New acrylic platter for the SL-1200/1210

[FunkArt]

With the platter still in prototype form, I had wanted to leave commenting till much closer to release but sufficient has been written encouraging an early response.

“Direct drive “turntables””.
“Paramagnetism(?)” (as opposed to diamegnetism, as opposed to ferromagnetism).
Lexan (polycarbonate) vs acrylic.
Flux leakage.
These and more have been introduced as potentially problematic.
The following thoughts are intended to help.

Let’s start with the DD turntable: This is but a motor with its attached load - we might call it a platter, (plastic, aluminium etc.) but it is just a load.

Now, at below £500 lest we forget, SL1200 was built to a price. People buy it because it is a value-for-money entry product.
it succeeds only because the size of its highly refined motor permits a high torque. This is SL1200’s true claim to fame.

Why entry product? For high end use its other features are mediocre - else why the need for a new arm, platter, isolation and so on?
Once upgraded, however, there is no doubting SL1200’s renewed capabilities but then all that’s left of the original is the motor!
But even the execution of the motor is left wanting…

Motor Design:
For a motor to work, there must be an associated magnetic field [sic].
SL1200’s drive coils are all but totally enclosed in the magnet’s rotor, with virtually no leakage. So, no adverse effects result from them.
Eddy currents: These occur only in metals subjected to a varying magnetic field.
SL1200’s platter and rotor magnet are one - they turn together - thus, no eddy currents are generated in the platter.

If a motor is shielded, then it is shielded. End of discussion.
If, however, a motor is unshielded, its magnetic field spreads out. SL1200’s rotor is not fully shielded; flux leakage is defacto.
Aluminium (“paramagnetic” or otherwise), can’t shield magnetic fields, which are actually detected through the platter at the record. This holds equally for copper.
We plot and measure field strength using Hall sensors but few of us have those in our kitchen drawers. Still, this field is high enough for a simple child’s compass to detect! Now, this is something you can all try with your aluminium platters.
It gets worse. The alternating poles of the rotor’s magnet produces an alternating field. This is close to the end of side but its interaction with cartridges is not easy to predict given different cartridge sensitivities and designs. What is certain is that this not what we want from a high end product. It must be dealt with accordingly.
This is one reason (of two) why using just a mat is not a full solution. Needless to say, eliminating this was part of the design brief.
(Given the nature of the problem, (we didn’t design the motor) it is churlish to regard this as a case of shutting the stable door after the horse has bolted. Still, given the era SL1200 was developed it was a masterful piece of engineering. Respek.)

To recap: As the platter moves with the magnet, there is no mechanism for eddy currents to be generated; so it matters little if the platter is aluminium, acrylic or Swiss cheese (Everyone knows Swiss cheese makes poor magnets).
Flux does, however, escape from rotor’s magnet. Unshielded it induces voltages in the sensitive generator of cartridges, requiring of a solution.

Platter material choice:
Both Lexan and acrylic have indeed been considered with Lexan pushing up the price considerably.
“But we are not price sensitive, here. Surely it is performance that matters?” I hear you ask. (Not price sensitive? Hmmm)
“Subtle but important”, (as quoted), Lexan may better acrylic but
under test, where our tests went further and ignoring Lexan’s elevated price, we concluded that adding (the modestly priced) Achromat improved on Lexan. (As we believed it ought to).
Why go all out to screw punters with a more expensive platter that could then itself be further improved?
Made no sense to us. We stuck with acrylic.
(Save the difference towards our arm and get yet more improvement!)

In conclusion, the raison d’etre of our platter:
- To produce a more stable platform mechanically than SL1200’s original offering, which rings.
Well, our one does not ring. ✔

- To eliminate any flux leakage that might otherwise interfere with the cartridge’s function.
Well our compass no longer moves. ✔

- 1200’s have excellent overshoot characteristics. We retained this by optimising various of the platter’s dimensions to match the inertial load, motor power and servo. (Increase mass / inertia willy nilly and stability is adversely affected. It’ll work but not as designed.)
If this is a bit techy, you’ll just have to trust us. ✔

- To produce an overall improvement in performance for a reasonable price given all the various and conflicting demands.
Any high end deck+ arm will set you back £5-15k. Fully laden mods are less than £3k. And the results…
The proof is in the listening. ✔


Simples. Bzchuz

Well, back to work.

Arthur

[MCRU]

5 posts in 3+ years, well the above was certainly worth waiting for!

Nice write up kind sir.

[chris@panteg]

Thanks for talking the time out to explain , Arthur ! I think a few question's have been answered .

[Marco]

Most interesting, Arthur. I thought you may have had a plan up your sleeve

Let's see what Mike has to say in response....

For me, though, it's very simple: all the technical postulating in the world means next to bugger all to potential customers (audio enthusiasts) who will buy the product. With hi-fi equipment and ancillaries, the proof of the pudding is always in the listening, so when I receive an acrylic platter to test against Mike's, we shall let 'battle' commence!

Look out folks for an exclusive in-depth review soon!

Marco.

