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patch cord from the processor's outputs to the TAPE
IN
(PLAY) jacks.
Other signal processing accessories, such as a
graphic equalizer or the special equalizer supplied with
some loudspeakers, may be connected either to the
TAPE
jacks or at the Preamp Out jacks. The choice
is
a matter of convenience.
13.
PREAMP
OUT,
MAIN
IN
Each channel of the amplifier includes two independent
sections or stages: the control preamplifier (including the
phono preamp and most front-panel controls), and the power
amplifier (which provides the power to drive loudspeakers).
In
normal operation the preamp and power amp are con-
nected together via factory-installed U-shaped metal jumpers
that bridge the PRE-OUT and
MAIN-
IN
jacks. Check to be
sure that they are fully inserted into the jacks and that
nothing
is
touching them.
By removing the metal jumpers (after first switchi
ng
OFF
the POWER), you can connect various signal-processing
accessories
in
the path between preamp and power amp:
an
equalizer, a time-delay ambience reproducer, a stereo
image enhancer, an electronic crossover, etc.
To
use a signal
processor, connect a stereo patch cord from the PRE-OUT
jacks to the processor's line-level input jacks, and a second
patch cord from the processor's output jacks to the amplifi-
er's
MAIN-IN
jacks.
NOTE:
any signal processor whose operation depends
on the setting of a threshold, such as a dynamic noise filter,
should be connected to TAPE REC/PLAY
jacks-where
the
signals are unaffected by the amplifier's volume and tone
controls-rather
than to the PRE-OUT jacks.
If you remove the metal jumpers, save them
in
case you
may want to disconnect the signal processor and return to
normal operation at a later time. If the jumpers should be
lost, a conventional stereo patch cord can be used to
connect PRE-OUT to
MAIN-IN
in
each channel.
This receiver can be used as the heart of
an
elaborate
audiophile sound system. The preamp output
is
capable of
driving several power amplifiers simultaneously, or of driving
the long signal cables required to connect to power amps
which are located near the speakers (or to "powered" active
loudspeakers with built-
in
power amplifiers).
14.
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 NAO 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.
15.SPEAKERIMPEDANCE
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 "8V" loudspeakers this minimum impedance
is
from 4 to 6 ohms, and
in
"4V" 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 NAO amplifiers and receivers are
designed to produce maximum power output into imped-
ances of 2 to 6 ohms at the 4V (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 4V (NORMAL).
6
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 8V (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 half-turn counter-clockwise, and
then slide the switch to the 8V (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 8V (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
cause internal fuses to blow
in
order to protect the amplifier.
If this occurs, return the amplifier to your dealer for service.
FRONT PANEL CONTROLS
1.
POWER
Depress this button to switch on the receiver and any
other equipment plugged into the SWITCHED convenience
outlet on the rear panel. The frequency display will illuminate
when the power
is
on.
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 use an external switch (such as a clock
timer) to turn the power on and off.
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-connector 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).
3.SPEAKERS
When this switch is set to
"
Pt
,
sound
is
heard only
from the loudspeakers connected to the SPEAKERS A ter-
minals on the rear panel. When the switch
is
set to "
B,
" the
SPEAKERS A terminals are shut off and sound
is
heard
only from the loudspeakers connected to the SPEAKERS B
terminals. At the "A+ B" setting the amplifier's output power
is
fed to both sets of speakers
in
parallel. At the "OFF"
setting both sets of speakers are silenced.
Thus if you have your main stereo speakers wired to the
"
/\
' terminals and a set of extension speakers wired to the
"B" terminals, you can choose to hear only the main speak-
ers (A), only the extension speakers
(B)
, or both (A+
B)
.
The amplifier's output signal
is
present at the PHONES
jack at all settings of the SPEAKERS selector switch. When
using headphones it normally
is
advisable to switch OFF the
loudspeakers. Then the VOLUME control may freely be used
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