Nad 7155 Owners Manual

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STEREO RECEIVER

INSTRUCTIONS
FOR INSTALLATION
AND OPERATION

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REAR PANEL

1. AC Une Com. 9. Phone ham.
3. AC Convenience Outlets 10. Phone CapaciIance.
(N01 In European models) 11. CD/Aux Input.

3. Speakers A. 12. Tape! Rec/Play.

4. Speakers 5. 13. Tape 2 flee/Play.

5. Anlenna TermInaIs. 14. Preamp Om. Main In.

6. AM Rod Anlennn. 15. Son Clipping.

7. Phone GmundI 18. Speaker Impedance

5. MMIMO. 17. Bridging.

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FRONT PANEL
1. Pewm. 12. Low Level.
2. Phones. 13. Loudness Compenullon.
:1. Speaker Selectov. Ia. VolumeIBeIanoe.
4. Bass. 15. mning Display.
5. Tveble. 18. Stem: Indicalors.
e. Bess E0. 11. Pre-sms.
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10. Recording Input Salaam. 21. Search.
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local medium-wavelength AM radio stations. The rod is
mounted on a pivot. For best reception. swing it away Irom
the metal chassis of the receiver.

7. PHONO GROUND

If your turntable is equipped with a grounding wire
(usually a green wire laminating in a U-shaped spade lug).
connect it to this terminal. Turn the thumbvnut counter-
clockwise. place the spade lug under the nut, and tighten
the thumb-nut clockwise to secure the lug. It the grounding
wire has no spade lug. strip oil 1 cm of insulation to expose
the bare wire. twist the wire strands tightly together. insert
the wire though the small hole in the shalt of the Ground
terminal. and tighten the thumb-nut to lasten the wire
in place. ,

If you encounter a persistent low-level hum or buzz in
the sound. connect a wire from the Ground terminal to a this
earth-ground. Le. a copper-plated rod driven several feet into
the earth. A substitute electrical ground may also prove
effective: a cold water pipe. a steam radiator. or the third
hole of a modern electrical wall socket. In some cases
reversing the orientation at the AC power plug in the wall
socket may yield a reduction in hum level.

a. MMIMC

This switch sets the input sensitivity and gain oi the
phono preamplifier circuit. Set it according to the output level
of your phone cartridge. Set the switch at MM tor cartridges
oi the moving magnet. induced magnet. moving flux, and
moving iron (variable reluctance) types, and for high-output"
moving-coil pickups. i.e.. those with a rated output at 1.0 mV
or greater. It your cartridge is a Iowoutput moving-coil pickup

(with a rated output at less than 1.0 mV). set the switch at MC.

Here is another way to determine the preferred setting oi
the MM/MC switch. Begin by setting it to MM. After you have
completed the installation and wiring oi the system. play a
record. thh the front-panel LOW LEVEL button OUT you
should obtain a satislyingly loud volume level with a VOL-
UME control setting between 9 o'clock and 3 o'clock. It you
have to turn up the VOLUME control beyond 3 o'clock to get
adequately loud sound. turn the VOLUME back down and
reset the MM/MC switch to MC.

9. PHONO INPUT

Plug the signal cables from your lumtable into these
jacks. It the cables or plugs are color-coded. rater to your
tumtables instruction manual to team which cable or plug
is for the Left channel (upper lack) and which tor the Right
(lowerjack). Be careful to insert each plug fully into the
socket so that the plug's metal skirt fits tightly over the
exterior of the socket. It necessary. crimp the plug's metal
skirt slightly so as to obtain a tight lit with the socket.

to. PHONO CAPACITANCE

This switch selects the input capacitance at the phone
preampliller. It enables you to optimise the load capacitance
Ior those cartridges whose frequency response is attected by
this parameter.

It you are using a low-inductance pickup (such as a
Grado or Micro-Acoustics), or smearing-coil cartridge. than
the setting of the CAPACITANCE selector is unimportant. But
with many high-inductance magnetic pickups the capaci-
tance setting will audibly alter the sound oi the pickup.

in order to select the best value of preamp input capaci-
tance you must tirst determine the total capacitance recom-
mended for the cartridge. This usually will be included in the
maker's specifications. and it may also be mentioned in
magazine reviews oi the cartridge.

Next. subtract the capacitance oi your tumtable's tone-
arm wiring and signal cables. (Check the specifications

supplied with the tonearm. or write to the manulacturer oi the
tonearm, or as a last resort assume atypical value oi 150
pF.) Atter this subtraaion. what remains is the desired value
oi preamp input capacitance. Set the CAPACITANCE selec-
tor to the nearest value. It is not necessary to match the
computed value exactly; with most phono pickups a variation
01 50 pF one way or the other will produce only a very slight
change in frequency response.

