NAD S250, Owner'S Manual, Page: 4 / 32

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NAD S250 Five Channel Power Amplifier
ABOUT THE S250
Designed specifically for home theater and custom installation set-
ups, the NAD S250 Power Amplifier delivers uncompromising
performance. It combines supreme reliability, flexibility, and
performance with outstanding value. Flexibility has always been an
important part of NAD components. Such flexibility is particularly
important in home theater and other multi-channel systems. That’s
because it is common for a multi-channel system to incorporate
different brands and models of loudspeakers. Often these speakers
have different levels of efficiency. The individual input level controls
for the five channels of the NAD S250 make it easy to compensate
for such differences in efficiency, and achieve the ideal system
balance. Ample dynamic headroom of the S250 ensures that the very
wide dynamic range of modern cinema soundtracks and digital
music sources will be preserved. In addition, the S250 will handle low
impedance speakers with ease.
The S250 incorporates NAD’s unique Soft-Clipping circuitry in all five
channels. Any amplifier can be overdriven if it is played too loud,
exceeding the maximum output power. Under such circumstances,
amplifiers produce extreme high levels of distortion which, besides
sounding very unpleasant, can damage your loudspeakers. The Soft
Clipping circuit suppresses such distortion and minimizes the risk of
damage to speakers. This is particularly important with movie
soundtracks which often contain very dynamic outbursts in which,
unlike music, it is difficult to hear this potentially damaging
distortion. The Soft Clipping LED on the front panel illuminates when
the Soft Clipping circuit is engaged. Soft Clipping can be defeated
with a rear panel switch.
The 12V trigger connection on the back panel allows the amplifier to
be switched from On to Stand-by and vice-versa remotely. This way,
the S250 can be part of a system which can be turned on and off
with a single command, easing operation. The 12V trigger also
allows the amplifier to be installed in places not in easy reach.
THE DESIGN
The NAD S250 houses five individual amplifiers, each on separate
circuit board. Each amplifier channel acts as a “mono block” within
the chassis. Each input connector, and set of loudspeaker output
terminals, is directly connected to that channel’s circuit board. This
design eliminates extra wiring and keeps signal paths short.
Furthermore, this modular design increases reliability and thermal
efficiency. The input circuit uses a totally new dual differential input
topology that operates in true Class-A mode. The special
Holmgren™ toroidal transformer has less hum and magnetic leakage
than conventional toroidal transformers, but retains the usual
benefits of high efficiency and high power-to-weight ratio.
Ruggedness and reliability are critical in custom-installed systems. The
S250 uses a combination of fuses and non-intrusive electronic
protection. This provides highly effective protection that does not
effect audio performance. Each channel is protected against excess
temperature, DC fault and loudspeaker short-circuit. The S250’s
inherently conservative, high-voltage/high-current output stage has
been designed for years of trouble-free service.
NAD was the first company to introduce a THX certified power
amplifier. In that tradition, the S250 easily passes Lucas Films’
stringent THX performance requirements. As a result the NAD S250
will handle the most demanding signals with ease, and yet preserve
every subtle audio detail in the most demanding THX and Dolby
Surround systems.
INSTALLATION PRECAUTIONS
WARNING - To reduce the risk of fire or electrical shock, do not
expose the amplifier to rain or moisture.
CAUTION - For units factory-set at 115 volts AC match the wide
blade of the power plug to the wide slot of the power outlet, to
prevent electrical shock. Be sure the plug is completely inserted into
the receptacle.
Turn off all the components in the system whenever connecting or
disconnecting any audio signal wiring. Once all signal connections
have been completed, turn down all the system’s main volume control
before turning the system components on. Then increase the volume
control setting carefully to avoid damage to the system components.
NOTES ON INSTALLATION LOCATION
Read and follow all the safety instructions on the first page of this
manual. To prevent a fire or shock hazard, do not place the amplifier
where it will be exposed to any water or moisture. If liquid
accidentally gets into the amplifier, immediately unplug the AC
power cord. Do not operate the amplifier again until it has been
examined by a service technician.
The amplifier generates a moderate amount of heat, requiring
ventilation. Do not obstruct the air outlet grilles on the top or
bottom covers. There should be at least 3 inches (7.5 cm) of
clearance above the amplifier and 1 inch (2.5 cm) to the sides. Do
not place the amplifier in an enclosed area, such as in a bookcase or
in a cabinet, unless it is very well ventilated. Be sure there is
adequate room behind the amplifier for signal input and speaker
output connections. If you want to locate the amplifier on a carpeted
floor, place a board under it in order to prevent it from sinking into
the carpet, blocking the air inlets on the bottom. Do not place the
amplifier where it will be exposed to direct sun light for prolonged
periods of time.
This unit may be installed on any sturdy, level surface.
NOTE: The amplifier’s weight must always rest on its bottom feet.
Never put the amp down on its rear panel, with its front panel facing
up. Doing so risks damage to the input/output connectors.
The power transformer in the S250 generates a magnetic hum field
of moderate strength. Turntables (especially those with a moving-coil
pickup cartridge) should not be located near the amplifier. Magnetic
media, such as audio or video tapes and computer diskettes, should
not be stored near the amplifier.