Protection Indicator - NAD S200 Manuel D'installation

THE BENEFITS OF BALANCED CONNECTIONS
With a conventional (unbalanced) connection, audio signal current
flows from the preamplifier to the power amplifier via the cable's
centre conductor. To complete the circuit, audio signal current flows
back to the preamplifier ground via the cable's outer conductor. The
outer conductor also serves as the cable's shield.
When two audio components are connected together, power-supply
noise and "leakage" hum may also flow on the cable shields,
combining with the return audio current. The resulting distortion and
noise may depend on the orientation of AC power plugs in their
sockets. Designers of some audiophile cables combat this
contamination by leaving the shield unconnected at one end. Since
the shield is grounded at only one end, the performance of such a
cable may depend on the direction of its connection, i.e. whether the
shield is grounded at the preamplifier or at the power amplifier.
A three-wire balanced connection avoids all of these uncertainties.
The signal "hot" and return currents are both carried on inner
conductors. The separate cable shield, connected to the amplifier
chassis at both ends, protects the audio signal from all forms of
interference and power-supply noise. The advantage of this approach
is particularly evident with long connecting cables. Therefore, while
the S200 can provide excellent sound when used with any
preamplifier, the best (and most consistent) performance will be
obtained with a preamplifier that has balanced output wiring.
6. SOFT CLIPPING ON/OFF
When an amplifier is overdriven beyond its maximum power output
it normally produces "hard clipping" of the signal with harsh
distortion and power-supply buzz as the output transistors saturate.
The NAD Soft Clipping circuit gently limits the output waveform and
minimises audible distortion when the amplifier is overdriven. It
should be switched ON when playing music at very high levels that
might exceed the amplifier's power capacity. For convenience it may
be left ON at all times.
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7. BRIDGING ON (MONO) / OFF (STEREO)
This switch "bridges" the two channels together, forming a
monophonic amplifier with more than double the output power.
To convert to bridged operation, the following procedure should be
followed.
1. Switch Off the POWER.
NOTE: In the bridged mode the loudspeaker's impedance is effectively
halved as "seen" by the amplifier. An 8 ohm load looks like 4
ohms, a 4 ohm load looks like 2 ohms, and a pair of 4 ohm
speakers operated in parallel will resemble a 1 ohm load. Driving
paralleled low-impedance speakers to high levels will cause the
amplifier to overheat and shut down, or may cause internal fuses
to blow in order to protect the amplifier. In bridged mode you must
connect only ONE loudspeaker per channel whose nominal
impedance is 8 ohms or higher.
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2. Disconnect any signal cables from the input jacks. Decide whether
this amplifier will be driving the left or right speaker. Connect the
corresponding (left or right) signal cable from your preamplifier to
one of the L input jacks of this amplifier.
NOTE: In the bridged mode the amplifier is driven only through its L
(Left) input, even though it may be connected to the right speaker.
If another NAD S200 amplifier in bridged mode is used for the
second stereophonic channel, it also will be driven through its L
input, regardless of whether it is used to drive the left or right
loudspeaker.
3. Disconnect any wires from the speakers terminals. Select the wire
from the speaker that will be driven by this bridged amplifier.
Connect its "positive" conductor to the L+ terminal and its
"negative" conductor to the R+ terminal (i.e. the two red terminals).
Do NOT connect any wires to the black terminals (L- and R-).
CAUTION: In the bridged mode the speaker wires must be "floating"
with respect to the circuit ground. Do NOT connect the speaker
wires to anything that shares a common ground between stereo
channels (such as a speaker switch or an adapter for electrostatic
headphones), nor to anything which shares a common ground
with the amplifier's inputs (such as a switching comparator or a
distortion analyzer).
4. After the preceding conditions have been satisfied, move the
BRIDGING switch to ON (MONO). Finally turn the Power ON.
5. To return the amplifier to normal stereo operation at a later date,
first turn off the power. Re-set the BRIDGING switch to OFF
(STEREO). Restore normal left and right input connections, and re-
connect loudspeaker wires to the speaker terminals as described
above under SPEAKERS.
FRONT PANEL CONTROLS
1. POWER ON/OFF
Press the Power button to turn on the amplifier. The blue LED glows
when the power is on and the amplifier is ready for use. Press the
Power button again to switch the amplifier off.
2. POWER INDICATOR (STATUS)
This blue LED lights up when the S200 is switched on, and indicates
the operating status of the amplifier as follows.
DARK: Power off. The Power switch may be off, the AC Mains cable
may be unplugged or not connected to a live wall outlet, or the
internal fuse may have blown.
BLUE: Power on. The amplifier is ready for use.

3. PROTECTION INDICATOR

This blue LED lights up when the Protection mode is engaged,
meaning that the loudspeakers have been disconnected by an
internal relay. This mode is activated briefly during turn-on and turn-
off, to protect the speakers from low frequency thumps. At other
times the Protection mode may be activated by severe overheating,
short-circuited speaker wiring, or an internal fault.