Example: suppose you are using a Stanton 881$ pickup
cartridge in a Pioneer turntable. Stanton specifies a recom-
mended load capacitance of 275 pF for the cartridge. and
the Pioneer turntable has a cable capacitance of about 100
pF. Subtracting: 275 minus 100 equals 175 pF. so you should
set the CAPACITANCE selector to the nearest value, 200 pF.

It you prefer. you may simply set the CAPACITANCE
selector by ear while listening to recordings that are strong
in high-trequency overtones. Typically. when the capacitance
is too low the upper-midrange (the soprano voice range) will
be soltened and the response at the highest frequencies will
be peaky. leading to edgy violin tone and increased surface
noise. Too high a value at capacitance will bring the upper-
midrange forward while rolling oil the extreme highs.

11. CD/AUX lNPUT

Connect the audio signal cables lrom a digital Compact
Disc player to these jacks. The input signal will be led to the
Volume control belore reaching any active circuitry. so the
amplitier's circuits cannot be overloaded by high-level sig-
nals lrom the digital player.

It you don't have a CD player. any other line-level"
signal source may be connected here. such as a spare tape
deck, the audio line output lrom a videocassette or videodisc
player. or a television sound tuner.

On this product the upper jack in each pair is tor the Left
channel. and the lower jack is tor the Right channel.

12. TAPE 1 INPUT/OUTPUT

The tape connections may be used with recorders of
all types: cassette. micro-cassette. open-reel. digital, etc.
To make recordings, connect a stereo patch cord from the
amplifier's TAPE 1 output (REC) jacks to the recorder's LINE
IN jacks (not to its microphone inputs). To play back tapes.
connect a stereo patch cord from the recorder's LINE OUT
iacks to the amplifier's TAPE 1 input (PLAY) jacks.

13. TAPE 2 INPUT/OUTPUT

These iacks allow you to connect a second tape re-
corder of any type, and the ampliiier is wired to permit
copying tapes from one recorder to the other. Connect a
cable from the TAPE 2 output (REC) jacks to the recorder's
LINE IN tacks, and another cable from the recorder's LINE
OUT jacks to the TAPE 2 input (PLAY) jacks.

The TAPE 2 iacks may be used for a signal-
processing accessory instead of a second tape recorder.
Examples 01 such accessories include a dynamic range
processor, a dynamic noise filter. a DBX disc decoder, or any
other device whose operation depends on the setting at a
signal threshold. Connect a patch cord irorn the TAPE 2
output (REC) jacks to the processor's inputs, and another
patch cord irom processors outputs to the TAPE 2 input
(PLAY) jacks.

Other signal processing accessories. such as a graphic
equalizer or the special equalizer supplied with some loud-
speakers (e.g.. Bose. Electra-Wales. KLH) may be connected
either to the Tape jacks or at the PRE-OUT jacks. The choice
is a matter oi convenience.

14. PREAMP OUT, MAIN IN
Each channel of the amplifier includes two independent
sections or stages: the control preamplifier (including the

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phono preamp and most item-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 (alter first switching OFF
the POWER). you can connect various signal-processing
accessories in the path between preamp and power amp:
an equalizer, a time-delay ambiance reproducer. a stereo
image enhancer. an electronic crossover. etc. To use a signal
processor. connect a stereo patch cord lrom the FEE-OUT
jacks to the processor's line-level input lacks. and a second
patch cord Irom the processor's output lacks to the amplifi-
er's MAIN-IN jacks.

NOTE: any signal processor whose operation depends
on the setting ol a threshold. such as a dynamic noise filter.
should be connected to TAPE REC/PLAY jacks-where the
signals are unatlected by the amplilier's volume and tone
controls-rather than to the PHEOUT jacks.)

it 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. It 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 at an elaborate
audiophile sound system. The preamp output is capable at
driving several power ampfifiers simultaneously. or at 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).

15. SOFT CLIPPING

When an amplifier is overdriven beyond its specified
power output it normally produces "hard clipping" ot the
signal with harsh distortion and power-supply buzz as the
output transistors saturate. The NAD Solt Clipping circuit
gently limits the output wavelorm and minimizes audible
distortion when the amplifier is overdriven. II your listening
involves moderate peak power levels. the Solt Clipping may
be leIt OFF. But we recommend that it be switched ON when
playing music at very high levels that might exceed the
arnplifier's power capacity.

16. SPEAKER IMPEDANCE

The impedance oi a loudspeaker varies with lrequency.
and in many loudspeakers the impedance is lowest at the
trequencies where the highest power demands occur in
music. In many 80 loudspeakers this minimum impedance
is irom 4 to 6 ohms. and in 4n" speakers the minimum is
typically 3 ohms. It you connect two sets ol speakers to the
amplitter. their combined impedance is approximately hall
the impedance at 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 40 (NORMAL) setting at the
Impedance selector. It you are not sure at the true imped-
ance at your speakers. or it you are connecting two pairs 01
speakers. leave the Impedance switch at 40 (NORMAL).

