| The Isolator from The Cartridge
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Breaking the Cartridge/Arm Feedback Chain
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August 2005 |
I
fell in love with The Cartridge Man (the nom
de audio of Leonard Gregory) MusicMaker III
phono cartridge immediately. It did its
eponymous job so adroitly and with such
soul-satisfying grace that I felt it almost
boorish to analytically break down its
performance into constituent parts. The parts
were so well integrated into a larger whole
that sound per se was irrelevant: it made more
sense to talk about violins, oboes, clarinets,
drums and guitars than to talk about high
frequencies, midrange or bass. The
MusicMaker’s coherence is as it should be:
truly great audio products grab you musically.
Sonics are a subsidiary matter, a means to an
end. If a component forces you to listen to
its sound it’s a pretty good indication that
something’s wrong.
The
MusicMaker III’s inherent musical quality was
obvious with all the tonearm and phono stage
combinations with which I partnered it in my
review, further adding to my high estimation.
Being free from high-strung compatibility
issues and other thoroughbred neuroses ensured
that most users would be guaranteed
experiencing its unparalleled musical
rightness. My esteem only continued to grow
after I completed my review (this was a
cartridge I had to own) and when nomination
time for our Most Wanted Components Awards for
2005 came, The MusicMaker III was the
instantaneous and obvious choice. The Music
Maker III is a great cartridge, a true
masterpiece.
The cartridge has a reputation for working
particularly well with the Hadcock 242 Uni-pivot
arm, which I did not have available for my
original review. No particular mystery here:
The Cartridge Man’s design input into the 242
tonearm range helped optimize the performance
of that arm with the MM III. Continued
development of the cartridge’s performance has
resulted in a new product from Mr. Gregory
called The Isolator that aims to solve a core
problem of LP playback.
We all know that the stylus’ movement in the
record groove does more than simply generate a
content-laden electrical signal in the phono
cartridge’s generator; it also pumps
non-musical mechanical energy into the
cartridge body and through it to the tonearm,
and thus to the top half of the record playing
system. This ‘upward’ component of unwanted
mechanical energy is mirrored by its
‘downward’ component: that which is generated
into the record itself and thus to the platter
and the rest of the turntable. The spurious
mechanical energy affects the arm by exciting
its resonance nodes and further complicates
extracting the wanted signal by dumping
vibrations back to the cartridge, stylus, and
record surface. To further muddy the waters,
the unwanted energy can then go back up into
the arm again and cycle the process. Feedback.
Since this stray energy is not related to
capturing the evanescently small musical
signal, its presence serves only as a
corruption and distortion.
The most often articulated model of the
phenomenon is the old Linn/Rega standby. Their
solution to the problem has been rigidity.
Firmly bolt the rigid cartridge (Rega even
produces a torque wrench to allow this to be
done optimally) to a very rigid tonearm with
very tightly-toleranced arm bearings, and the
mechanical energy generated by the tracing
stylus will pass through the cartridge, flow
up into the headshell, continue along the arm
to its bearings through which it will pass
(and magically disappear?) into the turntable
itself. Actually the Linn model held that the
vibrations generated into the system should be
allowed to freely float in a closed loop –
upward and downward components meeting so that
there is no relative displacement of the
stylus. As a model, the Linn/Rega is very
attractive, offering a seemingly common sense
understanding of the energy/resonance effect.
The problem with all models, however, is that
they aid understanding by simplifying the
phenomenon they attempt to elucidate.
Practically speaking, models are only useful
as working models; that is to say, designs
based on their principles have to work. The
excellent musical results attained by Linn and
Rega in LP playback are certainly impressive:
for decades now, if one wanted music from
one’s LP playback system, Linn and Rega were
the default companies to which to go.
The music-making success of Rega and Linn
products would seem to validate their working
model, though it is clear that some of the
assumptions that underlie it are leaps of
faith and achieving the model’s goals are more
difficult in reality than they appear in the
abstract. Although the concept of ‘draining’
energy away from the stylus/record interface
is psychologically attractive, it ignores the
fact that the energy flow is not a one-way
street and there is no guarantee that the
rigid solution will deal with all the
superfluous energy generated. It is just as
likely that some energy, being closer in
essence to water than to automobile traffic,
will flow back into the cartridge/stylus and
be re-radiated back into the tonearm in a kind
of feedback loop. The Isolator is designed to
break that unwanted energy loop by isolating
the cartridge from the headshell. Not only
will vibrations be kept from passing into the
tonearm, but those originating in the tonearm
itself will not pass into the cartridge, and
thus, into the stylus. Rather than relying on
the arm tube/bearing-drain principle, the
unwanted energy is dissipated into heat before
it even reaches the headshell. Another way to
skin the cat and a most clever, elegant and
successful way at that.
