NAD 2155 - Installation Notes; A Note on Installation; Rear Panel Connections; Input Jacks

ENGLISH
A NOTE ON INSTALLATION
This unit may be installed on any sturdy, level surface.
Since its power transformer generates a magnetic hum field
of moderate strength, a turntable (especially one with a
moving-coil pickup cartridge) should not be located directly
to the left of the amplifier nor directly above it.
The amplifier generates a modest amount of heat and
thus requires some ventilation. Do not place it on a rug or
other soft surface that it could sink into, obstructing the air
inlets on its bottom. And be careful not to obstruct the air
outlet grille on the top cover.
CAUTION: To prevent a fire or shock hazard, do not
permit liquid or moisture to enter the amplifier. If liquid is
accidentally spilled on it, immediately shut off its power and
unplug its AC power cord. Allow sufficient time for complete
evaporation to occur before operating the amplifier again. (If
the liquid is anything but water and/or alcohol, the amplifier
should be examined by-a service technician before power is
applied to it.)
Do not open the amplifier, or attempt to modify or repair
it yourself. Refer all servicing to a qualified technician.
The lightning flash with arrowhead, within an equilateral
triangle, is intended to alert the user of the presence of
uninsulated “dangerous voltage” within the product’s encio-
sure; that may be of sufficient magnitude to constitute a
risk of electric shock to persons.
REAR PANEL CONNECTIONS
1. INPUT JACKS
Connect the signal cable from your preamplifier to these
jacks. In normal stereo operation the lower jack is for the
right-channel signal and the upper jack is for the left channel.
In Bridged monophonic operation of the amplifier, only
the lower (“Right”) input jack is used.
For bi-amplification: If you are using an electronic cross-
over to bi-amplify your loudspeakers, then the main output
cables from your preamplifier should go directly to the input
of your crossover unit. The “low” frequency output from the
crossover must then be connected to the inputs of one power
amplifier (such as this NAD unit), while the “high” frequency
output from the crossover is connected to the inputs of a
second power amplifier (another NAD amplifier like this one,
or to the power-amplifier section of your integrated amplifier
or stereo receiver).
2. SOFT CLIPPING
When an amplifier is overdriven beyond its specified
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 minimizes audible
distortion when the amplifier is overdriven. If your listening
involves moderate peak power levels, the Soft Clipping may
be left OFF. But we recommend that it be switched ON when
playing music at very high levels that might exceed the
amplifier’s power capacity.
3. SPEAKER IMPEDANCE
The impedance of a loudspeaker varies with frequency,
and in many loudspeakers the impedance is lowest at the
frequencies where the highest power demands occur in
music. In many “8Q” loudspeakers this minimum impedance
is from 4 to 6 ohms, and in “4Q” speakers the minimum is
typically 3 ohms. If you connect two sets of speakers to the
amplifier, their combined impedance is approximately half
the impedance of either.
For these reasons, all NAD amplifiers and receivers are
designed to produce maximum power output into imped-
ances of 2 to 6 ohms at the 4Q (NORMAL) setting of the
Impedance selector. If you are not sure of the true imped-
ance of your speakers, or if you are connecting two pairs of
speakers, leave the Impedance switch at 4Q (NORMAL).
If you are using a single pair of loudspeakers whose
true impedance is above 6 ohms at all frequencies, you can
optimise the amplifier for maximum power delivery at this
higher impedance by re-setting the switch to 8Q (HIGH).
To prevent accidental re-setting, the Impedance switch
is held by a slotted bracket which is fastened by a screw next
to the switch. Use a small screwdriver to loosen the bracket
screw, turning it about a haif-turn counter-clockwise, and
then slide the switch to the 8Q (HIGH) position. The bracket
will move with the switch. Tighten the screw to secure the
switch in its new position.
CAUTION: If the impedance switch is set to 8Q (HIGH)
with loudspeakers whose true impedance is lower than 6
ohms, or with two pairs of speakers connected in parallel,
the amplifier will tend to overheat and shut down when
operated at high output levels. The amplifier will resume
normal operation after it cools; but such abuse could also
The exclamation point within an equilateral triangle is intended
to alert the user of the presence of important operating and
maintenance (servicing) instructions in the literature
“accompanying the appliance.