Oxford Crystal Reference restoration

[Spectral Morn]

When I say "play" I don't mean to imply it is loose and rattling about. It has one natural resting position (probably the wrong one), and the platter weight tends to keep it in that position. However it is not rigid like a tonarm bearing and can move.

I will probably have to take it apart eventually, but I am a little nervous as this is a critical component that up to now I have been careful not to disturb or even invert. I remember the first time Jon assembled it he did it in such a way as to suggest "don't mess with this" and there was an audible sigh from both of them that indicated a critical assembly milestone has been reached and it was plain sailing from there.

Or they could just have been messing with my head I wouldn't put it past them.

Ahhhh ! Okay yes if it was not perpendicular it would rise up and down as it turned. The bearing housing needs to be level and would appear not to be. Perhaps the three bolts holding it in place allow it to be adjusted/re-leveled.

I once had awful problems setting up a Roksan TT as there are three set screws underneath the bearing, which you can adjust to level the bearing. It took me hours to get this just right. At one point I nearly launched the TT out the open door of the shop I worked in at the time. You thought you had it right but looking at the side profile of the platter you could see it rising and falling. This rise was on the side where the bearing housing was off I got it done eventually but at that point I swore I would not do a Roksan again. Even my mana spirit level was of little help to me.

Regards D S D L

[peter]

Oops, Steve covered this a few messages ago:

Steve >> I discovered during routine maintenance and refurbishment of the oil (I used a good oil of the correct consistancy obtained from Audio Origami) that the bearing housing can be pivotted slightly but when the mass of the platter is applied, the bearing is centered and sits straight without any lateral movement.

I think that agrees with my "play" comment.

[peter]

Ahhhh ! Okay yes if it was not perpendicular it would rise up and down as it turned. The bearing housing needs to be level and would appear not to be. Perhaps the three bolts holding it in place allow it to be adjusted/re-leveled.

I once had awful problems setting up a Roksan TT as there are three set screws underneath the bearing, which you can adjust to level the bearing. It took me hours to get this just right. At one point I nearly launched the TT out the open door of the shop I worked in at the time. You thought you had it right but looking at the side profile of the platter you could see it rising and falling. This rise was on the side where the bearing housing was off I got it done eventually but at that point I swore I would not do a Roksan again. Even my mana spirit level was of little help to me.

Regards D S D L

That's exactly it, but in my case when it *is* level it does not turn about the centre, which causes the arm to swing in and out. It is as if the other end of the shaft from the one you can adjust is not correctly set (as if there were three screws at both ends, and the 3 that you cannot get at are set wrong). Possibly the large fixing beneath the subchassis is mis-positioned.

I am hoping that in reality the bearing is off because the sorbothane supports are not supporting the sub-chassis level, because fixing the supports would resolve that.

But I have Steves notes now so I will stop guessing and see what he has to say.

peter

[Spectral Morn]

That's exactly it, but in my case when it *is* level it does not turn about the centre, which causes the arm to swing in and out. It is as if the other end of the shaft from the one you can adjust is not correctly set (as if there were three screws at both ends, and the 3 that you cannot get at are set wrong). Possibly the large fixing beneath the subchassis is mis-positioned.

I am hoping that in reality the bearing is off because the sorbothane supports are not supporting the sub-chassis level, because fixing the supports would resolve that.

But I have Steves notes now so I will stop guessing and see what he has to say.

peter

you have my best wishes....

Regards D S D L

[John]

Try getting everything level (the base support chassis and platter) You probarly doing this but worth checking If not then a question of eliminating the cause
Best of luck

[peter]

I just looked under the bronze platter, the platter does not rest directly on the bearing housing, there are in fact 3 allen bolts near the hole that rest on the housing. One of these engages with the pin or butts up to it.

Now, the tiny gap between the bronze platter and the bearing (as viewed from above means that the point of contact is just the three allen bolts. It also suggests that the bolts need to be very accurately machined or be adjustable if the platter is to rest concentric to the bearing shaft.

It's starting to make sense.

I need to take a picture to show this but the camera battery is flat cos I forgot to unplug the usb cable, again

[peter]

More information:

I have located the original installation instructions. One point made is that not all the sorb mounts are the same. One has to bear a greater weight due to the tonearm, and is of differnt type. Its setting depends on the type of arm used as well and it is necessary to remove the platters adjust, replace platters, measure, repeat intil the arm weight bias is correctly nulled out.

