Technology Brief Understanding Relationships Voltage-Current-Impedance

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Technology Brief: Designing for Great Performances
The primary protection circuits monitor for excesses in voltage,
current and temperature as shown in gure 9. Let’s review these
features.
High Temperature Protection
Ampliers convert power supply energy to load energy using
the output transistors, which are modulated by the input signal.
Output transistors generate heat that’s dissipated by the heat sink.
LAB GRUPPEN ampliers use a variable speed fan to exhaust the
heat through the chassis rear panel. That’s why it is imperative that
the air inlets on the front panel are kept clear of restrictions and the
lter screens are maintained.
At all times the heat sink temperature is monitored and the thermal
protection circuit will engage whenever the amplier exceeds
limits that would otherwise damage the output transistors. The
yellow TEMP LED on the front panel will ash when the amplier is
approaching the limit and once a thermal limit is exceeded the LED
will illuminate (steady) and the amplier channel will mute. When
a safe operating temperature is reached the amplier channel will
un-mute and return to service; the front panel TEMP LED will turn
off. Amplier thermal protection is inuenced by the selection of the
input gain and VPL. Input level should be reduced as soon as the
TEMP LED begins ashing. If the level reduction results in program
levels that are too low check the VPL DIP switches to ensure the
output is optimized for the load. If the VPL is set correctly and the
thermal protection circuit continues to engage you will need to
re-evaluate the load. This may necessitate a decrease in the number
of speakers connected thus changing the load impedance or it may
require an increase in the amplier size.
There’s also a separate thermal limit sensor for the power supply and
when triggered all channels will mute; they will remain muted until
the power supply returns to a safe operating temperature whereupon
the mute is released.
PAL Power Average Limiter
The C Series amplier’s power supply is monitored for current draw
that’s averaged. If a sustained high current situation occurs that’s
close to the trip point for the mains breaker, the PAL circuit will
engage to limit the draw and power output. The front panel PAL
LED will illuminate when active and the circuit does not affect short
duration, high current demands in the power supply that’s present
with dynamic program. A common reason for the PAL to engage with
a properly sized load is the presence of a short.
VHF Very High Frequency protection
Whenever the amplier is operating at near maximum power levels,
any very high frequencies that are caused by oscillations in the signal
chain will damage the speaker and/or the amplier. Sustained very
high frequencies above 10kHz are not typical in transient program
material and when sensed the channel will mute and the front
panel LED will illuminate. The circuit will automatically cycle every
6 seconds. Transient program materials with frequencies up to
20 kHz will pass without causing the circuit to engage.
Monitoring & Control
The NomadLink Network is a standard feature and enables remote
monitoring of the amplier conguration and condition. This is a very
useful tool when the ampliers are located in remote equipment
rooms that are away from the control position. A PC editor application
displays all front panel indicators along with the positions of the DIP
switches on the amplier rear panel. Additional remote control of
amplier functions includes individual channel mute or un-mute,
solo and sequential power on-off. Up to 16 subnet of 60 ampliers
each (Total = 3840 ch.’s) can be monitored and controlled in a
NomadLink network.
Conclusion
When laying out a sound system there are several design “Best
Practices” that should be observed to ensure the installed system has
the kind of performance and reliability you intended. A cornerstone of
these practices is a thorough understanding of Ohm’s Laws and how
it relates to equipment selections that properly match the application
- ampliers and their loads.
Once you have determined the correct size ampliers for your
system look at the various protection and monitoring features that are
available to you that enhance the sonic performance and reliability of
the system under all operation conditions. LAB GRUPPEN C Series
ampliers drive both low & high impedance systems and offer the
greatest utility for any permanent installation requiring exceptional
sound quality and performance.
Unique protection features such as VPL & CPL combined with a
broad assortment of input gain selections enable more options for
the designer to congure the headroom with maximum output.
LAB GRUPPEN’s power density, which is the measure of power
available in the smallest amount of rack space with 4 discreet
channels per C Series chassis means you’ll always have low & high
impedance conguration exibility, the most available power, best
sonic performance and most comprehensive speaker protection.
This adds up to the best overall value for any sound system amplier.