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, 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.

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 Kaneta version the SP-10 is stripped. 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 sheets of wood, 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 chipboard
• 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), and - 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 as a 5 mm thick turntable mat shaped according the drawing on the this page. 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" pressed and bonded together.
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 characteristic without abrupt filtering of the signal, so that 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. Used in alternate layers, they teem up very well for arm boards and chassis, whereas acrylic alone gives less definition and detail.
The frequency of the isolating rubber feet or springs supporting the base plate (the SP10mk2 unit included) should preferably be between 2 and 4 Hz.

ALBERT PORTER'S 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 armboard and the room the tonearm base needs. The armboard has about the same thicknes as the top panel of plywood. The armboard 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, of whatever is generally used for coupling such an important component as a precision turntable. Albert states: "There is no need for suspension with this Technics as there is no feedback problem. The plinth as shown weighs 85 pounds and sits in my equipment and software bookcase on 2.5" Maple butcher block shelf, approximately 20 feet 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 comparisons."

This plinth and how it is constructed is without no doubt a design which may well inspire the owner of an SP-10 Mk2 or Mk3 turntable. But certainly also those who want to make a beautiful base for their respective 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 and his website.

For comments you can reach him there.

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

 

Additional info:

Cotter's original idea of the floating chassis is of course that the chassis rests or hangs on springs. So he came up with the Acoustic Research tunrtable, the first in the world with a floating (suspended) chassis. The drive belt in this construction acts as a spring as well.
In principle all turntables on springs (direct drive tts and belt driven tts) can be considered as subschassis turntables, although direct drive turntables cannot comply with this principle for one hundred percent because they lack the rubber drive belt.
If you want to apply the Cotter principle To find the appropriate springs one needs to calculate what the strength of the springs should be.
It is possible to do it by trial and error and find springs that could be used. Once springs are found that come close to the ideal, one can of course adjust their functioning by making the unit + board lighter or heavier. And in this way the best frequency can be found without loosing speed stability.

Mitch Cotter asked the factory to calculate exactly what sort of springs he would need: thickness of material, number of turns, height, shape (clock) and the amount of torsion. All in relation to the total weight of the SP10 plus the base plate it will be mounted on.
That is what I did for my first 40 kg. turntable in 1980. I had ordered the springs from a factory and they were made in accordance to the total weight of the turntable. The plinth was a box made of serpentino (stone) and filled with sand. They made 4 springs for me and they worked well. It is all very technical. The cheapest method is the empirical method. But for that you need free access to a spring shop where you can browse through all the boxes with all sorts of different springs.
Emperical means that you would need to bring the SP10 plus the base you have chosen to the shop. Better would be to take a heavy board the size of the future base plate plus some exra weights to the shop and try the springs you have found.

The springs have to be sturdy in relation to the total weight of unit plus chipboards. They also have to be damped with plastic foam. The sturdiness is important, because if the springs are too supple, the unit will not show its speed accuracy. Too much plastic foam will make the sound dead. This construction makes it really possible to tune and achieve the desired reproduction.
You may have difficulty in finding the right springs and the best damping of the springs. Before you will make a very elaborate plinth and box around it, maybe you should just place motor mounted on the plate on the springs you found and listen carefully. And if you have the idea that this is the way to go, you can continue the project. You can shift the springs to other positions in order to have the best distribution of the weight.
If the system is not level, you can put one or more round pieces of plastic or cardboard underneath one or more springs. The ideal would be of course that, if you push with your index finger on the spindle, that then the whole unit would evenly go up and down as described on the turntable adjustment page.
If the trial of the simple set up shows quality, then you could make a definitive version of your floating SP10 with a handsome cabinet around it and couple it by means of rubber feet or use metal cones underneath that cabinet. These are just suggestions. Remember: never be in a hurry but take time to find the most musical solution. Good luck.BACK

BACK TO THE SP-10 PAGE