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4.2.4 Avoidance of Ground-Loops
If for instance two audio components bearing a different grounding potential are connected, low-
frequency interference currents may superimpose a voltage drop on the audio signal. These dif-
fering ground potentials may stem from the individual earthing of each component. The interfer-
ence signal will appear with the magnitude of the difference between the grounding potentials.
While its typical frequency is located at the mains power frequency of 50 Hz the interference can
particularly occur in conjunction with the use of unbalanced input connections (such as Keyboard
6.3mm output jacks). Here, the interference signal is amplified together with the audio signal res-
ulting in disturbing audible hum. In general, balanced inputs have the ability to suppress interfer-
ence signals to a reasonable degree.
As a remedy, the ground-free switch (11) isolates the inputs grounding from chassis ground to
avoid ground loops.
If this measure should not bring relief it is advisable to insert DI-Boxes before the Inputs. In this
manner balanced interference signals should be cancelled to a reasonable extent.
4.2.5 Peak / limit indicator
The peak / limit indicator (labeled (26), located beneath the master volume control) displays the
status of the integrated protection circuits. The operating status is indicated by these displayed
colors:
Peak / Limit Indicator Status
green
orange
red
Status information meanings
Channel or / and amplifier peak (state indication: orange)
•
If orange color is displayed nearly constantly reduce the signal level or the volume settings
respectively. By this you prevent distorted amplification that may (under extreme circumstances)
cause damage to the unit. For loudspeaker protection the internal limiter will reduce the signal
level if the peak value is exceeded.
Over temperature / protection (state indication: red)
•
Being too strong driven the unit will mute the amplifier outputs until the power section (supply and
amplifier) have sufficiently cooled down to allow operation. Then, normal operation is resumed
automatically.
normal operation
channel or / and amplifier peak exceeded
over temperature / protection
12
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