NAD S250, Owner'S Manual, Page: 5 / 32

REAR PANEL CONNECTIONS/CONTROLS
1. AC LINE CORD
Plug the AC line cord into a nearby wall outlet that provides the
correct AC power line voltage, as indicated on the back panel of the
unit. Do not plug the amplifier into a convenience outlet on your
preamp. The amplifier requires more power than these outlets
typically can provide.
2. INPUTS
Each of the five independent power amplifiers within the S250 has
its own signal input connector. Before making any connections to the
amplifier, make sure the POWER is switched OFF.
Connect the signal cables from the preamplifier, surround sound
decoder, or other signal source to these inputs. For optimum heat
dissipation in an AV surround system, we recommend you allocate
the audio channels to the inputs as follows:
Input 1 = Right Main speaker
Input 2 = Right surround speaker
Input 3 = Center speaker
Input 4 = Left Surround speaker
Input 5 = Left Main speaker
3. INPUT LEVEL CONTROLS
The amplifier is equipped with separate input level controls for each
channel. Before turning on the S250 for the first time, make sure all
level controls are in their normal full-clockwise position. With the
input levels set to the maximum position, the gain is exactly
conforming to THX Ultra™ standards.
Under some circumstances, other settings may be useful for:
• Level-matching - In systems that incorporate speakers of varying
efficiencies, it may be necessary to reduce the settings of some
controls to achieve proper channel-to-channel balance.
• Extended volume-control range - Many stereo systems have so
much voltage gain that the speakers (or your ears) are over-driven
at any volume-control setting higher than 11 or 12 o’clock
position of the volume control. As a result you can use only the
lower half of the volume control’s range, where adjustments are
imprecise and channel-balance errors tend to be greater. If all
input level controls are reduced, you can turn up your
preamplifier’s volume control, making effective use of most of its
range. (Suggestion: Adjust the input level controls so that your
preferred maximum sound levels occur at about 2 or 3 o’clock on
the volume control.) As an added benefit, this procedure
suppresses any noise produced by the preamp’s high-level circuitry
(e.g. any residual hum or hiss that does not go away when the
Volume is turned down).
4. SPEAKER CONNECTIONS
This amplifier is equipped with special high-current binding-post
speaker terminals. Connect the loudspeakers with heavy-duty (16-
gauge or thicker) braided wire. Connections may be made in any of
three ways. [See Figure 1.]
• Strip off a half-inch (1 cm) of insulation from each speaker wire.
In each conductor, twist the thin strands of wire together.
Unscrew the knob, insert the bare wire into the opening at the
base of the binding post, and tighten the knob until it grasps the
wire securely. Check to be sure that there are no loose strands of
wire touching the chassis or an adjacent terminal.
• Spade lugs. Unscrew the knob, insert the U-shaped spade lug
behind the bushing, and tighten the knob until the spade lug is
secured.
• Install banana plugs on your speaker wires, and plug them into
the end of each binding post. The terminals are separated by 3/4
inch (l9mm), so they will accept dual-banana plugs (this option is
not available on units with 230V line voltage factory setting).
NOTE: Speakers must operate in phase with each other in order to
produce a proper stereo image and to reinforce rather than cancel
each other’s output at low frequencies. When connecting speakers,
take care that the red (positive) terminal on each loudspeaker is
connected to the corresponding terminal marked red (positive) on
the amplifier.
5. AUTO TRIGGER ON/OFF
With the Auto Trigger switch set to the On position to activate the
12V-trigger. By connecting the 12V-trigger, the S250 can be remotely
switched to On and Stand-by and vice-versa. When set to the Off
position, the 12V-trigger input is not active.
NOTE: With the Auto Trigger switch set to the ON position and the
12V-trigger input connected, the S250 will switch from Off to Stand-
by when the Power Switch on the front panel is pressed. For normal
operation, ensure the switch is in the OFF position or that the 12V-
trigger input socket is not connected.
6. 12V-TRIGGER INPUT
For external Power on/Stand-by switching, connect the 12V-trigger
output of a source component to this DC input jack. The center pin
is the live or + connection, the outer sleeve of the input jack is the
12V-trigger - or ground connection.
NOTES: The S250’s 12V-trigger will work within a range of 6 to 15 V
DC level and typically draws less than 10mA of current. Check the
specifications of the 12V-trigger source to ensure it is compatible
with the S250’s 12V-trigger input. Do not exceed the recommended
voltage as this may cause damage to the S250.
If no cable is attached to the 12-trigger input socket on the S250’s
back-panel, the Power Switch will operate as normal, even if the
Auto Trigger switch on the back panel is in the ON position.
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