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7.5 Protection, faults and warnings
7.5.1 Introduction
The 10K4 amplifier incorporates a sophisticated and
comprehensive set of protection features. Faults and
warnings are indicated on the front panel and
reported.
7.5.2 Safe Operating Area Detector (SOAD)
The Safe Operating Area Detector (SOAD) compares
output voltage against output current to ensure that
the output transistors are working inside their safe.
The SOAD provides fault monitoring and input to the
Current Peak Limiter (CPL). The SOAD has no
dedicated indicator, and its operation is revealed
only in conjunction with features such as the CPL.
7.5.3 Very High Frequency (VHF) protection
The 10K4 amplifier includes protection circuits that
detect continuous Very High Frequency content in
the input signal. The detection begins at
approximately 10KHz and moves upwards to include
ultrasonic signals If VHF signals are detected, output
will mute for 6 seconds before re-measuring. Once
no continuing VHF signal is detected, the output un-
mutes and returns to normal operation.
This feature recognizes that continuous full-scale
VHF signals do not appear in natural, sources such
as music. Any such signals can therefore be
considered as a fault when present. VHF protection
is essential in avoiding damage to high frequency
drivers.
The VHF protection operational area is dependent on
output power level and frequency. The illustration
below shows a decreasing threshold on the output
power level, starting at approximately 10KHz and
rising with a -6dB slope. This defines the VHF
protection area. When continuous output power
above the threshold line is detected the VHF
protection becomes active.
The Attack time for the VHF protection is increasingly
shorter at higher frequencies. For example, an
ultrasonic continuous signal will cause the outputs
to mute rapidly, where it will take several
milliseconds for a 10KHz continuous signal to trigger
the output mute. This is shown in the illustration
above.
The VHF protection is NOT a limiter and does not
alter the amplifier's frequency response.it is
implemented solely to detect continuous VHF
content. The amplifier will always pass VHF peaks at
full power, with no effect on musical transients
The VHF protection is indicated by a red LED on the
amplifier front panel, with output muting for 6
seconds when in action.
If you bench test the amplifier using a
continuous, full-scale sine wave input above
10KHz, the VHF protection will activate and
prevent measurement of full peak output
power. (Output will be muted long before
maximum output power is attained.) To
measure the true peak output power, use a
burst signal.
7.5.4 DC protection
DC protection is implemented on each output to
prevent damage to connected loudspeakers. DC
present at the output will trigger muting and
illuminate the fault LED indicator. Any DC present at
the output indicates a hardware malfunction that
requires servicing of the amplifier.
Zenith 10K4 Amplifier Manual
21
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