|Lenco Plinth Building |
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!
Direct Coupling, which is building your plinth so the bottom of the top-plate under the platter rests on a layer, either directly or via a neoprene rubber gasket, is mandatory!!!. In this way the large non-resonant mass is maximized for effectiveness, acting as a true sink for vibration and noise, and seems magically to even draw away surface noise, so you’re your records also become much quieter. This shows the large non-resonant plinth REALLY works. The detail is more apparent, the surface noise diminished.
The reason I build such a large space around the motors is not only to avoid heat build-up, but to avoid the transmission/reflection of energies into the plinth. I have explained this at various times in the course of the thread, but here we go again: I had a Maplenoll Athena turntable (before the Ariadne version) which had a fluid-damping trough. When I put it on expecting a great improvement, what I got rather than better control and noise suppression of my cantankerous Decca cartridge, was a doubling of the noise. I couldn't understand it at the time, and I tried various grades of fluid in an effort to make it work. Then we went to a larger trough: problem solved. The walls of the original trough were too close to the paddle, and so reflected the already-existent noise back into the paddle, effectively doubling it. This is the principle as well of such open architecture 'tables as the Oracle: rather than enclose the workings in a resonant box, leave them exposed to the air where the resonances simply disappear into the air, reflecting off nothing. This is the principle as well I applied to the Prototype Lenco under my "system".
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