What to do with a TT2?

[shane]

May I add that the belt must NOT rub on the pulley shoulders, but as centrally as possible.

See my last-but-one post!

[DSJR]

See my last-but-one post!

I did, but that was relevent to original ones. I thought you'd posted that the later model lost the adjustment? My bad if I'm wrong, apologies...

[surayne]

Right, I've hit a bit of a snag. I removed the subplatter to check the bearing and change the oil, but it seems that the bearing is stuck in the well. I've tried dislodging it with the end of a cotton bud but it's not budging.

Is this a common problem? How serious is it and what can I do to rectify it?

[pure sound]

Not really serious as the ball isn't intended to turn. Provided there isn't a flat worn on it it should be fine as is. Just clean the bearing well out as much as you can, add some new lubricant & re-fit the spindle. Do keep the surface of that inner hub clean & free from oil/grease/fingerprints.

If you do want to take the ball out & clean & reposition it, I'd fit a transit bolt to lock the subchassis in place, remove the arm & turn the whole deck over. Tapping the bearing housing (or the whole deck) from underneath should cause it to fall out.

[AlfaGTV]

Okey, now let me show you the differences between the earlier TT2 and its double speed pulley and the later TPS external motor control version with its single "straight" pulley.



Here is the later pulley, which i belive is quite similar to the one on Linn LP12's


The belt though has a tendency to wander on the pulley, making it difficult to adjust susp. to 100%. Correct me if im wrong but the rubber belt will always strive to the "highest" part of the pulley if it is convex in shape like the pulle on the images further down belonging to the early TT2.



This is an extreme picture, but it shows that the belt will almost always be on the verge of the pulley, top or bottom.


Below is the pulley from the early TT2:

This has convex belt surfaces and flanges to prevent wandering. It's quite easy to adjust this one to perfect running.



This last pic shows the belt in a running state, perfectly centered on the pulley.


I can appreciate the desire "not" to use a convex pulley as imperfections in the drivebelt will always create speed variations to a bigger degree that with a straight pulley... At least imo and theories!

So, what is the best way to make the belt stay on the flat portion of the pulley on the later version of the TT2?

/Mike

[YNWaN]

This is an extreme picture, but it shows that the belt will almost always be on the verge of the pulley, top or bottom.

Why do you say that this is an extreme picture? The belt is riding in, essentially, the correct position.

Below is the pulley from the early TT2:

This has convex belt surfaces and flanges to prevent wandering. It's quite easy to adjust this one to perfect running.

To be honest, I don't see how one is easier to adjust than the other? A strobe is required for the first, but at least it directly adjusts the speed (by adjusting the effective diameter that the belt sees).

I can appreciate the desire "not" to use a convex pulley as imperfections in the drivebelt will always create speed variations to a bigger degree that with a straight pulley... At least imo and theories!

No, there is no inherent disadvantage to a crowned drive pulley.

So, what is the best way to make the belt stay on the flat portion of the pulley on the later version of the TT2?

Both the drive pulleys you show are effectively the same thing, crowned pulleys. The only difference is that the first allows the profile of the crown to be altered by tilting the vertical axis of the motor relative to the plane of the belt. The second assumes that this mechanical adjustment will be made electrically. Neither pulley solution is better, or worse, than the other in mechanical terms as both achieve belt centring my the same method, and a crowned pulley is the best solution.

However, if everything is accurately machined to a sufficiently high tolerance and the belt produced similarly, belt wander should not be an issue even on a straight sided pulley (unfortunately this is not always true, even for many 'quality' turntables).

[shane]

Interesting. It's pretty much the same as the Linn pulley, and I've never understood the logic behind it. It's not possible to get a flat belt to run centrally on a pulley without a crown. It just won't do it. When I was trying to work out the design of the original pulley, I had to pretty much guess the radius of the crown. All the information I could find (there was no internet in those days, remember) came from research done in Victorian times when factory and farm equipment was driven by flat belts, and it was all pretty vague. You don't need much of a crown and in theory the pulley edges aren't needed, but you have to have something. On the Linn-type pulley, the belt just treats the angle between the flat portion of the pulley and the conical part as a crown and runs on that, as shown perfectly in your second picture. (Brilliant photos, by the way!)
What I could never work out was which diameter to use to calculate the speed. In the end, I think we just tried reducing the diameter by degrees until we got it right.

As far as removing the ball from the bearing is concerned, I wouldn't bother. The ball is aclose fit in the bearing. If you take a new bearing with no oil in, the ball takes about 20 seconds to reach the bottom of the bearing. Introduce some oil, and the oil seals the minute gap around the ball almost perfectly. If you try to force the ball in under these circumstances, the air pressure will force the brass plug out of the bottom of the bearing.Iin the same way, it's almost impossible to remove the ball once there is oil in the beaing because air cannot get past the ball. The only way I've ever managed it is to push the ball and the plug out of the bottom together. Not recommended!

There shouldn't really be any need anyway. Cotton buds or a rolled-up soft clotth will be sufficient.

[YNWaN]

The diameter of the vertical element of the pulley defines the maximum diameter available and should be a few percent greater than the ideal. The angle of the conical element effectively defines the sensitivity of asjustment.

[DSJR]

Having the Linn style pulley (probably where the idea came from?) enables easy fine running speed adjustment. Use a non-mains high frequency strobe (avaiable on ebay I think) like the 300Hz Linn one..

At the time, the TT2 sounded slightly different to the Lp12, and of course, anything that sounded different to the LP12 was automatically worse I reckon that these days, the TT2 with modern takes on mat and tonearm, may well be a lot better if truth be told, especially the later model with the outboard motor supply, which I don't remember for some reason (probably because their speakers were being changed at around the same time and we weren't as keen on the new models (probably wrongly, but big Linn/Naim dealers were very narrow minded back then).

[YNWaN]

Well, it won't be 'a lot' better because in real terms it isn't all that different - but, by the same token, it won't sound all that worse either. However, besides just the superficial design, a lot depends on the concentricity of components, accuracy of machining and tolerances achieved.