Technology Brief Protection Features Explained

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When it comes to causing problems, power ampliers are unique
inaudio systems. Whereas faults in other devices are usually
conned within the device itself, failures – or extreme abnormalities
– in a power amplier can have devastating secondary effects. In
some cases, costs for damage to connected loads can far exceed the
cost of the amplier.
In other, less dire circumstances, inadequate protection features
can cause short-term service interruptions due to muted outputs
or tripped mains breakers. Such temporary interruptions can prove
costly in terms of lost clientele or audience dissatisfaction.
To minimize any likelihood of either equipment damage or service
interruptions, C Series ampliers from LAB GRUPPEN are equipped
with the industry’s most comprehensive suite of protection,
monitoring, and fault warning features.
Current Protection Limiting (CPL) and Safe Operating Area
Detection (SOAD)
Technology: Current Peak Limiting (CPL) and Safe Operating Area
Detection (SOAD) are two related features that work in concert
to ensure that the amplier output stages always operate within
dened parameters, safeguarding the critical output transistors.
The SOAD circuits constantly monitor the outputs and compare
voltage against current to make sure the output transistors are
working inside their safe operating area. This sensing circuit works
in conjunction with the Current Peak Limiter (CPL), which applies
dynamic gain reduction only when the output devices draw current
outside their safe operating area. Activity of the CPL is indicated by
a ashing LED on the front panel, and by a CPL warning on the GUI
of NomadLink’s DeviceControl software. The CPL is non-adjustable:
xed thresholdvalues are determined by the model type, ranging
from 24.5 Arms on the C 68:4 to 8.5 Arms on the C 16:4.
Benefits: CPL and SOAD work together to prevent excessive output
current that could damage output transistors.
Voltage Peak Limiting (VPL)
Technology: Voltage Peak Limiting (VPL) keeps the amplier
working within its safe operating limits. In addition, VPL makes it
possible to scale the peak voltage in eight steps, adjusting the Voltage
clip level - and thereby the output power - to various connected
loads. This applies to both constant voltage systems (70 V and
100 V), as well as when output power needs to be adjusted to suit
a lower rated load. For constant voltage systems, setting the VPL is
simply a matter of selecting the voltage setting corresponding to the
system type. (The 141 V peak, for example, equates to 100 Vrms.)
For various low impedance loads, LAB GRUPPEN provides charts in
the C Series manual and on the LAB GRUPPEN web site that can be
used as guides for optimum setting of the VPL function. Also, a load
setting calculator is built into the DeviceControl software used with
LAB GRUPPEN’s NomadLink monitoring and control network.
Benefits: VPL keeps the amplier operating safely within it’s hardware
capabilities, as well as providing a smooth and well controlled output
signal even when the amplier is driven into clipping. VPL’s output
power management allows the same amplier to be congured for
use in several different applications. For example, in a smaller theater
or house of worship application, a single amplier could use one or
two output channels (separately or bridged) for the subwoofers, one
or two channels for the full-range FOH cluster, and the fourth channel
to drive a constant voltage system
Power Average Limiter
Technology: The Power Average Limiter (PAL) is a unique feature
that controls the ow of line current into the power supply. Power
consumption is limited to the amount that falls within the design
parameters of the power supply, ensuring that the PSU will never be
overloaded. Also, higher power models in the C Series can potentially
draw more current (with output devices still within safe operating
areas) than is allowed by the safety-mandated mains fuse. In this
case, the PAL limits average current draw to protect the mains fuse.
Benefits: PAL keeps current draw within operating limits to prolong
operational life of the PSU, and prevents blowing of the mains fuse
on higher power models.
Very High Frequency (VHF) Protection
Technology: C Series ampliers are designed to reproduce high
frequency audio signals nearly a full octave above those audible
to typical adult listeners. This high-end bandwidth contributes
to the renowned transparency and pristine transient response of
20 Hz 10 kHz 20 kHz
30 kHz
- 6 dB slope
VHF protection
operation area
Max. Peak
output power
Max. Continous
output power
Output
power
Attack time
VHF protection
Slow
Fast
20 Hz 10 kHz 20 kHz
30 kHz
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Technology Brief
Protection Features
C Series:
Installation-Dedicated Amplifiers