SP-10 mkII, the next project

[Bon]

Originally Posted by user510

This seems logical but perhaps it might be useful to elaborate on the why's and hows of applying mass, stiffness and damping.

Mass: what does it do to help the stylus in the groove and where do you apply it?

My comments were concerned with the requirements of a turntable plinth system, although many of them would apply to the other important important electromechanical component, the loudspeaker, specifically the enclosure. A very good analogue for a simple vibrating system is the classical mass-spring-damper arrangement. Of course turntables and loudspeakers are a connection of vibrating components but it is useful to understand the behaviour of the simplest arrangement. Also to a great extent a vibrating system will have its behaviour determined by a dominant principal mode and understanding and controlling this mode is a key step in a satisfactory design. The equations of motion are determined by applying Newtons laws of motion, for circular and linear motion. Thankfully analysis of direct drive requirements is more straightforward than for drive systems where the motor is separate from the platter. For belt and idler drives, the system is an interconnection of two or more rotating systems about multiple axes of rotation.
Basically the requirement for plinth mass is in response to Newtons law that requires that every force has an equal and opposite reaction. In rotational terms, every torque has an equal and opposite reaction torque. Therefore a high torque direct drive like the SP10 mkII will tend to spin the plinth as motor torque is applied to the platter. The greater the plinth moment of inertia, the harder it is for the plinth to move even microscopically. Bear in mind the minute scale of the information the stylus is retrieving. I suppose there is a practical limit to the amount of inertia. The material stiffness is of consideration here because the plinth will have the frequency of its principal mode of vibration determined by the inertia and rotational stiffness (compliance). It would be desirable for this frequency to be away from frequencies of likely sources of extraneous excitation. In practice the choice of available plinth material limit the scope of choosing the principal mode frequency.

Originally Posted by user510

Stiffness: Getting back to that microscope pic of a diamond stylus reading the groove.... Any flexing in the plinth while the stylus traces the record groove is to be avoided because this will alter alignment geometry of the stylus/groove interface and also invite other disturbances such as micro-rocking of the platter out at the rim.

I would think that it is of utmost importance to provide a suitably rigid mechanical connection between the mounting of the tonearm and the mounting of the motor/platter.

Damping: This is where things get vague and wooly. The idea behind this is to reduce motor/bearing generated vibrations before they can reach the stylus/groove interface. Or to keep motor/bearing vibes from finding their way to the tonearm mounting.

The pages at Qualia Webs offer us some insight into the ultimate damping ability of various materials that have been tested there. Presumably the test is to drop a steel bearing ball from a specified height onto the test material. That test material has attached to it accelerometers which record the vibrations in the material that result from having had that bearing ball dropped onto it. This is really good information.......as far as it goes. But does it tell us everything we need to know about vibration damping in record player chassis design?

There needs to be testing using accelerometers and software that records the passage of these "real life" motor vibes through various materials. To track where these vibes actually travel. Can the vibes be conducted away from critical areas of the plinth and into areas designed to attract, hold and dissipate said vibes? I'd like to verify/quantify this. It would point us to more successful plinth designs.

I have empirically verified the Audio Qualia observations of the damping effectiveness of a resin structure. The problem is to include adequate stiffness. My best attempts so far is achieved with a layered construction of isopthalic polyester resin and cut glass fiber matting. This is laid down in a mold a few layers at a time and built up over days to the desired thickness. The curing of the resin generates heat and limits the laying up to only a few mm at a time

The SP10 mkII mold template includes the cut-outs for the turntable and armboard. This is my reasoning for the effectiveness of a layered construction: assuming a perfect DD motor system, and ignoring extraneous inputs, the plinth requirements are to resist torque reaction (mass) and to effectively damp whatever the inertia doesn’t soak up. Since in the idealized situation this rotational motion is in a horizontal plane, a horizontally layered plinth with suitable damping material between layers is very efficient at converting any motor induced horizontal torque motion of the plinth into heat by shearing of the horizontal damping layers. As an added benefit, such a ply structure has considerable transverse stiffness and therefore coupled with high mass, provides an excellent platform for mounting of a tonearm.

[johnsciolino]

Originally Posted by user510

What to do.......

Next step is to remove the motor unit and electronics boards, switches and strobe from the aluminum chassis and put the platter and motor into an alternate plinth of my own design. The electronics boards will go in another separate project box. The new design will accommodate 9 inch tonearms easily. In particular, I have a Graham 2.2 tonearm waiting for a decent enough record player to be matched up to. To go with the Graham I have an Ortofon MC Jubilee cartridge that mates well to it. So the idea is that a very accurately driven platter, that of the SP10 mkII, provides the drive for a tonearm and cartridge capable of very good detail extraction,... if a little short on dynamic slammy-ness. Perhaps the mutually analytic character of both the sp10 mkII drive and the Graham will combine to produce a spectacular result that looks way, way deep into the record groove and extracts the most minute detail in a chrystal clear holographic manner. Wouldn't that be something!


