Free Audio Service Manuals - Free download Nad 5120 Owners Manual

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but virtually permanent spectrum of structural vibrations
caused by motors, furnace blowers, the compressors of
refrigerators and air conditioners, etc. When these vibra-
tions reach the phono stylus they tend to colour the sound,
especially if they are further amplified by the resonance of
the arm/cartridge system. (This resonance, due to the effec-
tive mass of the tonearm interacting with the compliance of
the stylus assembly, is usually found between 7 and 12 Hz
with modern high-compliance pickup cartridges.)

The suspension frequency of the NAD 5120 is much
lower: less than 4 Hz. Since the suspension ﬁlters out
vibrations above its resonance, this design provides the
most effective isolation of the record and stylus from the
commonest kinds of environmental vibration, and therefore
it offers the purest sound quality. The low suspension
frequency has a disadvantage, however. if large-amplitude
low-frequency vibrations reach the turntable they are more
likely to cause obvious and perhaps annoying misbehavior,
such as wow" (wobbly pitch) or even skipping of the stylus
between grooves. (Of course, unlike persistent cclcuration
of the sound, this obvious misbehavior is relatively easy to
identify and correct.)

If your listening room has a concrete floor, or if the
turntable is on a shelf that is fastened to a wall, such
vibration is unlikely to be a problem. But wooden floors often
have a springy low-frequency resonance of their own; danc-
ing or even walking on such a floor may produce large-am-
plitude vibrations that coincide with the turntables suspen-
sion resonance. If this occurs, the best solution is to place
the turntable on a massive object (such as a polished stone
slab or a cabinet filled with records), or to isolate the
turntable from the floor by placing it on a shelf that is
fastened to the wall.

APPENDIX B: TUNING
THE DYNAMIC VIBRATION ABSORBER

Recommended settings for the DVA frequency and
damping are listed in the enclosed leaflet for many popular
pickup cartridges. if no recommendation is available for
your phono cartridge, excellent results will usually be ob-
tained by setting the DVA frequency screw [25} to 10 Hz and
the DVA damping rod [18] to an intermediate value (Q =1 or
2). Precise settings of the DVA adjustments are not neces-
sary in order to obtain the benefits of the Dynamic Vibration
Absorber

However, if you want to conduct your own experiments
to determine the optimum DVA settings for your particular
cartridge, you will need a test record that has a frequency
sweep or a series of test tones recorded at a high level of
vertical modulation, spanning the range from about 15 Hz
down to about 5 Hz. A special NAD test record has been
created for this purpose, and it includes detailed instructions
for tuning and damping the DVA with any pickup cartridge.
The record contains a series of high-level "warble" tones
ranging in frequency from 5 Hz to 15 Hz. (Each warble tone
varies rapidly up and down in frequency over a1 Hz range
centered at the nominal frequency, in order to be certain of
picking up any very narrow resonances in the playback
system. E.g. the 5 Hz tone varies between 4.5 and 5.5 Hz.)

Superimposed on each infrasonic warble tone is a
steady 440 Hz tone recorded at a relatively low level. When
you play the record, ideally you should hear only a steady
440 Hz tone since the infrasonic warble tones are below the

normal low-frequency limit of human hearing. But when the
infrasonic tone excites the arm/cartridge resonance, the
stylus (and, to some extent, the cartridge body and tonearm
as well) will shake. This vibration may be large enough to be
visible to the unaided eye, it you look closely. In any case
the vibration of the stylus in the groove will produce an
audible warbling or flutter" of the 440 Hz tone, due to
frequency intermodulation distortion (F.l.M.).

The first step in DVA tuning is to measure the natural
frequency of the arm/cartridge resonance, which requires
that the countenNeight be immobilized. This can be done by
wedging some cardboard or styrofoam into the space above
and below the counterweight, so that the counterweight is
no longer free to vibrate on its spring. Another approach is
to screw the damping rod [18] down into the fluid to obtain
maximum damping (Q greater than 3); while this does not
completely immobilize the ccuntenrveight, it provides a suffi-
ciently stiff mechanical coupling between the arm and the
counterweight to allow an accurate measurement of reso-
nance frequency.

Then play the test record, listening for the flutter,"
pitch wobble, or warbling quality of the 440 Hz tone that is
caused by the arm/cartridge resonance. Play each band of
the record, and identify the band in which the worst flutter
occurs; or watch the cartridge closelyand note which band
causes the greatest visible vibration of the stylus assembly
and cartridge body. Use the voice announcement on each
band of the record to identify the frequency at which the
peak resonance occurs. (With some phono cartridges, the
440 Hz tone will be quite steady on some bands, in obvious
contrast to the pronounced flutter that is heard on the bands
where the peak resonance occurs. With other cartridges,
flutter will be heard over the entire 5 Hz to 15 Hz range
of the test record, and your task is to identify the band
or bands on which the greatest amount of audible
flutter occurs.)

Unscrew the damping rod [18]. or remove the shims
that you installed to immobilize the countenrveight, and
check to see that the counterweight is free to vibrate on its
spring. Turn the DVA frequency screw [25] until the lower tip
of the screw is aligned with the resonance frequency that
you have just determined from the test record.

Depending on the amount of internal stylus damping
in the cartridge. the resonance peak is likely to span a range
of frequencies rather than being sharply tuned to one
frequency. When in doubt, set the DVA frequency slightly
lower than the median resonance frequency. (For example,
if the peak resonance appeared to span the range from 8 to
12 Hz, set the DVA to 9 Hz.) This is for two reasons. (1) if
the arm/cartridge resonance is not completely cancelled by
the DVA, it is better to cancel the lower-frequency portion
of the resonance. leaving the relatively innocuous higher-
frequency portion of the resonance uncompensated.
(2) As damping is added, the added stiffness will tend to
raise the DVA frequency slightly above its nominal value.

The final step is to set the DVA damping rod [18]. With
most pickup cartridges the damping is uncritical, and the rod
should be set for a moderate amount of damping (0 =1 or
2). If you are using a cartridge that has an unusually small
amount of internal stylus damping (e.g. a Grado), you may
determine the optimum damping by trial and error: play the
test record several times, using different damping values.
to find the setting that yields the least audible flutter of the
440 Hz tone.

Nad 5120 Owners Manual

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