THE BEAUTY OF POWER
B-52 US Series Professional Power Amplifiers - Instruction Manual
US SERIES AMPLIFIERS
the front and do not block the fans on the rear
panel. Make sure the open cell foam air filters
behind the vents on the front of the amplifier are
clean. If necessary, use a vacuum cleaner to
clean these air filters.
NOTe:
If the air filters become too dirty, the
amplifier may not operate normally as air
circulating inside the amplifier may become too
hot, thereby triggering the thermal protection.
To clean or replace air filters, first locate
plastic levers on front panel behind aluminum
handles. Pull out plastic frames holding air
filters. Carefully split plastic frames in two parts
and remove the filters. After cleaning filters, put
them back into plastic frames and install back to
the amplifiers. MAKE SURE TO CLEAN AIR
FILTERS PERIODICALLY TO ENSURE PROPER
OPERATION OF YOUR AMPLIFIERS.
Refer to the diagram on how to remove and
install the air filters.
TRANSFORMeR TheRMAl PROTeCTION:
If the
power transformer gets too hot, the thermal switch in-
side the transformer will trigger and will disconnect all
of the secondary power. When this occurs, there will
be no output signals coming from the amplifier and
all LEDs, including the PROTECT LED, will be OFF.
Once the transformer cools down, power to the ampli-
fier will automatically restore. In normal conditions,
the transformer will not overheat. Thermal protection
of the transformer indicates abnormal use, such as
excessive operation at a very low impedance at high
signal levels. In this case, check and reconfigure your
loudspeakers connection. Reducing the output level
can also help.
NOTe:
If the transformer overheats and
the thermal switch disconnects the power from
the amplifier, it will take some time for the trans
former to cool down before power is restored. It
takes much longer for the transformer to cool
down compared to overheated heatsinks.
ShORT CIRCUIT:
If the output is shorted because of
faulty wiring, the thermal circuitry will automatically
protect the amplifier and mute the output signals. If
this occurs, the load will disconnect. Check and cor-
rect the short wire condition.
dC VOlTAge PROTeCTION:
If an amplifier chan-
nel detects a DC voltage at the loudspeaker output,
the protection circuitry will trigger and the amplifier
will go into protection mode. In normal conditions
there should not be a significant DC signal on the am-
plifier outputs. DC on the outputs indicates a serious
problem with the amplifier. In this instance, the ampli-
fier must be referred to qualified service personnel.
SUBSONIC FReqUeNCy PROTeCTION:
Built-in
high-pass subsonic filters provide subsonic frequency
protection for each channel. This protection prevents
subsonic audio signals, which may sometimes be
present in the music program, from reaching your
loudspeakers. Limiting the subsonic frequencies in
the output signal improves the sound reproduction by
reducing the excursion of the transducer’s cone at low
frequencies and prevents excessive heating inside of
the amplifier.
NOTe:
US-Series amplifiers also employ
switchable high-pass filters (HPF), which limit the
low frequency range to 30/50Hz when
activated. Turn these HPFs ON and set them at
50Hz when connecting full range speakers to
the amplifier. This will improve the bass
performance of most full range speakers by
limiting uncontrolled and excessive cone motion
due to the lowest of frequencies. Using HPFs
with full range speakers provides more power to
the speaker’s rated range allowing higher SPLs.
Set the HPF at 30Hz when using the US-Series
amplifiers with quality subwoofers.
CURReNT lIMITINg PROTeCTION:
The output
stage of the amplifier is protected by current-limiting
circuitry. This circuitry is inactive under normal condi-
tions. It activates only when it senses a dangerously
high current through the output transistors, for exam-
ple when a connected load has an impedance that is
too low, or when the output of the amplifier is shorted.
Current limiting protection engages only when it is
needed and is not indicated on the front panel. If
there is a constant over-current condition it will acti-
vate the thermal protection. In this case, the PROTECT
LED on the front panel will illuminate.
ClIP lIMITeRS:
US-Series amplifiers have built-
in limiter circuitry for improved performance when
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