[FunkArt]

I couldn't agree more about listening proof being the final arbiter.

Where I'm at really isn't a case of technical high falootedness(?), it is simply being transparent in stating the design process whereby a product starts it journey to reach the real world market.

Designers have preferred routes to a given goal and they should all be respected, all the more once one understands reasons for choices, sometimes difficult, sometimes not always clear that have to be made.

It is a matter of confidence that you the listener are being treated with respect.

In thanking you for your comments, I'm sorry that I find it so difficult to engage more. It's not personal!

Dog walkie time...

Arthur

[Marco]

Designers have preferred routes to a given goal and they should all be respected, all the more once one understands reasons for choices, sometimes difficult, sometimes not always clear that have to be made.

I absolutely agree, Arthur. If I were to predict anything about the forthcoming comparison between both platters, it would be that neither is likely to be 'superior' overall. However, we shall see.

My suspicion though is that this modification will be subject to achieving synergy with the existing ancillary items on a modified SL-1200/1210, the same as any others to date, and in that respect, choice for each individual will depend on a number of factors. And choice is indeed good!

It is, after all, about marrying the respective sonic signatures of the component parts of the turntable, in order to create a 'musical whole', which is precisely how I build not only my version of a modified Techy, but also my whole system - and therefore there are many variables to consider

As I'm sure you'll agree, one must look at modifying the Technics in terms of creating a system, and not merely a collection of disparate parts.

There is one key variable, however, I feel which could heavily influence the outcome of comparisons between platters, and that is which off-board power supply the respective T/Ts being tested are using. In my experience, upgrading the existing PSU on an SL-1200/1210 has the single most significant impact on its sonic performance, closely followed by the bearing and platter, as essentially all heavily influence the behaviour of the drive system.

As you know, there are now quite a few different off-board PSUs on the market for the Technics, all of which will impose their own 'character' on the final sound (or cause the T/T to 'behave' in a certain way, sonically) - and it is the success of this 'relationship' between the PSU and chosen platter, symbiotic or otherwise, that I feel will be highly significant, not to mention the effect of the bearings used (depending on their design), which will also be very influential.

There are, as far as I know, four types of bearing currently to choose from: the stock Technics one, the Timestep one, the Vantage Audio one, and Mike New's - all of which to varying degrees impose their mechanical influence on the sonic performance of the T/T.

A holistic™ approach (descriptive term copyright of Dave Cawley ), as ever, will be key to achieving the desired result, and with it, superlative sonic performance.

In that respect, may I ask which PSU and bearing were used on your sample T/T to carry out the preliminary tests with the new acrylic platter?

Marco.

[etphonehome]

This thread has been a truly interesting read and am thankful to both Mike and Arthur for their contributions explaining the magnetic flux from the Techie motor.

Out of curiosity, I decided to do a simple test with my simple compass.

I took off the MN platter, and held the compass near the motor coil, and when I pressed on the start button, the needle moved and pointed straight at the direction of the coil. Did this a few times and the results were the same.

Then I placed the MN Platter on and did the same, and held the compass at the same position. The needle stayed put.

Now, of course this is a simple crude test at best with a not so sensitive compass...but the platter seems to provide some shielding. How much shielding, I can't say. Will leave it to the experts to do the testing.

[FunkArt]

In that respect, may I ask which PSU and bearing were used on your sample T/T to carry out the preliminary tests with the new acrylic platter?

Ah. You do like your cans of worms. Well, Marco, from what you have said regarding the importance of the various offerings, it is important to us that what we have is as universal as possible to the majority of readers.

So for simplicity (and consistency) we most often use a standard Techy. Little point talking about something that the vast majority of people do not have (at this stage) and so cannot relate to.

That is not to say that for our own in-house R&D we don't test various other options.
Equally for interest sake it is not too surprising that for example we use FXR in not one but two guises, Rega based and also Techy based. But then we also use more conventional arms, to check for applicability.

There are also other items currently in experimental stage which further extends our overall test procedure but these I can't divulge.

People have commented that it is "only an acrylic platter". Truth be told, this "simple" platter is proving a veritable project in its own right and here's why:
A case in point is the critical central sensor (which comes with the platter). Production of this one apparently straightforward looking component alone comprises some 13 parts and two jigs.

Then there is the testing and measuring parameters of the shield. All necessary iterations in getting it to work invisibly.

It is for all these reasons that although word is out and prototypes have had their initial airing, we are not rushing them out of the door and instead still quoting some 8-10 weeks to production release.

At the end of the day, if, as Marco says, the proof is in the listening and you do end up liking it, there has to be a reason. I'd like to think that all these hours of physics and development played some little part, as they have with other products I have had a hand in creating.

Cheers.

Arthur

[Mike_New]

Well I guess I should respond to the observations of Arthur in hopefully a non controversial way.

