New acrylic platter for the SL-1200/1210

[Marco]

Indeed, Martin.

Incidentally, you've been rather quiet on a thread which I thought would have been of significant interest to you....

I'd therefore be interested to know what your thoughts are on what's been discussed so far regarding the acrylic platter

Marco.

[MartinT]

I've read this thread with interest (and personal interest since I use Mike's bearing, platter and base plate) but no-one yet seems to have considered the effect of any stray magnetic fields on the type of cartridge used.

Due to the number of windings and size of the coils used, I would expect that there is a spectrum of sensitivity to magnetic flux ranging from moving iron (the worst), moving magnet, moving coil down to types that would be impervious such as strain gauge, piezo and optical.

The only practical observation I can make is that a Grado Prestige Gold (moving iron) is known to be very sensitive to magnetic and electromagnetic fields and indeed sounds horrible in my Technics. Some might say that it sounds horrible anyway. On the other hand, low output moving coils are hardly susceptible at all and that is proven by all my MCs sounding very good in the Technics.

This is not a very scientic observation but someone should be able to measure the effect by connecting the cartridge outputs to an oscilloscope and running them over the spinning platter. In fact, I may try this out myself when I have the time.

[Marco]

Good point! You see, that's why I wanted your input

Perhaps either Arthur or Mike (or anyone else) would care to comment on that point?

Marco.

[MartinT]

Incidentally, you've been rather quiet on a thread which I thought would have been of significant interest to you....

Indeed, I had missed this thread until last night.

Contrary to some opinions, I find the look of the acrylic platter quite nice. However, like you Marco, I'm only concerned with sound quality and am keen to discover the fruits of Arthur's design once someone gets their hands on one. Something tells me that, however it sounds, it's going to be different from the stock and MN platters.

It's really going to have to go some to beat an MN platter with Achromat combination since I can't help feeling that we have the best of shielding, rotating inertia and record coupling going on there.

[colinB]

Before i owned my 1210 , i read many online discussions referring to distortion from the cartridge when tracking the inner grooves of the lp and how the cause was thought to be the transformer underneath the platter.
Is it possible this problem is actually the stray flux and nothing to do with the power supply?

[Spectral Morn]

I've read this thread with interest (and personal interest since I use Mike's bearing, platter and base plate) but no-one yet seems to have considered the effect of any stray magnetic fields on the type of cartridge used.

Due to the number of windings and size of the coils used, I would expect that there is a spectrum of sensitivity to magnetic flux ranging from moving iron (the worst), moving magnet, moving coil down to types that would be impervious such as strain gauge, piezo and optical.

The only practical observation I can make is that a Grado Prestige Gold (moving iron) is known to be very sensitive to magnetic and electromagnetic fields and indeed sounds horrible in my Technics. Some might say that it sounds horrible anyway. On the other hand, low output moving coils are hardly susceptible at all and that is proven by all my MCs sounding very good in the Technics.

This is not a very scientic observation but someone should be able to measure the effect by connecting the cartridge outputs to an oscilloscope and running them over the spinning platter. In fact, I may try this out myself when I have the time.

Yes indeed Martin

I once had major problems with a Grado on an Avid Diva mk1 TT. This was due to the suggested placement of the motor at the front of the turntable (under the arc of the cart). The motor was not shielded thus created major hum problems. The solution was to use the motor in another position under the deck away from the cart. Thankfully this was possible but the question I asked of Conrad via email at the time was why not shield it from the off ? No satisfactory answer was given bar I suppose it would cost too much. The Diva sold for £1200 at the time.

The new version of this deck is quite different and everything is fixed in position. The idea of the original was you could use two arms and positioning the motor at the front (it had a logo on it) allowed this.

Regards D S D L

[Marco]

A lot of people from all over the world (which is good for AoS) do look to this forum for guidance and advice.

Ain't that the truth....!

Hi Martin,

It's really going to have to go some to beat an MN platter with Achromat combination since I can't help feeling that we have the best of shielding, rotating inertia and record coupling going on there.

