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Item Audio "Spoke" for the Linn LP12 anybody..?

Darryl I'd pony up to cover costs..

Mtrei, where do you think the mass is concentrated in the Linn platter, at the centre? Based on their densities the Roksan platter would have to be nearly 3 x times as thick at the periphery to match the mass distibrution of the Linn.
 
oh and the roksan platter is pretty thick at the edge a good 2 cm's from memory, way way thicker than the linn which is basically just a curved bell like lip.....
 
I am not being critical of the Roksan in any way, as you say, the edge of the Roksan platter is thicker than the Linn, but then it is aluminium which is very much lighter than the Zamak the Linn is made from - it's six of one and half a dozen of the other.
 
pure sound said:
I can't see why it would be difficult to produce such a disc. It would just be one track with a constant tone and then elsewhere a heavily modulated track with some nice big LF excursions. The problem would come in installing 2 arms on some decks to allow them to play the two tracks simultanously!
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The idea of course was to cut a single track with both tones. I think Barry was skeptical whether the lathe could cut this without introducing some of the same problems that we are talking about testing for.
 
YNWOAN said:
I am not being critical of the Roksan in any way, as you say, the edge of the Roksan platter is thicker than the Linn, but then it is aluminium which is very much lighter than the Zamak the Linn is made from - it's six of one and half a dozen of the other.
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The rim of the Roksan platter is about 21mm thick, while the rim of the LP12 platter is about 6mm. I don't have a good scale for weighing these, but to the nearest 1/2-lb, the Roksan outer platter is 4-lb, while the LP12 outer platter is 5.5-lb.

With regard to friction, with a properly cleaned and lubricated Roksan bearing and platter, if you put a coin near the edge of the platter at the three o'clock position, then lift the rear of the turntable by about a 1/2 inch, the platter will rotate until the coin is near the 9 o'clock position, then swing back toward 3 etc, then continue to swing back and forth several times until the coin finally settles several minutes later at the 6 o'clock position.

If you want to see a really low torque and inertia turntable, check out the Origin Live models. I was once working on one, and when it came to tweaking the pitch, the owner said I needed to use the tiny record label sized strobe disc OL supplies. This is because the platter run noticeably slower when the cartridge is playing a record, and you need to set the speed while playing! Unbelievable.
 
darrylfunk said:
we are talking inertia though...not weight or thickness.
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Yes (I know), but the inertia is actually greater on the Linn as although there is less metal at the edge, the mass of that metal is significantly higher.

It's not a criticism of the Roksan (I think the platter is very nicely executed), the reduced inertia is offset by the reduced torque of the motor = as I said, it's six of one and half a dozen of the other.

I worked out the mass of all the individual sections of the LP12 platter a couple of years ago when I had some made from alternative materials. There is little value in comparing platters in this way.
 
well touraj measured the linn and said that the roksan was designed to have much higher rotational inertia and claims it in the press and brochures still i think....so again we will have a pfm-er vs a manufacturer....who knows the truth?

from a review which included a chat with touraj....

The platter itself is about half the weight of an LP12 platter, but because it has it's mass concentrated at its edge the total inertia that the record sees is actually higher whilst giving the bearing less mass to cope with. It's split into inner and outer platter and each is tuned to different frequencies.

who wants to input the figures? Lol....

http://www.livephysics.com/tables-of-physical-data/mechanical/moment-of-inertia.html
 
darrylfunk said:
i though linn used british mazak not the higher quality american zamak!!!

probably bugger all in it really though.
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Yes, they did - the name was only a licensing issue though,

In recent years the weight of the Linn platter has slightly reduced but the dimensions are the same. It seems likely that they have chosen a Zamak option with slightly less zinc for stability and machining reasons (there are a number of subtly different Zamak alloy options).

_________________________

I would have to measure the Roksan. Zinc is over twice the density of aluminium but it's possible the outer ring of the Roksan platter weighs more than that of the Linn - offset against that will be the mass of the top etc. (which still impact upon the overall inertia); irrespective, the speed of rotation is the same. I know how the Roksan platter is constructed.

I'm sure the Roksan platter has a greater inertia relative to the torque of the motor, but in an absolute sense.......perhaps. I could work it out but frankly, it's not worth the time. As I said earlier, comparing individual components in this manner is quite pointless.

Anyway, I sense this quickly spiralling into pointless argument of an irrelevant issue - so I will leave it there.
 
YNWOAN said:
Yes (I know), but the inertia is actually greater on the Linn as although there is less metal at the edge, the mass of that metal is significantly higher.
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I don't believe that for a minute. While the density is higher, I doubt the mass would be higher with about 1/4 the volume of material.
 
sq225917 said:
Mtrei, where do you think the mass is concentrated in the Linn platter, at the centre? Based on their densities the Roksan platter would have to be nearly 3 x times as thick at the periphery to match the mass distibrution of the Linn.
Click to expand...

Linn (left) and Roksan (right) outer platters.
roksanlinn.jpg
 
YNWOAN said:
. I could work it out but frankly, it's not worth the time. As I said earlier, comparing individual components in this manner is quite pointless.

Anyway, I sense this quickly spiralling into pointless argument of an irrelevant issue - so I will leave it there.
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it's not a deal breaker at all is it really, when push comes to shove?

i think we can both agree they both have nice platters....i dont think an argument would get the thread anywhere either.....:p
 
Looking at the platters the roksan does indeed appear to be thick enough to have greater rotational inertia
 
MTrei said:
The idea of course was to cut a single track with both tones. I think Barry was skeptical whether the lathe could cut this without introducing some of the same problems that we are talking about testing for.
Click to expand...

That wouldn't matter. Wow is superpositive. All we need to know is the original frequencies, and we can measure the difference between the two decks, even if they both wow. If one deck produces less wow than the other then the difference is at least that much. Thorough measurement of wow requires building up a profile with various inputs. One deck might have a narrower band of sensitivity to input frequencies than another. Two frequencies aren't really enough to investigate a deck's general susceptibility to signal induced speed oscillation.
 
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