TECHNICS SP-10MkII turntable – Pt 2

The Technics SP-10MkII turntable’s platter (yellow) is 2.9kg cast aluminium and is screw-fixed down onto the sub-platter rotor of the Direct Drive motor.

A ring magnet (red) is attached to the inside of the rotor.  The motor stator coils are fixed onto the motor bearing base below (green).  This bearing base is also cast aluminium and is attached to the turntable top chassis frame (green), with 4 small M4 screws.

If you examine the Technics SP-10 in detail like this, you can see that there are things that can be improved for potentially better performance.

SP-10-x-sect-310119colour CC

(All images can be re-used under the Creative Commons (CC) licence BY-NC-SA – Owen Young)

The SP-10 bearing shaft is only 7.13mm diameter, which looks quite small for a turntable with a powerful motor.  However, unlike belt-drive or idler/rim drive turntables, the SP-10’s Direct Drive, balanced platter does not apply side forces to the bearing.  So Technics obviously thought that this skinny bearing was adequate.

The bearing design appears conventional with brass sleeve & steel ball at the bottom, supporting the shaft end.  The bearing shaft bottom is fitted with a plastic ‘thrust pad’.  The steel ball does not turn, it is captive-pressed into the end of the brass sleeve by the screw-on bottom cap (below).

IMG_9902

Motor bearing cap underneath.

Bearing lubrication:
According to KAB USA the Technics SFWO 010 oil specified for its DD TTs is Anderol 465, a SAE30 grade synthetic oil.  KAB sell it inexpensively, but I will use a locally available low-temp grade Mobil 1 5w-30 synthetic engine oil – which has similar low temp viscosity.  (Yes, the Mobil oil will have engine additives, but these will be inconsequential in a room temperature, slow running turntable bearing.)

Technics specify that 2-3 drops should be squirted into the hole adjacent to the sub-platter spindle (see above) every 2000 running hours (that’s not much, every few years).  This means that the oil ends up in the shallow ‘well’ formed around the top of the motor bearing sleeve (below) and then can slowly seep down to lubricate the sleeve & bearing shaft.  In other words, the sleeve (and ball) does not need to be pre-filled with oil.

IMG_0273 a

Sub-platter magnet rotor with lubrication hole (arrowed).

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Motor stator with oil ‘well’ around the bearing sleeve (arrowed).

Rotational torque:
The Direct Drive motor has high torque & the PLL speed control/correction circuitry is constantly adjusting rotational speed – albeit only micro-adjustments, but we know that even minute stylus ‘drag’ forces do affect reproduced sound.

The SP-10 chassis plate uses 5 x M5 machine screws for attaching the SP-10 to a cabinet or ‘plinth’.  However, these necessarily go through oversize holes in the cabinet-plinth and so rotational rigidity relies mainly on the ‘friction’ grip between the SP-10 aluminium chassis & the cabinet-plinth top.  Rotational stability is most important with a Direct Drive motor and I think that we can improve the SP-10’s rotational rigidity with improved fixings.

Some of the things that could be improved:

  • Improved or additional fixing of the turntable top chassis to its new ‘plinth’ for better rotational rigidity.
  • Damp the SP-10 top chassis.  This is a complexly ribbed casting.  Surprisingly however, it ‘rings’ (500-1000Hz) when tapped.
  • Damp (or remove) the cast alloy bottom cover (eg with self adhesive butyl, Dynamat or similar material).  This is heavily paint coated, but it too, resonates.
  • Damp the motor bearing base (photo above).
  • Damp the Sub-platter magnet rotor.  The ring magnet baseplate is thin sheet steel, attached to the Sub-platter with only 3 screws.
  • Add an Albert Porter style ‘noise-sink’ connected to the main bearing bottom thrust plate.  Properly designed, this can also greatly improve structural support for the whole suspended SP-10 chassis.

New plinth design:

2 tonearms can be accommodated – 10″, 12″ and even 9″ tonearms can be fitted.

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SP-10 mock-up with 12″ and 10″ tonearms.

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My plinth concept is a rotationally-rigid, lightweight plywood plinth.  Mass will be added to absorb micro-vibrations from motor ‘cogging’, but this mass will be located at the bottom of the plinth, for stability and away from the record-stylus.

I hope that this will preserve micro-information, harmonic detail, dynamic leading edges – ie. ‘musicality’.

A heavy baseplate (stainless steel, 9kg approximately) will also provide a ‘sink’ for any motor vibration or bearing ‘noise’.

Plinth-concept-section 3

Early concept sketch.

The internal shaping of the plinth (using CNC machining) will maximise rotational strength and minimise mass.

The finished plinth will be supported on mag-lev (magnet levitated) ‘feet’.  (I had good results using mag-lev feet on the rim-drive Transfi Salvation turntable.)

010219-layer-17.5

SP10-x-Sect-050419

Next time – Technics SP-10MkII – Pt 3:  Plinth construction.

See also – Technics SP-10 MkII – Pt.1

2 thoughts on “TECHNICS SP-10MkII turntable – Pt 2

  1. Pingback: My music system | D a r k L a n t e r n

  2. Pingback: TECHNICS SP-10MKII turntable – Pt 3 new plinth construction | D a r k L a n t e r n

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