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LP12 platter speed
2018-03-06, 18:02
Post: #1
LP12 platter speed
Hi,
I'm looking for some advice regarding my LP12, where I have difficulty setting an accurate platter speed.
The TT is of approx 51000 vintage, pre-Cirkus, no mods, but a recent service (Valhalla refurbished) and new belt. The platter has what seems to be a good bounce, and runs true and level, and using a test LP I get reasonable results for tracking etc.
However -
Having read much of the advice and warnings on this forum I have tried adjusting the motor speed screws (carefully), and can get to about 99.6 revs per 3 minutes, but cannot get it faster. At this stage any further up-speed adjustment causes the belt to foul the top of the belt guide.
While looking carefully at this I realised I could also hear both a hum (apparently from the motor) and a 'th-th-th' sound (perhaps to do with the belt?).
During further experiment I gripped the top of the platter spindle between thumb and forefinger in order to slow down the rotation and hear if any of the noises changed. While doing this I found that I could move the whole platter/armboard (and presumably sub-chassis) assembly in relation to the motor, without exerting much force. The top plate stayed still in the plinth. I repeated this with the deck switched off and with the outer platter removed.
It seemed to me that if the platter moves relative to the motor, then I can never get a truly stable speed.
Reading Peter Swain's LP12 Setup guide, p3/33 he states:
“Once the springs, grommets, washers and nuts are fitted then the sub-chassis can no longer move about freely. “
I assume from this that the sub-chassis should not move at all, in which case I have a problem to resolve, but could anyone confirm this for me before I do anything else?
Motor and other noises can be dealt with next!
Many thanks,
Nick
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2018-03-06, 18:31
Post: #2
RE: LP12 platter speed
(2018-03-06 18:02)nickhews Wrote:  Hi,
I'm looking for some advice regarding my LP12, where I have difficulty setting an accurate platter speed.
The TT is of approx 51000 vintage, pre-Cirkus, no mods, but a recent service (Valhalla refurbished) and new belt. The platter has what seems to be a good bounce, and runs true and level, and using a test LP I get reasonable results for tracking etc.
However -
Having read much of the advice and warnings on this forum I have tried adjusting the motor speed screws (carefully), and can get to about 99.6 revs per 3 minutes, but cannot get it faster. At this stage any further up-speed adjustment causes the belt to foul the top of the belt guide.
While looking carefully at this I realised I could also hear both a hum (apparently from the motor) and a 'th-th-th' sound (perhaps to do with the belt?).
During further experiment I gripped the top of the platter spindle between thumb and forefinger in order to slow down the rotation and hear if any of the noises changed. While doing this I found that I could move the whole platter/armboard (and presumably sub-chassis) assembly in relation to the motor, without exerting much force. The top plate stayed still in the plinth. I repeated this with the deck switched off and with the outer platter removed.
It seemed to me that if the platter moves relative to the motor, then I can never get a truly stable speed.
Reading Peter Swain's LP12 Setup guide, p3/33 he states:
“Once the springs, grommets, washers and nuts are fitted then the sub-chassis can no longer move about freely. “
I assume from this that the sub-chassis should not move at all, in which case I have a problem to resolve, but could anyone confirm this for me before I do anything else?
Motor and other noises can be dealt with next!
Many thanks,
Nick

The motor position is fixed. The sub-chassis floats on springs. It can move relative to the motor.
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2018-03-06, 18:42
Post: #3
RE: LP12 platter speed
Hi Nick,

Firstly, you’re misinterpreting Peter’s meaning or reading it out of context. At that point in the guide, he’s talking about fitting the subchassis. Once the subchassis is positioned over the suspension bolts, you have to very careful not to knock it against the bolts, as you could knock them out of true, or damage the subchassis (more important if it’s a high value Keel). All he’s saying is that, once the grommets and springs are fitted, the subchassis is no longer free to drop or bang against the bolts. What he’s NOT saying is that it is locked in place and unable to move!

Secondly, the LP12 is a suspended subchassis turntable, so it has to be able to move in order to filter out external vibration. The main bearing/platter and arm/cartridge are rigidly fixed to the subchassis and do not move in relation to each other. The motor is rigidly mounted to the stainless steel top plate. It is true that disturbing the platter/bearing will stretch the drive belt, BUT, this does not occur during normal operation and the belt is intended to filter out any motor vibration from reaching the platter.

I, personally, think that counting platter revolutions over three minutes and getting to 99.6 is pretty damned good. However, consider buying a cheap tachometer that will measure in the right range for greater accuracy.

Given the age of the turntable (1983-4) and the assumption that it still has its original motor, it is quite likely that the motor is now showing its age and is either in need of lubrication or is worn out, or both. I assume that the Valhalla was serviced and adjusted by a reputable repair tech.

