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LP12 Bolt Mod

J

JMP

Member
Hi

I have a 1988 LP12 - corner braced plinth.

I've read about the cheap and effective Motor Corner Bolt Mod.

My questions

- Is it worthwhile if the top plate is correctly set?
- How can I test if the top plate is correctly set, e.g. no rattling?

Thank you!!
 
No, it's not worth doing if the problem doesn't exist.

You can test by removing the outer platter - then, with your index finger, strike the top plate in the corner where the motor is mounted. If it sounds like a dull thud then you are fine.
 
You can only really tell how well the top plate is fitted during assembly of the deck. So to check it properly you'd need to strip the deck down (i.e., remove the sub chassis) and then basically tap around the top plate edges to determine if it is solid with the plinth in all areas, particularly the corners. Then of course you're left with the job of re setting the deck which if not done properly could you leave you in a worse place overall.

The corner bolt does help in terms of ensuring that the motor corner area is well connected to the plinth so that motor vibrations are better damped, but if you have a well fitted top plate then it doesn't make much difference. What it did do was add more consistency to deck set up. You can do a mod by either drilling a hole in the corner area and the corner brace and fitting a long M5 bolt, or by picking up a S/H top plate with the corner bolt already brazed on, there are quite a few of these about now.
 
If you use a T-nut:

t-nuts-stainless-steel.jpg


You can tap the spikes flat with a small hammer and epoxy it to the underside of the top plate. You then drill a hole in the corner brace (you do need a corner braced plinth) and fit the correct length bolt - don't over tighten it. You are probably best drilling the hole first and using this to help align the T-nut for gluing.

Personally, I don't think you need to strip the deck to check for this issue and my suggestion paraphrased the Linn service manual.
 
You're probably right Mark, maybe a strip down is perhaps a bit of overkill but I find it hard to check the top plate connection when there are bits of hanging off it:)
 
I did it and think it's worth doing - a small difference but cheap and easy to do and these things all add up. Apart from stopping any rattles, maybe it does help transfer some motor vibration deeper into the plinth via the bolt / corner brace, as Roger suggested.

As Mark said above, just drill a suitable hole through the corner brace and araldite a T nut to the underside of the top plate is the easiest way. You can use the same bolt via a temporary nut on top of the corner brace to exert a little pressure on the T nut whilst the epoxy is drying.

FWIW: When Peter Swain was setting up my LP12, I noticed that he placed a lot more emphasis on the top plate fit than the fabled "bounce"...
 
Yes, I do think the top plate tightness to the plinth makes a significant difference and vibration at the motor corner is certainly not a good thing. Linn's solution of bowing the top plate is elegant in a sense but it isn't as effective as it could be. I've recently had a chance to play around with a Khan top plate and that certainly seems to give a more solid and consistent contact to the plinth (it bolts to it at a number of points).
 
I found it made a small but worthwhile improvement in tightening up the sound. However my bolt mod came apart as I hadn't cleaned the parts properly before epoxying. Haven't put it back yet as I'll wait until the spirit comes over me and I take it apart and swap the springs around etc. Cheers, Rolf
 
YNWOAN said:
Yes, I do think the top plate tightness to the plinth makes a significant difference and vibration at the motor corner is certainly not a good thing. Linn's solution of bowing the top plate is elegant in a sense but it isn't as effective as it could be. I've recently had a chance to play around with a Khan top plate and that certainly seems to give a more solid and consistent contact to the plinth (it bolts to it at a number of points).
Click to expand...

I think I am going to (well you are!) finally going to fit the Khan to my deck!
 
TPA said:

You can only really tell how well the top plate is fitted during assembly of the deck. So to check it properly you'd need to strip the deck down (i.e., remove the sub chassis) and then basically tap around the top plate edges to determine if it is solid with the plinth in all areas, particularly the corners. Then of course you're left with the job of re setting the deck which if not done properly could you leave you in a worse place overall.

The corner bolt does help in terms of ensuring that the motor corner area is well connected to the plinth so that motor vibrations are better damped, but if you have a well fitted top plate then it doesn't make much difference. What it did do was add more consistency to deck set up. You can do a mod by either drilling a hole in the corner area and the corner brace and fitting a long M5 bolt, or by picking up a S/H top plate with the corner bolt already brazed on, there are quite a few of these about now.
Click to expand...

You definitely want to check for rattles when it's stripped down. Too tight kills the sound!
 
John said:
You definitely want to check for rattles when it's stripped down. Too tight kills the sound!
Click to expand...

You are absolutely right, too tight kills the sound of both Khan and Karmen.

For those curious, they are both on dem at Cymbiosis. :)
 
John said:
You definitely want to check for rattles when it's stripped down. Too tight kills the sound!
Click to expand...
My LP12 has a well-fitted top-plate, to which I applied the bolt-mod as described. I certainly found that anything thing more than just nipped up to provide a light tension absolutely killed the Linn groove.

I have since fitted the Khan, taking care to secure the bolts with just enough tension for a secure fit.
 
Been there done (and undone) the bolt mod.

I found that taking time to get the top plate formed correctly is all that's required to make the motor corner (and switch corner) rattle free. The flaw inherent in the bolt mod is that it introduces one extra tuneable component into the (arguably) already too tweaky LP12. Aftermarket top plates with multiple 'bolts' are an extension of that - for good or bad.

Mr Tibbs
 
Mr Tibbs said:
Been there done (and undone) the bolt mod.

I found that taking time to get the top plate formed correctly is all that's required to make the motor corner (and switch corner) rattle free. The flaw inherent in the bolt mod is that it introduces one extra tuneable component into the (arguably) already too tweaky LP12. Aftermarket top plates with multiple 'bolts' are an extension of that - for good or bad.

Mr Tibbs
Click to expand...

I agree that it's the fit of the top plate that is the important issue, as opposed to the bolt per se, but as I said before, it did permit a greater level of consistency to be achieved and having now come across an awful lot of different LP12s I can tell you that the variability in set up is underwhelming.

The thinking behind things like the Khan is not really to enable a better connection to the plinth, but to actually act as a better platform for the motor and suspension as opposed to a a sheet of thin stainless steel where in order to work ok becomes exceedingly critical. The whole deck becomes a lot more predictable; the spring carrier bolts are now vertical so the suspension is easier to set up, motor vibration is absorbed and it's connection to the plinth is now much more effectively achieved.
 
Hi!
thanks for advices guys.
Will take time to check everything. Not sure I have the right dull thud when taping on the corner.
Maybe a full rebuilt would be a good thing.

Will see what I'll do. Unfortunately, I don't have access to LP12 expert/dealer around here, so will have to do this by myself.

Happy christmas everyone!
 
Thank you Gaius.
Yes, I know this thread. I made me a PDF of it. I also have a copy of the Linn Setup manual.
In fact, my LP12 is not that bad ;) I have managed to set it up quite nicely already (got it for more than 10 years), sounds quite good.
It has a very nice pistonic bounce, but I think I've overlooked a few details ....

JMP
 
^^^Excellent, sounds like you have it under control, if doing a rebuild I'd defiantly change the oil, springs and grommets, give me a shout if you need any parts.
 
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