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Many thanks to Jean Nantais for this amazing contribution to the
website!
The #1 aim in getting
the most out of your Lenco is to bolt it securely and directly
to a big, heavy, non-resonant weight, in order to squeeze the
most performance out of the motor/platter/idler-wheel system.
You don’t want to use gaskets between the Lenco top-plate and
the plinth; what you want to do is to contruct an inert mass,
and make this mass One with the Lenco, in effect creating a
Super Lenco. The inert mass is achieved by using the principles
of “constrained layer damping”, intelligent choice of materials,
and the actual bonding agents used in the construction.
Problems with the Lenco
were due to the resonant boxes it was mounted in as well as
improper set-up. If you trolled through various websites you
will have noted that the Lenco is said by many to be very quiet,
while others claim it is noisy: the noise is due to improper
set-up, as I know from experience these are very quiet, and very
noisy without proper set-up. The issue is the motor: it must not
contact anything (including the plinth so this must be measured
and cut very carefully), the wheel must not contact anything but
the motor and platter, the motor must be swinging freely from
the springs. This said, the motor is very powerful, and the best
way to sink the vibrations is mass. Remember, as quiet as the
Lenco is, it has an extremely powerful motor, and this energy
still has to be dealt with to extract the most from whatever
tonearm/cartridge you end up choosing.
We now know that
resonant boxes are a big no-no in record-player design of any
sort, and this goes ten-fold for idler-wheels with massive
powerful motors and hollow metal top-plates. Most amateurs
cannot build attractive boxes and anyway this is a bad idea.
Simply cutting out slabs of lumber (or other materials) and
gluing them together is much easier to do (the slabs being cut
fairly accurately at Home Depot) AND is a better platform. In
avoiding resonant cavities, each successive slab will have less
cut out from it, which will result in higher overal mass, which
is a good thing. Since the dimensions of the beast means at
least 3" thickness, and at a minimum roughly 17" x 14", the
total resulting mass becomes necessarily very heavy and inert,
which is the central issue in rebuilding the Lenco and
extracting the maximum performance from it.
High mass is a Good Idea for all unsuspended decks, not just
idler wheels. Part of the secret of the Walker Proscenium is
it's extremely high mass. The Clearaudio 'tables become the more
expensive the greater the mass involved, and the performance
consequently goes up. Apply these principles to the Lenco, which
actually needs the high mass more than all these belt-drive
'tables, which can be done cheaply at Home Depot. It is also a
case of "Form follows Function": as the dimensions are intended
to shroud the internal parts for attractiveness, and this gives
a thickness of the plinth of at least 3 inches. The plinth also
should be both wider and deeper than the metal top-plate, again
for architectural attractiveness, but also to provide the room
for the tonearm board, whatever cover you find, and to show off
the final finish.
For "proprietary damping
material" there's carpenter's glue and contact cement, with the
judicious application of various damping materials such as
Dynamat for the Lenco's metal plinth, damping sheets available
at car parts stores.
For "constrained layer
damping", which is essentially mixing your materials so there
isn't a single resonant point (hoping for the best), consider a
mix such as MDF glued to a sheet of birch-ply, or chipboard
glued to a sheet of plasterboard for anti-resonance
characteristics (this requires a box, however, as the plaster is
naked), or a mixture of chipboard, MDF and Birch-ply and so on.
Be inventive, follow your theories! Remember, chipboard (really
cheap) is porous, so you will have to fill in the edge with
plaster or plastic wood before starting to paint. I don't think
solid MDF, which is easily cut and machined, is a good idea, as
it has an unattractive sonic signature (lumpy and uneven bass,
bright upper midrange). However, when sandwiched between other
materials, it works well, is cheap, and very, very heavy, adding
mass and being easily machined (wear a mask however when working
with it).
