SME engineers,
recognising the potential of the latest
complementary equipment, accepted the
challenge to design and build a pick-up arm
which unlike others in existence would make
no detectable sound contribution of its own.
The work took almost four years and the
measure of its success is the acceptance of
the Series V precision pick-up arm by
technical experts and users as one of the
world's truly great audio products.Series V
sound has an almost startling dynamic range
and neutrality enabling high levels to be
enjoyed. It escapes the 'LP' sound and
demonstrates that structural resonances in
pick-up arms are responsible for much that
makes vinyl records readily discernible from
master tapes.
The functioning of a pick-up arm appears
simple but is in fact very complex. All
cartridges employ relative motion between
armature and stator portions of a generating
system to produce the signal output.
Reproduction can only be true therefore when
all movement representing groove modulation
is made by the armature to which the stylus
cantilever is attached and none by the
stator represented by the cartridge body.
Unless the pick-up arm holds the latter
against even the minutest movement at audio
frequencies the signal will be modified in
some way. The result is a subtle loss of
clarity, dynamic range and transient attack
that can make the sound from even the best
system tiring to listen to.
The following notes will help a better
understanding of the problems and how they
were resolved in this radically new design.
In common with any mechanical device the
behaviour of a pick-up arm is governed by
three properties of matter that also define
the laws of motion. The first property is
mass which opposes any change in motion. The
effective mass of an arm and cartridge
resists motion least at low frequencies but
increasingly as frequency rises. It is this
resisting force which makes the operation of
a cartridge possible. At subsonic
frequencies the armature and stator move as
one allowing the slow movements needed to
negotiate the record surface without
generating a signal. At audio frequencies
however the increased resisting force causes
the armature to move relative to the stator
and a signal is produced. The transition
point between these two conditions is
important for a clean low frequency response
and is established by the compliance of the
cartridge and the total effective mass of
the arm and cartridge body.
The second property is stiffness which
resists bending or flexing. It is a
restoring force, proportional to position or
deflection.
The third property is damping or resistance
to motion. Here motion means velocity and
without it there is no damping. The total
equation of force acting on a pick-up arm is
therefore the sum of three parts:
acceleration acting on the mass, velocity
acting on the internal or applied damping,
and bending or deflection acting on the
stiffness.
Mass and stiffness determine how much a
pick-up arm will flex and vibrate and
damping determines how long it will vibrate.
Damping alone cannot prevent flexing or
vibration, it can only lessen its effect.
The stiffer the arm the less it will flex
and vibrate; the more massive the less it
will vibrate.
Very high tone arm mass would therefore be
ideal to control the cartridge had it not to
be strictly limited to preserve the required
relationship of compliance and mass already
referred to. Stiffness, the second part of
the equation of force, must therefore be
used also. Infinite stiffness would be ideal
but we have to be more realistic. In a beam
of given length stiffness is dependent on
the material used, its cross-sectional area
and in the case of a cylindrical beam
increases as the cube of its diameter.
Doubling the diameter will make it eight
times as stiff.
Although the proportions of the Series V
tone-arm reflect these facts, tests showed
that the required stiffness was still
unattainable using conventional fabricated
construction. A one-piece die-casting in
magnesium alloy was therefore adopted
comprising the shell, tube and balance
weight cantilever. 36% lighter but only 25%
less stiff than commonly used aluminium, a
magnesium arm of the same mass could be as
much as 25% stiffer. In addition die-casting
would allow the numerous changes of section
required to optimise effective mass and
control standing wave effects. Finally
magnesium's high self-damping factor was
augmented with an internal constrained layer
to damp the tubes’ high frequency resonance.
The Series V's excellent vibration analysis
results owe much to the high stiffness and
damping of its tone-arm, but stiffness to be
of value must refer to something rigid.
Tests disclosed the many points at which
rigidity could be lost so all other
principal parts were pressure die-cast
allowing each to be tailored precisely for
its purpose and utilising the high mass of
zinc-based alloy to damp out vibration.
Ultra-high quality 10mm and 17mm ABEC 7
radial shielded bearings were selected to
provide low friction vertical and lateral
movements, while holding the tone-arm
motionless against front/back and torsional
forces. The support afforded by these large,
wide contact angle bearings, excludes the
possibility of chatter and wear or damage in
normal use.
