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hobbyists's
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Page created and first published March, 2002

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Technics SL1000 Mk2 in all its glory:
SP-10 Mk2 turntable, SH-10E Power Supply, SH-10 B3 Obsidian Base,
EPA-100 Tonearm and Remote Control SH-10R. |
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Technics
SP 10 Mk3 Motor Unit with SME 312S (Magnesium), and Air Tight PC1 Moving
Coil cartridge in Albert Porter's Panzerholz/Ebony Base.
Image Courtesy Albert Porter. |
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DIRECT DRIVE There exists
another method of achieving accurate reading of the record's signal. That
method is letting the platter rest directly on the motor shaft. In fact
the shaft of the motor is the spindle of the platter. The platter is in
place of the pulley. In this case a heavy motor is necessary as the platter
is directly connected to it. The strength of the motor (its accuracy and
its torque) can be used completely while eliminating any transmission
by intermediate parts. Since motors do not turn smoothly but rotate in
steps (the more poles the smoother the rotation), the turning has to be
regulated electronically, has to be smoothed out, in order to achieve
a continuous and even turning. |
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FIRST DIRECT DRIVE PATENT Thorens developed a direct drive motor way back in the nineteen twenties. Thorens applied for a patent for this direct drive turntable motor, tourne disque in French. On the document is written: "TD à commande directe". It was issued by the "Bureau fédéral de la propriété intellectuelle" (Federal Office of Intellectual Ownership) in Switzerland, on June 21, 1929 and was described in the "Exposé d'Invention". Thorens however refused to use a direct drive motor in the music lover's turntables. At the time the technique was probably too expensive to make it work to perfection. Thorens applied the direct drive technique in the nineteen seventies in their studio turntable. And so did EMT. It was their answer to the success of the Technics direct drive turntables, especially the SP-10 mk2 turntable. |
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EARLY SP-10 In 1970 National Panasonic (Technics) had introduced the SP10 direct drive turntable. It was a single unit with no separate power supply. Its speed was regulated by reading the minute fluctuations of the platter with a tachometer and so fluctuations in the turning of the motor could be corrected. |
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ON A WOODEN BASE The player had two speeds: 33 1/3 and 45 rpm. These were adjustable. The pitch control had a margin of +/- 2%. Wow and flutter measured 0.03 %. Rumble values were -50 (DIN A) and -70 dB (DIN B). The weight of the platter was 6 lbs., appr. 2.720 kg. A wooden base plus acrylic cover were available as extras. |
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SL 1100 Later
on other tables like the SL-110 and the SL120 were introduced which worked
along the same principle. |
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TECHNICS CATALOG LP A tool in the clever marketing by Matsushita/Technics/ Panasonic of their direct drive turntables was the release of a special Technics Demonstration Lp in a gatefold cover picturing the range of DD turntables: SP-10Mk2 (SL1000), SL-1100, SL-120, 1300, 1400, 1500, 1800, etc. At left the Dutch edition. I am not sure if this was a typical Dutch affair. |
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SP-10 Mk 2 In 1975 the SP-10 mk2 (together with its Power Supply SH-10E) was introduced. It was a great step forward if compared to the technique of the Mk1 and other DD-turntables. The functioning of the Mk2 was quite different. Now -to put it simply- the motor was turning at a given speed which was steered by a set frequency which was generated by a quartz crystal. Hence the turntable's performance is not affected by any altering in the frequency of the mains nor any voltage fluctuation. A fluctuation in speed is instantly corrected by the motor itself without the use of a tachometer or a playback head which reads the magnetic imprints on the inside of the platter (a method Denon used in their DD turntables). This meant a mere perfect performance as far as speed accuracy, wow and flutter are concerned. In order to avoid fluctuations from temperature and those caused by mechanical parts no speed adjustment facility (variable pitch) was incorporated. This was a drawback for people with perfect pitch and for those music lovers who wanted to play a variety of old shellac records which are not always cut at 78 RPM. A new and unique feature of the SP 10 MkII was the incorporation of a mechanical and electronic brake not encountered on other DD turntables, not even the SP10MKI. It reminded of the direct start of the EMT turntables and the clutch of the Thorens TD-124 and it made the SP-10 Mk2 a true Studio Turntable. Many radio stations installed the Mk2 for playing 33.33 and 45 rpm discs for the broadcast of music programs. By increasing