Firstly he discuses the general commercial aspects of the ubiquitous SL1200 series of TTs; which has been well covered and discussed in many posts on this forum and many others. He then goes on at long length to talk about the motor design. Non of which I have any argument with. Excepting that it is interesting to note and I quote:

“If, however, a motor is unshielded, its magnetic field spreads out. SL1200’s rotor is not fully shielded; flux leakage is defacto.”
He then goes on to say, and I quote:

“Aluminium (“paramagnetic” or otherwise), can’t shield magnetic fields, which are actually detected through the platter at the record. This holds equally for copper.
We plot and measure field strength using Hall sensors but few of us have those in our kitchen drawers. Still, this field is high enough for a simple child’s compass to detect! Now, this is something you can all try with your aluminium platters.”

A compass does indeed detect magnetic fields.
And it might be possible to see a deflection when placed on a Solid Copper Bonded Alluminium Platter (I have not tried this yet, I lost my play compass a long time ago) But, then try doing the same thing on an Acrylic platter that does not have some form of shielding attached to it, and see the difference!!!!!!!

You say
“The alternating poles of the rotor’s magnet produces an alternating field. This is close to the end of side but its interaction with cartridges is not easy to predict given different cartridge sensitivities and designs. What is certain is that this not what we want from a high end product. It must be dealt with accordingly”

I would like to clarify the wording here, I believe what Arthur means here is that the flux radiates from the outer edge of the rotor torus. Which is correct, I have plotted it.
Further I would like to mention that the flux intensity like all electromagnetic radiation, is proportional to D^2
Where D is the point distance from the source.
So the real effects of stray flux, will be observed towards the centre of the platter.
It is interesting that Technics, in their infinite wisdom did not make the rotor magnet any larger in diameter that the size of the record label. Maybe they knew something!

Accordingly I ask how does he intend to deal with it??????

Referring to the motor he states:

“Still, given the era SL1200 was developed it was a masterful piece of engineering. Respek.)” (sic)

I agree with him, as I have said on a number of occasions.

His final statement is as follows:

“To recap: As the platter moves with the magnet, there is no mechanism for eddy currents to be generated; so it matters little if the platter is aluminium, acrylic or Swiss cheese (Everyone knows Swiss cheese makes poor magnets). (I personally love a lump of Swiss cheese with a good red) Flux does, however, escape from rotor’s magnet. Unshielded it induces voltages in the sensitive generator of cartridges, requiring of a solution.”
I have never talked about eddy currents, I have always referred my concerns to any stray flux that could cause problems!!

Finally Arthur states that:
“Flux does, however, escape from rotor’s magnet. Unshielded it induces voltages in the sensitive generator of cartridges, requiring of a solution.”

My guess is that Arthur will need to shield the platter underneath by incorporating probably a Mu metal plate, which is very effective at shielding for flux. Technics use it to shield their transformer.
Alluminium and copper do have a shielding and flux defusing effect when they are interpose between a flux source and an interactive element such as another magnet or a coil. Albeit less than Mu-metal, which is the ultimate. In fact Mu metal does contain about 5% of copper ( although the copper may be added for ductility), the rest being nickel and Iron, having a relative permeability of about 100,000 compared to 2,000 for steel.

In conclusion, I have recently been active in pursuing the production of an Acrylic platter, mainly for my own interest.
And to my surprise; I found that a 25mm slab of Acrylic 330mm square only costs $54.20 !!! (In the UK it would be less.)
About 30 pounds in UK money!!! and how much is this platter going to cost??

So what are we talking about here, when we say:

“Why go all out to screw punters with a more expensive platter that could then itself be further improved?
Made no sense to us. We stuck with acrylic.
(Save the difference towards our arm and get yet more improvement!)”

And finally:

“1200’s have excellent overshoot characteristics. We retained this by optimising various of the platter’s dimensions to match the inertial load, motor power and servo. (Increase mass / inertia willy nilly and stability is adversely affected. It’ll work but not as designed.)”

“dimensions to match the inertial load,” I rather think there could be an appropriate response to that!! (Something about the exhaust end of a Bull) But I will not go there. Arthur should really know better, but then I know he does!!!

Finally a quote from the Time Step web site from the man himself:

“I have used several German turntables and realised that nothing beats a solid aluminium platter for ultimate sound quality and stability. But an Acoustic Solid Royal turntable costs nearly £8K without an arm and it still doesn't have the pitch stability of a direct drive.”

http://www.time-step.net/showthread....L-1210-Platter

So, who are we kidding???

[Mike_New]

Hi Ernest,

This thread has been a truly interesting read and am thankful to both Mike and Arthur for their contributions explaining the magnetic flux from the Techie motor.

Out of curiosity, I decided to do a simple test with my simple compass.

I took off the MN platter, and held the compass near the motor coil, and when I pressed on the start button, the needle moved and pointed straight at the direction of the coil. Did this a few times and the results were the same.

Then I placed the MN Platter on and did the same, and held the compass at the same position. The needle stayed put.
Now, of course this is a simple crude test at best with a not so sensitive compass...but the platter seems to provide some shielding. How much shielding, I can't say. Will leave it to the experts to do the testing.

Thank you for doing that test for me, I did not read your post before replying to Arthurs, as sometimes down under we seem to get out of sync with the UK.