The bonding issue is a
complex one. While it is true that epoxy spreads more evenly, it
hardens to a glass-like consistency, and so adding potential
resonances (or perhaps beneficial stiffness), while contact
cement is itself a vibration-deadening agent (that "proprietary
damping material” manufacturers go on about). While the contact
cement will leave some tiny spaces, it takes care of more
problems than it creates, as the resulting mass is very dead and
very strong regardless. This is what you’ll need for gluing
slick plastic materials like Corian. After joining, move the
clamps around to clamp down all points of the two
contact-cemented surfaces, to make sure the bond is total. Of
course, if the whole thing is made of wood, then it isn't an
issue, just use wood glue. But be careful, as fast-drying wood
glue will ruin your plinth by setting before you have aligned
your pieces. Glue two slabs at a time, therefore, letting them
sit, clamped, and then glue another layer to the two glued
slabs, and so on until you’re finished.
The plinth's purpose is
to be totally passive, to, by the sole means of mass, halt the
attempts by various energies (the Mighty Lenco Motor, the
cartridge's attempts to move the tonearm at the base and thus
the whole turntable, etc.) to move the base on which the tonearm/cartridge
sits, so the cartridge's entire energies, created by following
the grooves in the vinyl, end up at the magnets or the coils
intact, and on to the phono stage and on. Imagine focussing ALL
the cartridge's energies like a laser beam at the phono stage.
So remember, you want a passive plinth, inert and immovable, not
an active comb filter, or a sponge at all frequencies which will
rob the music of its potential energies. In choosing your
materials, you want an end result which is "passive" and not
"active", meaning that though you don't want it to resonate
actively at any frequency (and constrained-layer-damping is the
way to achieve this as it prevents the natural resonant
frequency of any given material to express itself and be heard),
nor do you want it to absorb energies at any given frequency, or
across the frequency spectrum so that it actively damps the
cartridge's/music's natural energy. Given the preponderance of
space-age materials in modern turntable design, many high-end
'tables today are guilty of acting as "comb-filters", meaning
they damp/absorb energy at certain frequencies. For instance,
today acrylic is top of the pops in record-player design. If you
pay attention to the reviews, you will note that almost all
acrylic turntables have a characteristic clear sound, but seem
lacking in warmth. This is because acrylic damps energies in the
mid-bass, thus creating the illusion of greater clarity. This
robs the music of much of its presence, and messes with the
total recovery of the original performance. You don't want a
comb-filter. When choosing materials, ask, is it active and so
filtering out some energy? Hold the material up to your ear and
ping it with your finger. In the absence of scientific
instruments, a "feel" for the material is the only recourse. So
do your best to choose materials you trust to be neutral and
passive, and to avoid materials which sound like they might be
active. Not 100% accurate, as you must rely to a certain extent
on your instincts. A material which rings, like, say, marble, is
better than a material which absorbs and transforms vibration
into heat, as the ringing material can be damped by
constrained-layer damping. A material which actively subtracts,
however, will always be actively subtracting, no matter what you
do. So hold it up to your ear, try to judge if it is too active,
and go with your instincts. You can get the idea by doing this
with Sorbothane vs rubber, for instance. The rubber, while a
similar material in some ways, will still give a satisfying
"thud", and so is not too active. Sorbothane, on the other hand,
definitely is too active, and will actually absorb the energy so
that there is no thud of any kind. Some materials, as well, seem
hard, but like certain carbon-fibre formulations, actually
transform vibration into heat. So no carbon-fibre formulations
for a record-player, which however works great under amplifiers.
When in doubt, do some research and find out if the material is
used in any applications to transform vibration into heat.
Constrained-layer-damping definitely works to diminish the
contribution of any one material, so long as you don't go for
active vibration-killers like Sorbothane and certain carbon-fibre
formulations. Acrylic is not too active so long as it is layered
with other materials.
The massive, immovable
plinth (you don't need tons here, however, as powerful as the
motor and cartridge energies are, they have their limits) allows
the motor's energies to be directed solely towards spinning the
platter at perfect speed, which given the platter's flywheel
design the Mighty Lenco Motor (4-pole, cogless, dynamically
balanced, 1800 RPM, silent beauty!) can do. A truly passive
immovable plinth allows the great musical energies (like Star
Wars weaponry, focused and powerful) which results from perfect
speed to reach your phono stages intact. Result? What you've all
heard, musical reproduction which makes your collective jaws hit
the floor! Happy designing! |
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