Protection, Faults And Warnings; Introduction; Safe Operating Area Detector (Soad); Very High Frequency Protection - Lab.gruppen C 88:4 Operation Manual

5. Operation and Performance

5.5 Protection, faults and warnings

5.5.1 Introduction

The C Series amplifiers incorporate a sophisticated and comprehensive set of protection features. Faults
and warnings are indicated on the front-panel and reported via the NomadLink network for indication on the
DeviceControl GUI.

5.5.2 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 operating area.
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.

5.5.3 Very High Frequency protection

All C Series amplifiers include protection circuits that detect continuous Very High Frequency (VHF) content
in the input signals. The detection begins at approximately 10 kHz and moves upwards to include ultrasonic
signals. If VHF signals are detected, the output will mute for 6 seconds before re-measuring. Once no continu-
ing 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 for
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 10 kHz and rising with a
-6 dB slope. This defines the VHF protection area. When continuous output power above the threshold line is
detected the VHF protection becomes active.
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C Series C 88:4, C 68:4, C 48:4, C 28:4 and C 16:4 Operation Manual rev 2.2.3
Output
power
20 Hz 10 kHz
Slow
Fast
20 Hz 10 kHz
Max. Peak
output power
VHF protection
operation area
- 6 dB slope
Max. Continous
output power
20 kHz 30 kHz
Attack time
VHF protection
20 kHz 30 kHz