the capabilities of the motor and designing refined and complex electronics
to regulate the motor's rotation (for smoothing out the shocks when moving
from one pole to the next) the SP10mk2 attained its practically incomparable
specifications. Instead of the soft mat which was used on the earliest SP10 (SL1000) and SP110 (SL1100) now a hard mat adorned the heavy platter. The hardness is not without significance for the sound performance which is an essential feature of the SP10Mk2. It goes without saying that an Mk2 or Mk3 is practically worthless without the appropriate power supply (SH-10E). A power supply is hard to find separately. And if only the motor is offered in an auction you will never be sure to find a separate power supply unit (PSU) and you will not be able to play records with your SP 10. For an expert it would be possible to build a power supply as in the Service Manual all circuits and values of components are given. The platter
of the SP-10 mkii weighs 2.9 kg / 6.4 lb. To prevent a turntable platter
from sounding like a bell, the inside has to be covered with a sound absorbing
material. This can be a layer of a resin like substance as with the early
Melco turntables or - as in the case of the Technics SP 10 mkii - with
a relatively thick bituminous sheet. Of course not in the middle part
which is connected to the motor section. |
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SONY PS-X9 There are other high quality direct drive turntables: the Kenwood Kenwood L-07, and the Denon DP-65, 75 and 80 are well known. Denon and also Sony came up with specific studio turntables: PS-X9 and DP-100M respectively. These are complete systems, tonerarm included. Not only the price but surely the design may have been the reason that the DP-100M and the PS-X9 were less popular among audiophiles and serious music lovers who like to add a tone arm of their choice. |
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DENON - NIPPON COLUMBIA - DP-100M While
the Technics SP-10 and the Denon DP-65, 75 and 80, can be mounted on
any sort of plinth and can be combined with a variety of tone arms,
the Kenwood came with its own arm and there was a possibility to mount
a second arm. Although the Technics SP-10mk2 and Mk3 are considered
as studio turntables, Nevertheless audio magazine 'La Nouvelle Revue
de Son' in France awarded the DP-100M their "Decibel of Honor"
(Décibel D'Honneur). |
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The Denon DP-100M uses a split platter to minimize rumble. The rumble value is -90 dB which is an credible achievement. It is not advised to use a different turntable mat on the DP-100 (if this would be possible at all), as a different mat will influence the signal to noise ratio in a negative way. A spindle weight can of course be used. |
The DP-100 boast of a very strong and heavy motor which is used in quality cutting lathes. Wow and flutter is also excellent: 0.003 %. The heavy chassis and motor rest on appropriate springs in order to isolate the chassis and platter from the environment: mechanical feedback is practically non existent. |
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When taking off the top platter, the basic platter is revealed. The two holes are there to lift this basic platter from the spindle. The basic platter is designed in such a way that there is a second rim underneath which has a fine magnetic pattern on the inside |
The magnetic pattern on the inside of the platter is read by a recording head as used in tape recorders. The recorded signal is compared instantly with the frequency of the quartz crystal in the electronic circuitry for steering the motor. The smallest deviation is recorded and corrected. |
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SP 10 Mk III Technics went even a step further in designing the perfect turntable. In 1981 the SP-10 Mk 3 was introduced. It had a platter consisting of a copper alloy inner section and an aluminum outer part, weighing a mere 10 kg = 22 lb. and the complex electronic circuitry to regulate the speeds and constancy of the rotation of this heavy platter. The total unit itself weighs 18 kg (=40 lbs). This machine was not sold in great quantities because digital media were emerging on the horizon and few owners of an SP-10 mk2 saw the need of switching to this newer version of turntable. In hindsight they may regret it. VARIABLE SPEED The advantage