Updated Technics SP10 quartz PLL drive

http://www.edsstuff.org/dd_museum.pdf

Turntable Forum • Alternate SP-10 plinth design?

Put the Graham on this table.....
I have a supreme on my SP-15 and it is absolutely stunning

[user510]

There's an interesting thread on sp10 mkII bearing damage going on over at AudioKarma. Here's a link:

Bearing wear on an SP 10 mk II PICS - AudioKarma.org Home Audio Stereo Discussion Forums

[user510]

I've stalled out on this project because of....well.....caution. The bearing housing bottom cap. The part that houses a thrust ball bearing. This I assume is a threaded piece that screws onto the upper housing casting.
Here's a photo:


The red arrow points to the part I mean. Moderate unwinding force, using implements of destruction, will not budge the piece. Until I gather some more information on just what is involved in the attachment of this part to its mating part, I'm not going to proceed. These are the only parts I have. I can't afford to break any of it.

I'm "guessing" that it is indeed a threaded part and that there may be some thread sealant/thread locker applied to the threads from the factory. If this is the case, I'll probably resort to something like a strap wrench after getting some penetrant oil into the threaded joint overnight. Or so I think.

Anyone have any experience taking this part off?

tia,
-Steve

[vinylkid58]

Originally Posted by user510

I'm "guessing" that it is indeed a threaded part and that there may be some thread sealant/thread locker applied to the threads from the factory.

If there is thread locker applied to the threads, applying heat to it will break it down. Even moderate heat will help loosen the threads, but I'm guessing a lot of heat to this area of the motor housing wouldn't be a good idea.

The service manual doesn't show the motor housing in it's individual components. Figures.

jeff

[brianco]

The following url is interesting.

<http://www.vantageaudio.com/info/sp10acc.htm>

I have tried to contact Vantage but they can be difficult to contact at times be it by email or telephone.

They do brilliant restoration work and have sorted my SP10 with fully external electronics: although not yet completed, I saw the work just before completion and can say that I have not seen better.

[user510]

Originally Posted by vinylkid58

If there is thread locker applied to the threads, applying heat to it will break it down. Even moderate heat will help loosen the threads, but I'm guessing a lot of heat to this area of the motor housing wouldn't be a good idea.

The service manual doesn't show the motor housing in it's individual components. Figures.

jeff

I'm guessing that the material of the larger housing is die cast aluminum of the A316 variety with a tensile strength around 23ksi . Less than half the strength of a high carbon steel. Not very good elasticity. Somewhat brittle. It could suffer a stress failure with hand applied force.

Good idea about the use of heat....and not too much of it. On the other side of that casting is a circular rack of coils with some sort of clear coating applied. We wouldn't want to melt that coating.


-Steve

[user510]

Originally Posted by brianco

The following url is interesting.

<http://www.vantageaudio.com/info/sp10acc.htm>

I have tried to contact Vantage but they can be difficult to contact at times be it by email or telephone.

They do brilliant restoration work and have sorted my SP10 with fully external electronics: although not yet completed, I saw the work just before completion and can say that I have not seen better.

I can appreciate the sentiment, but...............not even tempted to go there. This is, after all, the DIY Audio forum. So I'm gonna do it here. But I do request some information on this one piece.

I have yet to see any photos of the insides of the bearing cap I refer to. So I guess that means not too many of us diy'ers have actually refurbished their own SP10 bearings.

Not good.

These SP10 bearings are showing wear just like those of any other turntable after 35 years use. This will be a very important part of the project to get back into 100% condition.

-Steve

[user510]

The following url is interesting.

<http://www.vantageaudio.com/info/sp10acc.htm>

I have tried to contact Vantage but they can be difficult to contact at times be it by email or telephone.

They do brilliant restoration work and have sorted my SP10 with fully external electronics: although not yet completed, I saw the work just before completion and can say that I have not seen better.

I can appreciate the sentiment, but...............not even tempted to go there. This is, after all, the DIY Audio forum. So I'm gonna do it here. And....................I just figured it out.
Here's where I'm at now:




The photos do indicate a generous amount of thread sealant/locker. I used a heat gun to warm that up. The rest of the casting did not heat up.

I installed the lower motor casing back into the chassis to increase the leverage when I applied a turning force using the strap wrench I just bought.

Right Hand threads. The cap unscrewed smoothly but with quite a bit of drag from the goo stuck in the threads.

I suppose it will be a good idea to re-assemble with same/similar sealant/locker.

Victory

-Steve

[vinylkid58]

Originally Posted by user510

I suppose it will be a good idea to re-assemble with same/similar sealant/locker.

Yes, Loctite 242 Blue Threadlocker should do just fine. Just clean off as much of the old stuff as you can before re-assembly.

Loctite Threadlocker Blue 242 from Loctite Adhesives

jeff