitters
and antennas, but does not apply to audio equipment in the same
way. What is important in audio equipment is minimum load im-
pedance. For example, the balanced output of an SX-36 has an
output impedance of about 100 ohms (50 ohms in each signal
leg), however, if you were to connect it to a 100 ohm load, severe
distortion would result. The output is designed for 600 ohm mini-
mum impedance, and a higher impedance, such as 10,000 ohms,
would work perfectly.
Matching signal levels is important to achieve optimum perform-
ance. Recording from a source with too high a signal level may
cause distortion, even if the level is adjusted in the Antex Mixer
application so that the VU meters show no clipping is occurring.