NAD Electronics S250 User Manual download pdf (Page 4)

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.

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NAD Electronics S250 User Manual Page 4

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