It you are using a single pair oi loudspeakers whose
true impedance is above 6 ohms at all lrequencies. you can

optimise the amplifier tor maximum power delivery at this
higher impedance by re-setting the switch to 80 (HIGH).

To prevent accidental re-setting. the Impedance switch
is held by a slotted bracket which is tastened by a screw next
to the switch. Use a small screwdriver to loosen the bracket
screw. turning it about a hall-tum counterclockwise. and
then slide the switch to the en (HIGH) position. The bracket
will move with the switch. Tighten the screw to secure the
switch in its new position.

CAUTION: It the Impedance switch is set to 80 (HIGH)
with loudspeakers whose true impedance is lower than 6
ohms. or with two pairs ot 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 alter it cools; but such abuse could also
cause internal tuses to blow in order to protect the amplifier.
II this occurs. return the amplifier to your dealer tor service.

17. BRIDGING

This switch bridges" the two power amplifier channels
to term a monophonic amplifier with more than double the
output power. To convert to bridged operation. the lollowing
procedure should be Iollowed.

(1) Switch OFF the POWER.

(2) Be sure that the IMPEDANCE switch is set to 40
(NORMAL). II it is at 80 (HIGH). re-set it to 4D (NORMAL)
and secure the bracket to prevent the impedance switch
trom being moved accidentally.

NOTE: in the bridged mode the loudspeaker's imped~
anoe is ellect'rvely halved as seen" by the emplitier. An
B-ohm load looks like 4 ohms. a d-ohm load looks like 2
ohms. and pairs at 4-ohm speakers operated in parallel will
look like a t-ohm load. Driving paralleled low-impedance
speakers to high levels will cause the amplifier to overheat
and shut down. or may cause Internet Iuses to blow in order
to protect the amplifier. For best results the bridging rnode
should be used with a single bohm or a-ohm speaker in
each channel.

(3) Disconnect the metal jumper or signal cable lrom
the Lott-channel Main input to the power amplliier section at
the amplifier. Leave the Flight-channel jumper in place from
PRE-OUT to MAIN~IN. In the bridged mode the amplifier is
driven only through its Right-channel Main input. (For stereo.
the Lettchannel PFIE~OUT signal must be used to drive a
second. separate power amplifier.)

When two bridged amplifiers are used tor stereo, this
NAD amplifier drives the Flight" speaker. The other amp is
connected to the "Lell " speaker. II another NAD amplifier in
bridged mode is used tor the second stereophonic channel. it
too will be driven through its Right" Main input. even though
it is connected to the Lelt speaker.

(4) Disconnect any speaker wires from both the SPEAK-
ERS A and SPEAKERS 8 terminals. Separate the conduc-
tors in the cable lrom the speaker that is to be driven by this
bridged amplifier. Connect the "positiveoonductor to the
H + terminal and the negative" conductor to the t. + terminal
(La. to the two red terminals in the "A" group). DO NOT
connect any wires to the black terminals (R - and L - ).

It you want to drive two speakers in parallel. connect the
second speaker's leads to the red (PH and L+) terminals in

The lightning flash with arrowhead. within an equilateral
triangle. is Intended to alert the user ol the presence oi

sure; that may be at sullicient magnitude to constitute a
risk oi electric shock to persons.

uninsuleted dangerous voltage~ within the products endo-

lhe exclamation pornt within an equilateral trlangle is Intended
to alert the user at the preseme ol important operater and
maintenance (servicing) instructions in the literature
accompanying the appliance.

Page 9

Using a signal processor. If you have a signal pro-
cessor (such as an equalizer or a DBX unit) connected
to the TAPE 2 REC/PLAY jacks. you can use it to process
the playback signal from any program source by selling the
RECORD selector to the program source that you want to
hear. Then set the LISTEN selector to the same input to
hear the unprocessed signal. Or to TAPE 2 to hear the
processed signal.

For example. if you have a DBX decoder connected to
the TAPE 2 jacks. you can use it to decode DBX-encoded
records by setting the RECORD selector to PHONO. This
will teed the preamplified phono signal through the decoder
via the TAPE 2 REC/PLAY jacks. Than set the LISTEN
selector to TAPE 2 to hear the decodedsignal.

If you want to use, an equalizer. DBX encoder. or other
device to process a signal belcre recording it. you must
disconnect the tape recurder from the amplifier's REC/PLAY
jacks. Connect only the processor to the amplilier's REC/
PLAY jacks (either TAPE 1 or TAPE 2). and connect the tape
recorder to the processors own TAPE record/play jacks.

11. LISTEN

This rotary switch selects the signal that you will hear.

It you have a three«head tape recorder and wish to
monitor its playback output while a recording is being made.
use the RECORD selector to select the desired input signal
and feed it to the recorder. Then set the LISTEN selector to
TAPE 1 or TAPE 2 (as appropriate) to hear the monitor
output from the recorder.

