Exact dimensions of the SL-1200MK platter anyone?

[opcode66]

The Numark tables are advertised as high torque with 4.5kg-cm

The Technics turntables are 1.5kg-cm

So, going by specs, Numark has a lot more torque than Technics.

I'm going to my studio tonight. I will try pulling a platter, flipping it, doubling up on platters on one turntable and will see how it turns.

[mossboss]

Hey Flo
I wil dig up a used motor fisher and pay keel for you in Australia and bring it along on a my next flight to London it may be a good try
I have no time to screw around either but I am happy to do this for you
It is no big deal as I only travel with hand luggage so I have up to 20 k to use up they go for very little money from junk yards or when people put out they hard rubbish once a year for council collection you can pick up the whole washing machine from the street
They don't like it at all but and than again phew!!!
It's only going to be melted down somewhere in China
Cheers

[opcode66]

Tests were not that promising. I'll edit and post some video tomorrow. With the added weight of another platter the motor was strong enough to start on its own. So, I was wrong about that. I was also able to maintain constant speed when freely rotating.

However, once I put the pad of my index finger on the top of the second platter simulating the mild downward force of a cutterhead the speed become entirely erratic. Just a slight amount of pressure caused drastic fluctuations. I tried the same test with just one platter. The speed was much more constant with downward pressure on the platter. In fact, it took quite a lot of pressure from my finger to cause the same amount of fluctuation.

Therefore, added weight to the platter on a standard SL1200MK2 with the addition of slight downward pressure is a recipe for disaster. Totally flutter city.

I will edit the couple of clips together with some captions and post to youtube tomorrow or over the weekend.

[tubefan]

I don't have schematics yet, but I've opened an SP02, seems to be very similar to SP10mk2, just everything is more expensive...

So in SP10mk2 there's a set of windings that generates 3 sinusoidal signals at the frequency and phase relationship needed by the drive coils. So there are three amplifiers that you can control the gain of, and these drive the drive coils of the motor.

The speed feedback is through a 'frequency generator', it's a set of windings and a toothed gear that create a high frequency sine wave that can be compared with the divided down crystal frequency to do phase locking (I think they converted freq->voltage and the control loop is in voltage domain in this one). But I have to read the SP10mk2 schematics again to remember exactly how this works. Anyway, sort of an expensive motor, the way they did it. Everything stays perfectly aligned, which is really nice... And mostly analog, and no switch-mode supplies or microprocessors, nice for the studio...

The VMS80's system is much simpler, but harder to align. Large DC brush motor, similar number of poles to a capstan motor. Optical tachometer on the motor. Flex coupling to the platter. And the parts are expensive, $1000 motor, $500 optical encoder, plus circuitry...

I like optical tacho plus brushless better than either of these other methods.... But it has to be zero or low cogging motor. I haven't found a cheap one I liked yet.

[opcode66]

Here is the video I took of my double platter test. Edited. With captions.

https://www.youtube.com/watch?v=QE95_g69jDg

[scalawag]

Here is the video I took of my double platter test. Edited. With captions.

https://www.youtube.com/watch?v=QE95_g69jDg

Hi!
Newbie here! Don't be rude. I've read a lot of posts the last month before registering.
Do you have the torque mod on your sl1200?

[opcode66]

Nope. Mine are not modified. They are perfectly calibrated.

The torque mod only adds about 0.5kg-cm. Maybe 0.8kg-cm. It really doesn't do much. The results would not be much different. How do I know? Because I had test discs cut on a number of systems that rely on a Technics 1200. That was over 3 years ago. When I was considering what sort of lathe to purchase. I finally decided to purchase a Neumann VMS70 because I was ultimately unsatisfied with the results from other turntable based lathes.

Every cut that came back to me from a system that relied on a Technics turntable without a motor replacement (so factory motor with or without torque mod) came back to me with flutter. I'm a dj. I play deep house. If there is flutter I hear it immediately. It means I'm constantly fighting to maintain a blend. I typically hold 2.5 to 3 minute blends. So, if a record is cut with flutter that becomes very challenging. I might as well play disco records then... Since they used real drummers who naturally have flutter...

[scalawag]

Thanks opcode66.

[opcode66]

If you don't add some sort of custom platter the flutter is minimal. I will say that.

[scalawag]

I don't want to steal the OP topic, so i'll make my questions on a new post.

[djlithium]

Tests were not that promising. I'll edit and post some video tomorrow. With the added weight of another platter the motor was strong enough to start on its own. So, I was wrong about that. I was also able to maintain constant speed when freely rotating.

However, once I put the pad of my index finger on the top of the second platter simulating the mild downward force of a cutterhead the speed become entirely erratic. Just a slight amount of pressure caused drastic fluctuations. I tried the same test with just one platter. The speed was much more constant with downward pressure on the platter. In fact, it took quite a lot of pressure from my finger to cause the same amount of fluctuation.

