Cooling System; Protection Modes; Thermal Protection • Dc Protection - Lexicon LX - REV 3 User Manual

Basic Operation

COOLING SYSTEM

The LX Power Amplifiers use temperature-controlled fans to
exhaust heat. Heatsink temperatures are measured hundreds of
times each second. Under most conditions, the fans are set to a
slow speed. When the temperature climbs above 85˚C, the fans are
set to a medium speed. When the temperature climbs above
100˚C, the fans are set to a high speed.

PROTECTION MODES

The LX amplifiers are equipped to protect against overheating and
miswiring, as well as electrical failures such as short circuits, device
failures, internal faults, and DC output to the speakers. A
combination of dedicated circuitry and microprocessor control
ensures that the amplifier will perform safely and reliably under
extreme conditions.
THERMAL PROTECTION
JTS (Junction Temperature Simulation) provides an advanced level
of thermal protection that allows the LX amplifiers to achieve
maximum performance with a minimum number of output
transistors. This design requires a smaller quantity of high-quality
output transistors, enhancing performance and reliability.
JTS predicts the internal temperatures of output transistors to
prevent them from overheating. To arrive at an accurate internal
temperature prediction, JTS measures the output voltage and
current each output transistor delivers and combines this informa-
tion with heatsink temperatures. When an output transistor
reaches its maximum allowable temperature, it is instantly restrict-
ed until the temperature decreases.
2-8
JTS's dynamic nature enables it to avoid the problems inherent in
competing products that rely only on heatsink temperatures.
Heatsink temperatures do not always correlate to the temperatures
inside the output transistors. JTS is calibrated by device parameters,
which allow it to predict overheating even if the heatsinks are
relatively cool.
When JTS activates, a distorted signal will be present in the
corresponding channel. Check the airflow around the amplifier and
take the following measures:
• Provide additional cooling.
• Make sure speakers have adequate impedance ratings
(see page 2-5).
• Reduce system volume level.
In addition to the protection provided by JTS, the amplifier includes
thermal protection for each channel and the main power
transformer. If a heatsink temperature exceeds 115˚C, the channel
will deactivate and the corresponding channel status LED will flash
red. When the heatsink cools below 115˚C, the channel will
automatically reactivate and the corresponding channel status LED
will light blue.
If the main power transformer temperature exceeds 110˚C, the
transformer will deactivate, all channel status LEDs will no longer
be lit, and the standby LED will flash rapidly. The internal fans will
automatically be set to full speed to cool the transformer. Once the
transformer has cooled enough, it will automatically be reset and
the amplifier will operate normally. The channel status LEDs will
light blue, and the standby LED will no longer be lit.
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