of the Mk3 is not only the practically unmeasurable wow and flutter, but
the fact that now all speeds can be adjusted in 0.1% steps to +/-9 % which
makes this unit ideal, also for transfers of all records including all
sorts of shellac records. Note: if you look carefully you can see that
the SP-10 Mk3 has a softer turntable mat (at least in the picture) compared
to the mat on the SP10Mk2 which is harder. PRICES Stereo Buyers' Guide from 1989 still lists both SP-10mk2 and Mk3 turntables. Prices were then:
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SHIPPING BRACKET Note: If the motor unit of an SP10, SP10mk2 or SP10Mk3 is being transported, instructions in the owner's manual have to be followed carefully. In case of the Mk2, the motor has to be secured with the original metal clamp which should be fixed with three screws to the disc of the motor and with four screws to the chassis. This in order to avoid damage caused by shock. If the clamp is not available, a clamp should be borrowed or made by you. The omission of a clamp can damage the motor and the spindle and impair its accuracy. Many prospective buyers and also owners of the SP10Mk2 have asked for details of the special clamp which is necessary if the turntable has to be transported. If your SP-10Mkii does not have this clamp, you can make this shipping bracket yourself or have it made in a machine shop. It is a simple piece cut out of a thin sheet of metal. Aluminum of 2 mm thickness will be OK also. Thinner sheets may bend though. The template can be ordered. See at the end of this page. |
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ORIGINAL SCREWS OF MK2 In some cases the original screws of an SP-10 MKii are lost and have been replaced. At left the original screws. The fixed, brass cylinders take care of precise positioning of the platter. No deviation is allowed. |
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CLOSED MOTOR The MkII has a completely closed motor, similar to the SL1100. The relatively large disc which is the top of the motor supports the platter. In addition to the eletronic brake there is an adjustable belt which helps break the motor/platter combination mechanically. Belt and the adjustment facility are hidden under a plate which surrounds the motor/disc so dust is kept out. |
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OPEN MOTOR The newer generation of Technics turntables introduced at the end of the nineteen seventies/beginning of the nineteen eighties do no longer have a closed motor compartment. Now the stator with the green coils (core) is solid with the plinth/chassis. The bearing housing of the spindle is fixed in the center. The supporting disc on top of the spindle is actually very small. This "simpler" method of construction was applied in the Technics SP-10Mk3 design and later found in the cheaper models like SL 1810 and SL 1310, the 10 referring to the SP-10. |
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HEAVY PLATTER At left the underside of the heavy platter. Much of the weight is of the large ring with magnets: the rotor. The mass is not concentrated at the periphery of the platter as would be the case with heavy belt drive designs. Not in the SP-10 Mk3 because that would slow the starting and stopping time of the platter. It is obvious that care has to be taken to prevent dust to settle in the stator and rotor. Check and clean with compressed air from a can (Dust-Off) or use a hair blower set to cold. Then you can put the platter back again. The turntable has a starting torque of 16kg/cm-2, nearly three times the value of the SP-10 mk2. The rotor and stator of the SL 1810 (shown below) are of course less sturdy and quite small if compared to the large and heavy rotor and stator of the magnificent SP-10 Mkiii. The electronics of the simpler turntable match of course this small motor with light platter and do not differ much from the design of the later SP-15 and SP-25. |
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WARNING Since the platter is part of the motor, all 10-models do carry an important warning. At left the one on the SL-1810 turntable. 1. The turntable platter of this set is part of the motor assembly. Therefore do not remove the tunrtable platter unnessarily. 2. Do not connect the AC power plug when the turntable platter is removed. This may cause power supply problems. 3. Never let dusts or iron fillings come in contact with the rotor magnet. 4. If lubrication becomes necessary after approximately 2,000 hours of playing, remove the turntable platter and apply 2 or 3 drops of the enclosed special oil to the top of the bearing. |
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HANDLE WITH CARE The
platter of the Mk3 consists of an aluminum base topped by a copper platter.