I'm inclined to agree, but I'm also aware that Arthur is not your run-of-the-mill designer. In my experience, he always thinks laterally and looks at the bigger picture, so the acrylic platter he's designed will no doubt contain some valuable sonic qualities.

Marco.

[Mike_New]

Hi Marco, Martin,

Marco has asked me to give my thoughts on Martins observations concerning the interaction of various types of cartridges in a stray flux.

I believe Martin is correct when he talks about the other affects of stray magnetic fields on various makes and types of cartridges.

However it is now my thought that any stray flux fields could more adversely affect MC cartridges by their interaction with the powerful magnet which these newer quality MCs use. Rather than the interaction with the coils, which was my first observation earlier in this thread.
I have a Benz Ruby MC and the power of the magnet is frightening. (they use rare earth magnets I believe) do not ever go near it with a metal object.

Theoretically, what could happen I believe, is that at a point, the magnet of the MC can be attracted downwards by the stray flux field, which will in turn cause the stylus to move forward along the track as it is compressed against the record.
Now as the flux is alternating at the rate determined by the number of magnetic poles on the rotor magnet, the MC could oscillate in the vertical mode, causing the stylus to move backwards and forwards in the groove.
This will of course have a modulating affect on the reproduce sound.

I have however placed my cartridge over a CD (recording side up) and ran my platter at 45rpm. Even at high volume (effectively 180W per channel) I could not discern any modulation that could be attributed to the stylus moving vertically in sync with the rotation. I did however have trouble getting my arm to stay steady in the one spot.
This is not the ultimate test, I know, as it would be nice to have, say a 1Kz tone recorded at this point from which to replay.
Interestingly it happens that the edge of a CD just about coincides with the point at which any stray flux from the rotor magnet would be greatest.

I did not try this using the OEM platter as I did not want to disturb my setup. I will leave Martin or others to give it a go.

[MartinT]

Good lateral thinking there, Mike, I hadn't considered the effects on the magnet itself. I will at some point fire up my 'scope and test various cartridges for output when held over the rotating platter to see if there is any real effect.

[DSJR]

Hi DSJR,


I do not think you are really in tune with what historically has been happening.....

When I designed my High Precision Bearing I did so with the continuing use of the OEM platter in mind. People then asked me to design a new heavier high quality platter, as a component of the phased upgrade path; which I then proceeded with.

My bearing does not have drag!

Rather it is a high precision honed fit to the outer bearing which is why any mechanically un-informed persons would maybe think of it as drag. The rotation is as smooth as silk, but firm with absolutely no looseness. Which is what is required of a high quality bearing in the context of an audio application. (Think also the bearings in high quality Tape Decks)

The Stock Bearing of the SL1200 has no 'drag' as DSJR refers to it, simply because it is a low cost component built to a price

Unfortunately high precision engineering is labour intensive and involves high precision machine tools and setup times.
For instance the shafts for my bearings are machined on a $200,000 Swiss NC lathe before finish grinding and Gas Nitriding.

The bearing housings (which I machine) are then precision honed to fit the shafts.
It is this overall process that does cost money, and that all other wouldbe vendors of bearings have studiously avoided.
Rather they have all resorted to re-engineering a new shaft and load device into a very weak die cast housing.

Set up times and machine time must be computed into the pricing equations as fixed costs to be amortised over the size of the production run.
That is why I produce my bearings in batch's of 25. I could indeed 'forward- order' 100 shafts but the up-front money would be to high for my liking.

The bearing was never ever designed 'specifically' for heavier platters as DSJR suggests!!

The bearing will work just as well on an acrylic platter as any other
(Assuming that is, that the platter has been machined correctly so as to position the vital components into their correct running location axially)

DSJR suggests that using the stock platter (with my bearing) could improve things!! Does he not know that at this point in time there are over 80 happy users of my bearings around the the world. Not including forward orders from Spain, Portugal, Lithuania, and of course many in the US and Asia.

Bloody 'ell Mike, anyone would think I was having a go at you or summat and that my "claim" that your bearing has "drag" is a negative thing. I don't believe I suggested that in the slightest.

This debate is on the verge of getting personal. My techie won't be able to benefit from any of this in any case, so this "uninformed amateur" will bow out at this point