Steves includes a tip that simplified this, as you can adjust the spike pentration without having to remove the sub-chassis, which I did not realise.

I can scan the instructions for future reference if that is helpful. It is an interesting read from the design perspective, and interesting to compare with Steves instructions/tips. There is also a detailed instruction on how to replace the bearing oil, with more description of the materials used.

The bottom line as everone has said is level, level, level (three times for stability!)

that means:

1) Top base plate must be level (4 feet/spikes at the bottom)

2) sub-chasses must be level (sorb bolts/chassis spikes) according to arm weight

3a) bronze platter is level (and concentric to bearing) by 3 hidden bottom platter bolt heads and upper 3 grub screws (very tricky, 6 degress of freedom, not including angle of platter wrt bearing.

4) Upper acrylic platter has to be level (concentric) so there is no gaps to the bottom platter. Note that if 3 is wrong, this is impossible. The only way to adjust this is to turn the platter through various angles and use the cig-paper test to find the best angle with optimum gap, OR, if its not level then repeat 3 until it is.

Perform wobble checks

Install arm/cart.

I had a problem with the sorbothane deforming in a no time. It occurs that I tend to have the turntable powered up 24/7 so the heat from the power-supply board could have accelerated the deformation, so the moral is "turn it off when not in use".

Sincere thanks to everyone for contributing so far.
Peter.

[Spectral Morn]

More information:

I have located the original installation instructions. One point made is that not all the sorb mounts are the same. One has to bear a greater weight due to the tonearm, and is of differnt type. Its setting depends on the type of arm used as well and it is necessary to remove the platters adjust, replace platters, measure, repeat intil the arm weight bias is correctly nulled out.

Steves includes a tip that simplified this, as you can adjust the spike pentration without having to remove the sub-chassis, which I did not realise.

I can scan the instructions for future reference if that is helpful. It is an interesting read from the design perspective, and interesting to compare with Steves instructions/tips. There is also a detailed instruction on how to replace the bearing oil, with more description of the materials used.

The bottom line as everone has said is level, level, level (three times for stability!)

that means:

1) Top base plate must be level (4 feet/spikes at the bottom)

2) sub-chasses must be level (sorb bolts/chassis spikes) according to arm weight

3a) bronze platter is level (and concentric to bearing) by 3 hidden bottom platter bolt heads and upper 3 grub screws (very tricky, 6 degress of freedom, not including angle of platter wrt bearing.

4) Upper acrylic platter has to be level (concentric) so there is no gaps to the bottom platter. Note that if 3 is wrong, this is impossible. The only way to adjust this is to turn the platter through various angles and use the cig-paper test to find the best angle with optimum gap, OR, if its not level then repeat 3 until it is.

Perform wobble checks

Install arm/cart.

I had a problem with the sorbothane deforming in a no time. It occurs that I tend to have the turntable powered up 24/7 so the heat from the power-supply board could have accelerated the deformation, so the moral is "turn it off when not in use".

Sincere thanks to everyone for contributing so far.
Peter.

No problem Peter, it has been fun and a real blast from the past......I did mention the different types of sorbothane early on....I just could not remember how many there were....old age creeping in.

I look forward to reading your post were you say its working and amazing.


Regards D S D L

[DSJR]

Gawd, it reminds me of the far more humble Manticore Mantra turntable. The glass top platter sat on three little adjustable studs and one was severely warned not to touch these when setting up...

[Snoopdog]

Hmmmmm! Interesting read!

It's quite obvious comparing the photos of the Oxford I owned and the one Peter has (seperated by just seven on the serial numbers!) that there are slight but significant design changes.

First the bearing housing. There was no 'pin' on the lip of my bearing housing and the bottom of the phosphur bronze platter sat flush on the lip of the bearing housing. No Allen bolt heads for contact with the model I owned!

Secondly, comparing the two photos of the underneath of the sub-chassis showing the base of the bearing housing. There are differences in the design and fitting of this component.

I am quite alarmed at the pictures showing the paper wedged between the two part platter. Mine was almost a gas-tight seal!

I do recommend Peter, that you carefully disassemble the bearing to examine the tiny ball bearing and thrust pad interface as I described in an earlier post.

You are correct that the thrust pad (which can be turned over when worn on one side) is held in place by three grub screws and can be adjusted.

Glad the notes I emailed you helped. I look forward to following this restoration project further.