Therefore, added weight to the platter on a standard SL1200MK2 with the addition of slight downward pressure is a recipe for disaster. Totally flutter city.

I will edit the couple of clips together with some captions and post to youtube tomorrow or over the weekend.

Hey Opcode, as I mentioned in an earlier post reply I was considering having the SL1200 just be a "lathe" but not actually do the spinning at all. The platter extension im considering would have grooves cut into the side walls of it for a belt to drive it, driven by another motor of some kind. I would just need to figure out the right diameter of the groove, belt size and what kind of motor to use plus the smaller wheel mounted on that for the belt to attach to. Then figuring out the speed should be easy because the strobe dots of the original SL-1200MKII are there on its platter underneath the raised platform on top of it that im considering getting made.
If the motor driving the thing can be dialed in nicely (variable speed) then I think this can work.

[dubcutter89]

I was considering having the SL1200 just be a "lathe" but not actually do the spinning at all. The platter extension im considering would have grooves cut into the side walls of it for a belt to drive it, driven by another motor of some kind...

To me this sounds like using the Technics as turntable bearing only.
I don't have one, and the price for used ones is >=400€ !!
So if you don't use the Technics you don't have any limitations in size or whatever,
and I'm sure you will find a nice bearing for way under 400€ ...

just my thoughts...

[emidisc]

Surely the flutter on the YouTube clip is caused by the lack of friction between the two platters.............?

Emidisc

[opcode66]

Not at all...

The platter has a magnetic ring in the middle. That is how the direct drive motor works. The magnet is on the platter. The coils are fixed underneath the platter surrounding the bearing. The platters actually grip together very well. I think in part due to the magnetic rings on each. There was no slippage. And, I wasn't even pressing hard until i went back to a single platter.

Anyway... If the top platter were slipping (which it wasn't) then the dots on the bottom platter would not have displayed as much flutter. In fact they would appear more solid. The dots that i focus on in the video (and which are illuminated by the red side stobe) are on the bottom platter.

[mossboss]

The magnetic ring you refer to is not exactly such
It is magnetized in segments which are the poles of the motor
If you place a plastic film on the ring and pour some metal filings you will be able to see quite clearly where and how many poles the motor has
The coils on the base do not necessarily represent the pole count per se as it is the relationship/ratio of permanent to coil magnets
You most likely find that the coils are pulsed with AC so as to provide pole reversal N/S as well as the desired speed
It is called a permanent magnet direct drive DC but there is no such thing
All motors regardless are AC or else they will just sit there humming instead of spinning
Flutter is the end result of the gap between the segments on permanent magnetized areas on the ring as well as the flat wound coils on the base
So the more poles the less flutter as the gaps between the poles is smaller
The ferrite material used in making the ring is magnetized after it is formed in it shape diameter etc by induction
There is a physical limit to the areas magnetized
The ferrite particles have a certain amount of bleed so the non magnetized area has to have a certain amount of space between each pole
Technology has moved on there new and better materials available now as well as techniques so as to maximize pole count on a given say ring
But as in all things it is a case of how many units are to be made so as to make the development cost viable
So we are in essence stuck with what is easily available including 40-50 yo old machines
By the way weight on a plater which has a perm mag under it with any other magnetized or even magnetic weight on it will show up more flutter due to the field/flux been interfered with
Also none of these motors have any down load thrust bearings, any more weight past the designed load will add down force load on the ball bearings or phosphor bronze bearings normally used accentuating the issue
Cheers

[opcode66]

Ok, I'm just going to stop responding to this thread. If someone is going to use only the bearing and case from a technics tuntable, and replace all other parts then they may as well not start with a tecnics turntable to begin with. Like I've said since my first post, there are better motors and bearings to be had off the shelf these days. You would spend more effort and likely more money starting from a technics turntable then you would with a custom design.

If you can wait a couple years I'll have my lathe kits completed and ready to be sold.

[emidisc]

Another thing worth remembering with the SL1200 is the magnetic field around the centre of the platter during operation, as I recall this was the reason that vynalium did not recommend using their dub cutter for 7" discs due to the magnetic field interfering with the cutter head.

Emidisc

[vmspoland]

Hi Op,

I'm not disagreeing with your basic premise. That is, the 1200 will have problems once you add the drag of the cutter into the equation. It was not designed to deal with that kind of load. If you just want to add a heavier platter to the 1200 and use it for playback, you should be ok. Whatever torque the motor can produce will cause the mass to accelerate to its final speed. More mass added means more time to reach speed. If the 1200's bearings were frictionless this would be true for any amount of added mass, but in the real world, there is some friction due to the bearings and they will add some amount of extra drag as mass is applied. I'm sure if you went crazy, the 1200 would fail to start, but within reason, adding mass should be ok.

As far as a 1200 having no bearings, that's crazy talk. They may not be precision ball bearings, but there is some form of bearing that the platter rotates on.

Mark