The Isolator is a small rectangular sandwich
(3/4 “ W x 1” D x 1/8”H) whose top and bottom
are two thin stainless steel plates.
Sandwiched between the plates is the exotic,
purposed-designed, and very expensive
isolating material. This material, technically
a closed cell, cross-linked ethylene copolymer
structure, is somewhat springy and can be
damaged from excessive compression. The
Isolator fits between the phono cartridge and
the headshell, serving as an acoustic filter
between the two. The cartridge side has a
re-usable, and easily broken, contact adhesive
on its stainless steel plate which bonds the
cartridge to The Isolator; two protruding
shafts slip into the cartridge’s mounting lugs
to center and orient the cartridge. These two
shafts do not have nuts; the cartridge is not
bolted to The Isolator. From the top of The
Isolator protrude two captive bolts that
attach to the headshell by two nuts. These
nuts are to be tightened just barely enough to
keep the cartridge and The Isolator from
shifting position. Those trained in the Linn/Rega
school of brute-force cartridge nut-tightening
(and destroying) need particularly to beware.
Over-tightening the nuts will destroy the
Isolator’s isolating material and will render
the device useless.
The Isolator can be used with all tonearms and
cartridges where headshell space allows
positioning The Isolator (3/4” W and 1” D),
and where the cartridge’s top mounting
platform is flat and large enough to allow the
adhesive to hold the cartridge securely. The
arm will also need to be able to compensate
for The Isolator’s additional 2.6 grams added
to the vertical tracking force, and will also
have to allow raising the arm height by 1/8”,
or 5.4 mm, to compensate for The Isolator’s
additional height when installed.
Since The Isolator was originally developed
with the MusicMaker III cartridge in the
Hadcock 242 tonearm in mind, I began my
auditions there. The 242 Series of Hadcock
arms are available with a variety of tonearm
wiring choices starting at $859 for the basic
Export model and topping out at $1629 for the
Super Silver. The 242 Cryo arm that I used
uses VdH copper wire that is cryonically
treated and retails for $1359. Hadcock arms
have, in the past, been a somewhat underground
phenomenon in the US, largely due to lack of
easy availability. Now distributed by
AudioFeil International, who also distribute
all The Cartridge Man’s products, the
English-made line of uni-pivot arms should
make some fine musical noise here: the
performance of the MusicMaker III with The
Isolator in the 242 Cryo arm sets a high
standard for classical music playback.
Spindly and skeletal in construction, the
Hadcock 242 arm breaks with some conventions
of unipivot arm design. Unlike the absolute
tip of the standard unipivot’s pointed
bearing, the end of the upward-pointing
bearing on the Hadcock is shaped like a cone.
The sides of this cone contact 4 miniature
(1mm) brass ball bearings within the bearing
cup of the arm tube. Using the simile of the
tightrope walker (to which the unipivot arm is
often compared) the walker is no longer up on
one tiptoe, but can use his feet to grip the
rope. The arm definitely wobbles less than the
common variety unipivot arm, easing the
fiddliness of operation, and banishing that
heart-stopping vision of the cartridge rocking
side-to-side when it first contacts the record
– a vision all too likely to raise concern
about the long-term effect on the stylus
cantilever and the record groove itself.
The Hadcock’s skeletal headshell, available
with both threaded and un-threaded screw
holes, is completely removable, and attaches
to the arm tube via a collar that slides along
the outside of the internally-damped stainless
steel arm tube. A set-screw fixes its
position, allowing both over-hang adjustment
and side-to-side rotation for azimuth
alignment. The arm tube itself can also be
rotated by loosening another set-screw on the
bearing cup. Together with the twin balancing
counterweights for adding tracking force, and
the outrigger rod extending from the bearing
cup that serves as the anchor for the thread
and bob-weight anti-skate control, there are a
wide variety of adjustments possible to make
sure the arm is balanced and perpendicular,
the bearing vertically aligned, and the
cartridge/stylus correctly aligned for
overhang and azimuth. There are also almost
infinite ways to screw this up and on a
unipivot design, this can lead to great
uncertainty as to accuracy of set up. Given
that a unipivot is inherently unstable once it
begins playing a record, making sure all the
balancing and alignment is correct is
absolutely crucial to maximize performance.
There is thus a high degree of fiddliness
involved to be sure, but the Hadcock is rather
straightforward to set-up and use, as long as
one is conscientious. The owner’s manual could
use a proofreader, though, as text content and
illustrations don’t completely match. The
entire arm wand assembly can be removed by
detaching the wiring connector on the arm
pillar, thus allowing easy cartridge swaps by
purchase of an additional arm wand.
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