AN OBJECT OF ART

According to various reviews at the time when the SP10 mkii was launched, many stated that the problem with the SL1000 (SP10 in the obsidian base plus feet) is that they measured some mechanical feedback when playing music relatively loud.

Hi-Fi Choice from Great Britain reported that the bass was somewhat slender and there was some shallowness in the mid and upper mid frequency region. This is certainly caused by the amorphous "structure" of volcanic glass (and any other glass often used for platters).

This criticism does not make the complete SL-1000, as the Technics engineers designed it as an entity, less desirable, less unique. In this way it can be considered as an example of industrial design as it was achieved in the nineteen seventies of the last century. Thus seen it is an object of art. But for sound reasons...

OBSIDIAN BASE FOR MK3

The Technics SP-10Mk3 is a completely different turntable. The opening for the motor in the obsidian base for the Mk3 is a round hole and it can not accomodate Mk2.

KANETA BASE FOR SP-10 MK3

It seems that the motor unit alone, which is the SP-10 Mk2, was sold in higher quantities. No wonder many audiophiles and designers construct plinths from wood which makes a sonic difference if wood is chosen with specific sound porperties: propagation and speed of sound, density of the material, and stiffness. That is why Akito Kaneta chose layers of a specific wood for his base of the Technics SP-10Mk3. In the picture at left (courtesy Richard Huxley from France), the Kaneta philosophy was applied, although in the original Kaneta version the SP-10 is stripped and just the motor unit with platter is mounted on the layered wooden plinth. Also the power supply was altered.

MANY ROADS LEAD TO ROME

In case you come accross an SP-10 Mk2 or Mk3 without the SH-10B3, there are several options to construct a base/plinth. You either can go the Cotter way and make the suspended type, or construct a solid plinth of several layers of wood, or even add thin layers of aluminum or sheets of steel in between the wooden pannels, and then place this plinth on rubber feet. Such a base or a similar construction can give a harmonious sound and better dynamics in the lower register and a firmer mid band. You know that if the bass is not firm, full and controlled, the rest of the spectrum suffers.

If you do not own the obsidian base you will have to construct a solid and relatively heavy base and de-couple it from its environment by means of insulating rubber feet. Various materials can be used for the base:

• multiple layers of particle board (chip board)
• plywood covered or combined with a thin sheet of aluminum (1 mm)
• layers of thin wood glued together
• serpentino (thin plate of stone, about 10 mm, with a sort of grainy and not too dense structure), andmbine it with a wooden panel, and there is - as some people suggest -
• corian.

Better not use corian as it has a frequency curve with emphasis on high frequencies, depending on the thickness. I have tried it for arm base and for a 5 mm thick turntable mat shaped according to the drawing on my page about . The properties of corian are not always as desired because the percentages of aluminum varies (large or small flakes, more or less flakes).

And better not use MDF, or sparingly because of its odd frequency characteristic which shows uneven sonic qualities with emphasis in the lower mid area. This anomaly may disappear when you use many layers and construct a very heavy base. But then the fact remains that it is in fact "dust", the dust particals pressed and bonded.

I myself am not an advocate of too heavy plinths made of materials with a high density. Better choose the material and the volume in accordance with speed of sound and an even frequency characteristic without abrupt filtering of the signal. In that case the sound dissipates gradually.

The data for stiffness, density and soundpropagation are important in order to get an idea of what the best combination of materials is. Look for the data of sound propagation in materials. A few data in the table at left are taken from The Practising Scientist's Handbook, written and compiled by Alfred J. Moses (Van Nostrand Reinhold Company, New York, 1978).

It is obvious that carbon has almost 3 times the speed of aluminum. Hence it is preferred by cartridge builders for the material of the cantilever. See also the difference between aluminum and acrylic. These materials have a significant effect on the measure of tangibility of the sound.

If certain materials are used in alternate layers, they team up very well for arm boards and chassis, whereas acrylic alone gives less definition and detail.

A wooden plinth coated with a thick, shiny layer of lacquer may influence the frequency characteristic in a negative way.

The frequency of the isolating rubber feet or springs supporting the base plate (the SP10mk2 unit included) should preferably be in the region of 2 to 4 Hz.

VARIATIONS

The choice of materials, the amounts used, and the position in the total concept determine the quality of a turntable, loudspeaker, amplifier, cd-player, cable, etc. In short: choice, amounts and topology can make or break the quality of the reproduction, deteriorate or improve the sound.
Most high-end components have been designed accordingly on the basis of a quasi unlimited budget. While in cheap, mass marketed audio systems the budget is the restrictive factor, the best solutions for the dollar have been sought by the engineers.
This adage naturally applies to the Technics SL-1000 Mk2 (SP-10Mk2 on plinth with cover) and though considered high end, it was produced in relative large quantities. Some reservations exist concerning the use of volcanic glass (obsidian) for the plinth and maybe the EPA 100 tonearm, but at the same time the system was optimized in other details, for example the addition of plywood to the small arm board which would have a somewhat counteracting, positive effect.