The horizontal axis bearings carry the
tone-arm in a substantial yoke also housing
a spring tracking force mechanism. The
bearing axis is at record mean level to
minimise warp-wow effect and the spring, a
possible source of coloration, is resonance
controlled.
The main pillar is 23mm diameter, machined
from steel, heat treated, ground and honed.
It houses the vertical shaft and bearings,
and carries the control bracket
incorporating the anti-skate mechanism,
lowering/raising control and motion damper.
The base is highly original. The pillar
moves vertically between two jaws and
horizontally between two slideways. Locking
is effected by transverse clamp bolts,
spring loaded to maintain settings when
released. The design ensures extremely
positive clamping maintaining the rigidity
of the assembly which is then secured to the
mounting surface of the deck with four
cap-head screws.
The weight housing is undersung to correct
its centre of gravity and provide a
vibrationally non-reflective termination of
the tone-arm. A damped two-point suspension
carries the tungsten-alloy balance weight .
Its unique shape enables it to be positioned
close to the fulcrum reducing inertia to
minimise the effects of record warp and
eccentricity.
Movement is made along
mitre-ways by rotating a thumb wheel and
leadscrew carried in twin ball races. Only
l9mm of travel is required to cover the
whole balance range and a lever effects
clamping in any position.
Electrical aspects received no less
attention. The internal wiring is of
specially developed silver litz, each
conductor having five insulated strands. The
damped output-socket swivels allowing it to
take up its own position for installation
and to minimise vibration transmission when
used on a sub-chassis. The high quality
linear crystal oxygen-free copper audio lead
selected for its electrical and mechanical
characteristics is terminated at one end
with SME right-angle 5-pole DIN contra-plug
and gold-plated phono plugs at the other.
The magnesium tone-arm is finished in satin
black enamel, other major parts in black
chrome with details in bright chrome and
polished stainless steel. Each unit is
complete with tools, accessories, and an
advanced drill jig/template and alignment
system simplifying mounting and exact
placing.
Structurally inert the Series V embodies
every worthwhile feature in a pick-up arm.
As part of a complete system working in
concert with a comparable turntable and
cartridge it will provide wide range
transparent reproduction of vinyl L.P's,
bringing the listener audibly closer to the
clarity and dynamics of the original
performance.
- Unique one-piece
pressure die-cast tone-arm utilising the
advantages of magnesium, replace
conventional fabricated construction.
- Internal
constrained layer damps minute residual
vibration leaving the tone-arm acoustically
inert.
- Fine machined
cartridge platform, enamel free to
avoid interface resonance.
- A Stainless steel
cross shaft, ground and thread ground.
Carried in massive yoke on 10mm ABEC 7 ball
races. Axis at record mean level to minimise
warp-wow.
- Dynamic balance
graduated vertical tracking force (VTF)
control applies 0-3g x 0.125g through
resonance controlled spring.
- Unique assembly
gives high rigidity and allows bearings to
be critically adjusted before tone-arm is
fitted.
- Stainless steel
vertical shaft, ground and thread ground,
with integral 16mm diameter flange to couple
shaft and yoke.
- 23mm diameter steel
pillar, heat treated, ground and honed,
carries two 17mm ABEC 7 ball races, widely
spaced to resist tilt.
- Anti-skate control
operates through tension spring and
filament. Dial corresponds with VTF and has
positive OFF position.
- Lowering/raising
control gives smooth positive action. Height
of lift can be adjusted.
- Subsonic lateral
mode fluid damper can be instantly adjusted
or cancelled.
- Dual-lock base
provides movement control with high
rigidity.
- Tungsten-alloy
balance weight carried on damped two-point
suspension. Extra-low inertia design assists
warp riding.
- Underslung weight
housing corrects centre of gravity and
provides non-reflective tone-arm
termination. Adjustment leadscrew journalled
in twin ball races with lever clamping.
- Swivelling damped
output socket minimises vibration
transmission in sub-chassis use.
- Fine adjustment of
arm height (VTA).
- Reference lines on
tone-arm facilitate VTA setting.
- Fine adjustment of
horizontal tracking angle (HTA).
- New design
alignment protractor sets HTA with greater
accuracy.
- Advanced
jig/template system guarantees correct
positioning.