Similarly. if you have a signal processor connected to
the TAPE 2 jacks and want to hear the processed signal. first
use the RECORD selector to choose the desired Input signal
and feed it to the processor. Then set the LISTEN selector to
TAPE 2 to hear the processed signal.

12. LOW LEVEL

This button reduces the volume oi the amplilied sound
by approximately 20 decibels. It has no effect on the signal
fed to the TAPE OUT (REC) jacks for taping or processing.
The LOW LEVEL switch has several practical uses:

. It extends the useful range of the Volume control. With
high-output signal sources. with efficient loudspeakers. or
with sensitive headphones. you may find that the sound is
too loud over most of the range of the Volume control. so that
you are restricted to using only settings near the lower end
of the control range. In this case. engaging the Low Level
switch to reduce the output level will allow you to use the full
range of the Volume control tor normal listening.

- It provides optimum signat-tonoise ratio lor low-level
listening in quiet environments. For example. if you are
listening to soft music late at night when the surroundings
are quiet, the Low Level switch minimizes the already-low
residual noise of the preamplifier and tone-control circuits.
ensuring noise-tree listening.

- It provides a convenient temporary out in volume. to be
used while answering the telephone for instance. When the
button is pressed again and released. it restores the volume
precisely to the preset level.

13. LOUDNESS COMPENSATION

This button engages a loudness compensation circuit
which. at low-tomedium settings of the Volume control.
boosts the bass response at the amplilier in order to com-
pensate for the human ears diminished sensitivity to low-
frequency sounds at low loudness levels. The circuit also
provides a slight treble boost to overcome the masking
of subtle high-frequency details by background noise.

Instead ol using this button. you may prefer to use the
tone controls and BASS E0 to obtain the tonal balance that
sounds most natural to you. at any volume level.

14. VOLUME/BALANCE

The knurled outer ring at this twosection knob is the
Volume control. which adjusts the overall loudness ol the
sound. The control is designed for accurate tracking of the
two channels. so that the stereo balance will not shift
noticeably as the Volume control setting is varied.

The center section of the dual knob is the Balance
control. which adjusts the relative levels of the left and right
channels. A datent at the 12 o'clock position marks the point
of equal balance. Rotation of the knob to the right (clock-
wise) decreases the Ievel of the left channel so that only the
right channel is heard. thus shitting the sonic image to the
right. Rotation of the knob to the left shifts the sonic image
toward the left speaker.

Adjust the Balance control to produce a natural spread
of sound across the space between the speakers. with any
monophonic sound (such as a radio announcar's voice)
appearing as a phantom image centered midway between
the speakers.

Ideally the detented center position ol the Balance
control would be its normal setting. But several common
circumstances may cause an unequal balance between the
channels. requiring a compensatory oll-canter setting at the
Balance mntrol to restore the most uniform spread at stereo
sound between the speakers. Examples include unequal
output from the two channels of the phono cartridge. dilfer-
ent acoustical environments around the two loudspeakers.
or simply a listening position that is closer to one speaker
than to the other.

These controls do not alfect the signals fed to the TAPE
RECording jacks.

15. TUNING DISPLAY
This display is in three parts: frequency. signal strength.
and tuning.

Frequency. The display shows the tuning band and the
lrequency to which the tuner is set. for example "FM 103.70
MHz or "AM 1290 kHz." The fifth digit of the FM frequency
display is reduced in size and brightness. In Europe and
elsewhere the Iiith digit will be either 0 or 5 since the tuning
increment is 0.05 MHz.

Signal Strength. The signal strength meter is a series of
five bars. The number of illuminated bars increases with the
strength of the received signal. It only one or two bars
illuminate, the signal is too weak for noisa~frae reception in
stereo. but reception may be satisfactory in mono. Strong
signals are indicated by four or live illuminated bars. If fewer
than four bars are illuminated when you are correctly tuned
to a station. then you are not getting all of the noisequieting
in stereo that the tuner is capable of. and a better antenna
(or a re~aiming of your present antenna) is needed in order
to pull in a stronger signal.

Timing. The center-tuning indicator (FM only) consists of
an illuminated rectangular bar (like those in the signal
strength meter) flanked on either side by a triangular pointer.
The triangular pointers illuminate to indicate that the tuning is
within an FM stations channel but not at the center of that
channel. The pointer shows the direction that the tuning must
be shilted in order to tune the station correctly When you are
accurately center-tuned the triangular pointer fades out and
only the middle bar is illuminated.

On the AM band. tune for maximum signal strength.

15. STATUS INDICATORS

The PM STEREO indicator illuminates when a stereo
FM broadcast is received and decoded. Note that if the
MONO button is engaged, all broadcasts will be received
in mono.