Shape and damping of the suspension in a light floating chassis turntable are extremely important. They are as important as size, contact area, and design (shape) of the feet for a turntable system mounted on a heavy plinth - be it of slate, volcanic glass or massive wood.
Diminishing mechanical feed back coming from external sources may seem the main objective, but springs and feet do play a role in damping vibrations in the chassis or plinth itself, as I found out.

Some time ago I obtained a second and perfectly working SP-10 Mk2 unit with the high quality EPA-A501 tonearm with exchangeable arm tubes (wands). The unit had previously been in use in a studio. It is mounted on a stone plinth made of slate measuring 550 x 440 x 28 mm. When installing the table it soon became clear that the top area of the rubber isolating feet influences the frequency characteristic significantly. The smaller the contact area of the top of the feet touching the underside of this slate plinth, the better the sound reproduction is (B).
But that is because this slate plinth of 2.8 cm thick can pick up vibrations. Therefor it is necessary to have a heavier plinth that will be inert to externl influences.

No matter how well the turntable system works, it will always be the result of a compromise. The lesser the compromise the better the sound.

At left a list of choices which will have a greater or lesser effect when designing a complete turntable system or when building just a plinth for an existing motor. Just for you to contemplate and decide what the plinth you want to construct should be like. Going heavy is a less complicated way if compared to designing/composing a plinth by using various materials which have their effect on increasing the harmonics and the transient.

ALBERT PORTER'S MK-2 BASE

The following pictures were send to me by professional photographer Albert Porter. They show the solid base he constructed for his SP-10 mkII with SME SME 312S (Magnesium), and Air Tight PC1 Moving Coil cartridge.
He made the plinth thicker and heavier than 30 mm to 35 mm (1-11/64 inch to 1-3/8 inch) which is the minimum, indicated on the original Technics mounting template of which he bought a real size copy from me.
He used multiple layers of Baltic Birch plywood, an aluminum sheet and Bass wood.

The massiveness of the plinth can be seen in the opening of the arm board and the room the tonearm base needs. The arm board has about the same thicknes as the top panel of plywood. The arm board is attached to two rectangular strips of thick brass. There are three threaded holes in each strip for mounting the arm board. This solution is very practical. It not only provides a secure and firm connection of arm base and platter (no bending mode), in this way various arms can easily be mounted.

This is the unfinished base with the SP-10 Mk2 mounted on it. It shows that the height of the base is substantial.

The plinth Albert Potter constructed does not rest on feet, spikes, rubber dampers, cones, or whatever is generally used for coupling such an important component to the environment. Albert states: "There is no need for suspension with this Technics as there is no feedback problem. The plinth as shown weighs 85 pounds (38 kg., Ed.) and sits in my equipment and software bookcase on a 2.5" (6,35 cm., Ed.) Maple butcher block shelf, approximately 20 feet (6 m., Ed.) from the speakers."

Well, how does it sound?
Albert writes: "My other turntable is a Walker Proscenium, which is one of the best turntables in the world. The Walker is fitted with the Koetsu Jade Platinum Signature. I would classify the two tables as somewhat equal and at the same time, different. The Technics seems to be as quiet and speed accurate as possible, but it is much more dynamic than the more expensive table. I am almost 100% sure that's due to the cartridge difference but plan on doing testing soon, I've asked Air Tight to loan me another cartridge for my Walker so I can do an exact comparison."

This plinth and the plinth Albert Porter designed for the Mk3 motor deck and the way they are constructed may well inspire any owner of an SP-10 Mk2 or Mk3 turntable. But certainly also those who want to make a beautiful base for their respective high grade turntables in order to gain excellent physical and frequency related sound properties.

Albert Porter is a reviewer for Positive Feedback Online. You can view Albert Porter's audio system there.

And you can visit his Albert Porter's Audio Website.

For comments you can reach him there per email:
Albert Porter.

Anyone who has a similar or different proposal for a plinth (eventually to be published on this page), is welcome to e-mail me too.

ALBERT PORTER'S BASE FOR MK-3

At left you see a different concept for a plinth. It is the Ebony plinth Albert Porter devised for his Technics SP-10 Mk3 motor deck.

The core of the plinth is a construction of thicker panels than in the original SP-10 Mk2 plinth. Shown here are the two Panzerholz sections bonded and milled plus basswood panel and 6061 aluminum plate. There is also the iron block and brass rod, but the iron block is not yet driilled or threaded.

Note that there are four circular filler inserts only for the MK3. They may be removed to accommodate the MK2 in the same same plinth. The inserts do not touch the Technics or outer plinth construction except by two stainless steel screws on each, which fasten to the Basswood panel in center. There are two brass mount rails with brass screws to mount the arm board.

Here is a rear view of Ebony plinth, showing split grommet + plate system for cables.

Albert Porter adds: I also designed a platform for my MK3 to rest on, it's 9 layers, including a layer of Texas Instruments FerriShield with dedicated ground plane. It's finished in Piano Black and is a mirror design of the MK3 plinth, with same angles, corners and shape.

You can read various posts on AudiogoN. Albert Porter tells about the quality achieved. He also relates about the cost of the total project.

FOR DUTCH AND FLEMISH READERS AND THOSE WHO HAVE SOME UNDERSTANDING OF THE DUTCH LANGUAGE:

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