The aluminum platter connects directly to the spindle. |
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You need two handles for carefully lifting the heavy platter. Pictures of the Mk3, rotor, stator and platter with handles courtesy photographer Albert Porter. |
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VOLCANIC GLASS The technicians of Technics designed a special base for the SP10 mk2 which was also used for the SP10 mk3. It was made of obsidian (volcanic glass) which had a nice shape and was beautifully polished. Hi-Fi Choice from Great Britain however reported that the bass was somewhat slender and that there was some shallowness in the mid and upper mid frequency region. This is certainly caused by the amorphous "structure" of volcanic glass. Glass sometimes used for plinths and platters has this characteristic.
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EPA 100: DAMPED TITANIUM TONE ARM They also
designed a special arm to match the new SP10MkII by using a very innovative
damping mechanism with an oil reservoir inside its counterweight, and
by applying the then new space age material titanium: EPA 100 (1976).
The titanium arm tube and the damping of the counterweight by means of
an oil reservoir in the weight made the signal very precise and clean.
Also the head shell contributed also to that much controlled signal. The
sound with the EPA 100 ia somwhat les chiseled and vigorous, but rather
dull. That was not always to the liking of audiophiles. |
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EPA 500: INTERCHANGEABLE WANDS Technics
introduced a tone arm with an even more revolutionary design: EPA 500
(1979) with various arm tubes for use of a variety of cartridges from
low to extremely high compliance. Paarantly inspired by the SME Series
III from 1978. |
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Because of the high torque the platter of both SP10mkII and mkIII starts within a fraction of a second. There is an electronic and mechanical stop. When the platter is not spinning it is mechanically locked, hence the SP10 is not suitable for scratching even if the mechanical brake has been disabled (which can be done). The time of mechanical braking (the speed) can be adjusted to one's own needs. If you want to use this quick start and stop capabilities while the diamond tip is in the groove, a heavy base is imperative. 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:
Better
not use corian as it has a frequency curve with emphasis on high frequencies.
The properties of corian are also not always as desired because the percentages
of aluminum varies. |
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A SOLID BASE There are
many solutions on how to build a plinth for the SP-10Mk2 and Mk3. You
can find several proposals with drawings and pictures on the www.
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If you are - like I am - a lover of classical music and jazz and like to play at very realistic sound levels through relatively big loudspeaker systems connected to quality amplifiers, then you need to eliminate mechanical and acoustic feedback. In that case you should build a different plinth in which you use springs instead of rubber feet and de-couple the SP10mk2 from its surrounding to the max.
I let myself be inspired by Cotter's design, though the article did not give too much insight into the details of the construction. So I did not strip the turntable as Mitch Cotter did, but kept it intact and made my own design for a base. I also did not use the special layered base plate but two layers of chipboard glued together.
The base plate rests on 3 springs. The positions of the springs can be determined empirically by shifting the positions in relation to the total weight of the base plate with motor unit. My construction makes it easy to lift the rectangular box (side panels) in order to position the springs and find the best position in relation to the weight, to adjust the height of the springs, to determine the damping of the springs and to connect a cable to the tonearm.
The box is not fixed to any part but rests on top of the beams fixed to the bottom plate. For the mounting of the arm I used a sandwiched board of acrylic 4 mm thick covered on both sides with 1 mm thick aluminum.
In my construction the base plate's measurements are: 58 cm (W) x 44 cm (D). Two 18 mm chipboard panels with a black veneer coating (plastic) are glued together.
The bottom of the construction consists again of 2 layers of chipboard, but now the plain kind.
On the 4 sides I have glued (and screwed from underneath) 4 pieces of wood of 4 x 7 cm. They are positioned at a distance of 10 mm from the periphery of the bottom plate.
On the inside of the side panels I have glued 4 pieces of wood of 10 mm x 10 mm at such a height that they will rest on the 2 layers of chipboard and disguise the bottom.
The measurements of the bottom plate are 60 cm (W) x 54 cm (D). Height of the box (side panels) depends on the height of the springs used when they are pressed down by the weight of the unit on its base plate (including the weight of the platter and arm).
In
the drawing below the amount of foam
to be inserted inside |
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I
can supply the following manuals and the template for the SP10 |
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© Rudolf A. Bruil - Page created and first published March, 2002 Home
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