NAD 2155 - Speakers B; Status Indicators; Speaker Selector

To facilitate this, the two conductors comprising the
speaker wire in each channel are different, either in the color
of the wire itself (copper vs. silver) or in the presence of a
small ridge or rib pattern on the insulation of one conductor.
Use this pattern to establish consistent wiring to both speak-
ers of a stereo pair. Thus if you connect the copper colored
wire (or ribbed insulation) to the red amplifier terminal in
the Left channel, do the same in the Right channel. At the
other end of the wire, if you connect the copper colored wire
(or the ribbed insulation) to the red or positive terminal
on the left-channel speaker, do the same at the right-
channel speaker.
8. SPEAKERS B
A second pair of loudspeakers may be connected
to the amplifier, using the “B” group of terminals, in the
same manner as the connections made to the
SPEAKERS A terminals.
If the second pair of speakers is located near the first
pair and will be played simultaneously, then they must be
correctly phased with respect to the first pair as well as with
each other. But if the second pair of speakers is located
away from the first pair (in another room, for example) or will
not be played at the same time as the first pair, then their
phasing need not match that of the first pair. Of course, as
with any stereo speakers, the second pair still must be in
phase with each other.
The SPEAKERS B terminals may also be used to
connect an adapter unit for electrostatic headphones. The
black “—” terminals in each channel share a common ground.
Another useful option for the SPEAKERS B terminals is
to connect a second pair of speakers wired for “ambience
recovery,” enhancing the apparent spaciousness of stereo
recordings. Locate a pair of small loudspeakers along the
side walls of the listening area, slightly behind the main
listening area and as far as possible to the left and right.
(Often it useful to aim such speakers upward or toward the
rear, so that their sound reflects randomly off the walls
before reaching you.) Connect a wire from the (L+) terminal
to the positive terminal of the left-rear speaker, and a second
wire from the (R+) terminal to the positive terminal of the
right-rear speaker. Make no connection to the (L—) and (R—-)
terminals on the amplifier; instead, connect a wire from the
negative terminal of the left-rear speaker to the negative
terminal of the right-rear speaker. Thus wired, these rear
speakers receive the left-minus-right “difference” portion
of the composite stereo signal.
FRONT PANEL CONTROLS
1. POWER
Depress this button to switch on the amplifier and any
other equipment plugged into the SWITCHED convenience
outlet on the rear panel. To switch the power off, depress the
button again and release it.
If you prefer, you may leave the POWER switch perma-
nently engaged and turn the power on and off via a switched
AC outlet in your preamplifier.
2. PHONES
Plug stereo headphones in here. The circuit will provide
proper drive signals for all conventional stereo headphones
regardless of their impedance, with just one exception:
electrostatic headphones usually are supplied with an
adapter unit which must be connected directly to the
speaker terminals on the rear panel.
Before plugging any headphones in, turn down ‘the
VOLUME control for safety. And when you are not listen-
ing to the headphones it is wise to unplug them from the
PHONES jack. Otherwise, when not wearing the phones you
might inadvertently turn up the volume to a high level and
feed dangerously strong signals to the headphones.
You may freely use headphone extension cables. If you
want to use a headphone Y-connecior to drive two headsets
simultaneously, they should be identical models. Connecting
together two headphones that differ widely in impedance
usually will produce a substantial loss of volume in the
headset having the higher impedance (or in both).
NOTE: The PHONES jack is intended for use only in the
normal stereo mode of the amplifier. In the “bridged” mono-
phonic mode the PHONES jack will receive only an out-of-
phase mono signal.
3. STATUS INDICATORS
These three lights provide information on the status of
the amplifier.
The red POWER indicator illuminates when the amplifier
is on.
The PROTECTION indicator illuminates when the output
transistors overheat as a result of prolonged operation at
excessively high continuous-output levels or into very low
impedances. If this occurs the sound will automatically be
silenced. Switch off the power; when the output stage cools
the protection relay will click off, and normal operation can
be resumed.
The SOFT CLIPPING indicator illuminates when the
Soft Clipping switch (on the rear panel) is engaged.
4. SPEAKER SELECTOR
When only button “A’ is engaged, sound is heard only
from the loudspeakers connected to the SPEAKERS A
terminals on the rear panel. When only button “B” is de-
pressed, the SPEAKERS A terminals are shut off and
sound is heard only from the loudspeakers connected to
the SPEAKERS B terminals.
If A and B are both pressed, the amplifier’s output power
is fed to both sets of speakers in parallel. If both A and B are
disengaged (with the buttons OUT), both sets of speakers
are silenced.
Thus if you have your main stereo speakers wired to the
“A’ terminals and a set of extension speakers wired to the
“B” terminals, you can choose to hear only the main speak-
ers (by pressing button A), only the extension speakers (by
disengaging button A and pressing button B), or you can
activate both by depressing both buttons.
The amplifier’s output signal is present at the PHONES
jack at all settings of these buttons. When using headphones
it normally is advisable to switch OFF the loudspeakers by
setting these buttons OUT. Then your VOLUME control may
freely be used to adjust the loudness level in the head-
phones with no fear of overdriving the speakers or disturbing
neighbors.
If you have connected an adapter unit for electrostatic
headphones to the SPEAKERS B terminals, you can use the
SPEAKERS switches to select your main stereo speakers
(A) or the headphones (B). 5
If you have connected speakers wired for “ambience
recovery” to the SPEAKERS B terminals, you can use the
SPEAKERS pushbuttons to listen to conventional stereo
(A only), to switch off the main speakers and listen only to
the stereo L-minus-R “difference” signal in the rear speakers
(B only), or to listen to spatially enhanced stereo (both A and
B depressed). You will find that the stereo difference signal is
usually lacking in bass. If the difference signal is very weak,
the recording lacks stereo separation.