‘troll
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2018-03-06, 22:36
Post: #4
RE: LP12 platter speed
https://forums.linn.co.uk/bb/showthread....ight=tools
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2018-03-06, 22:47
Post: #5
RE: LP12 platter speed
also might be worth just using a strobe light app on a smartphone. Usually free and gives you an accurate 50Hz strobe and just print a linn timing disc. Pretty good for cheap home set up.

strobe

LP12, Kore, Cirkus, Akito, Goldring 2100. KDSM, Solos/D, 242s/2
QNAP TS269, SONOS boxes around the house.
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2018-03-07, 08:59 (This post was last modified: 2018-03-07 08:59 by smokestack.)
Post: #6
RE: LP12 platter speed
The fact that the platter can move on the suspension relative to the motor position actually improves speed stability because that flexibility helps compensate any small inconsistencies around the circumference of the belt.
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2018-03-07, 10:00
Post: #7
RE: LP12 platter speed
Thank you to ContinentalTypeR, Moomintroll, Glyn Ruck, SewellRG and Smokestack for your various helpful pieces of information.
I now understand things better. When I repeated my experiment but with the outer platter in place I could see that the sub-assembly moved swiftly back into position relative to the motor, and I think I know why. The bounce remains good, the cartridge and arm track OK, so I will leave things alone.
I am so glad I asked the question here before doing anything!
Regarding platter speed, I have done a strobe test (should have realised there would be an app!), which confirms the platter is running somewhere around 0.3/0.4% slow. I don't know that I could hear the difference if it was perfect, so I will live with this for the time being.
The noises probably are due to an aged motor, which is on my list of upgrades. However I will ask that the lubrication be checked when I get a new cartridge fitted later this year.
Thanks again.
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2018-03-07, 10:08
Post: #8
RE: LP12 platter speed
(2018-03-06 18:42)moomintroll Wrote:  Hi Nick,

Firstly, you’re misinterpreting Peter’s meaning or reading it out of context. At that point in the guide, he’s talking about fitting the subchassis. Once the subchassis is positioned over the suspension bolts, you have to very careful not to knock it against the bolts, as you could knock them out of true, or damage the subchassis (more important if it’s a high value Keel). All he’s saying is that, once the grommets and springs are fitted, the subchassis is no longer free to drop or bang against the bolts. What he’s NOT saying is that it is locked in place and unable to move!

Given the age of the turntable (1983-4) and the assumption that it still has its original motor, it is quite likely that the motor is now showing its age and is either in need of lubrication or is worn out, or both. I assume that the Valhalla was serviced and adjusted by a reputable repair tech.

‘troll

Thanks for fielding this troll, I'm not visiting these parts much at present due to work and family pressures, so your interception is much appreciated Smile Yes the LP12 would be upside down in the jig at this point:
Quote:Me: Once the springs, grommets, washers and nuts are fitted then the sub-chassis can no longer move about freely. This is good as soon the deck will be turned the right way up again. However, not before the fitting of the cross-member, otherwise known as the wire strap to the plinth.

For the moment, anyone with questions is always welcome to PM me as I get an email reminder of course. Hopefully I'll be contributing more before too long.

KR

Peter

Fettling LP12s since 1980 and member here since 2008
Tel 0333 200 4475
Email - peter@cymbiosis.com
Skype - peteratcymbiosis
Facebook - www.facebook.com/Cymbiosisaudio/
www.cymbiosis.com
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2018-03-07, 10:28
Post: #9
RE: LP12 platter speed
(2018-03-06 18:42)moomintroll Wrote:  I, personally, think that counting platter revolutions over three minutes and getting to 99.6 is pretty damned good. However, consider buying a cheap tachometer that will measure in the right range for greater accuracy.

Given the age of the turntable (1983-4) and the assumption that it still has its original motor, it is quite likely that the motor is now showing its age and is either in need of lubrication or is worn out, or both. I assume that the Valhalla was serviced and adjusted by a reputable repair tech.

‘troll

Yes, there are many different ways to measure speed but hopefully one can arrange to visit your Linn Specialist Retailer and have the whole deck checked over/set-up - Always worthwhile Smile

I use one of the Linn Strobes, sadly no longer available from HQ.

[Image: goZqHs.jpg]


KR

Peter

Fettling LP12s since 1980 and member here since 2008
Tel 0333 200 4475
Email - peter@cymbiosis.com
Skype - peteratcymbiosis
Facebook - www.facebook.com/Cymbiosisaudio/
www.cymbiosis.com
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2018-03-07, 10:54
Post: #10
RE: LP12 platter speed
(2018-03-07 10:28)Cymbiosis Wrote:  
(2018-03-06 18:42)moomintroll Wrote:  I, personally, think that counting platter revolutions over three minutes and getting to 99.6 is pretty damned good. However, consider buying a cheap tachometer that will measure in the right range for greater accuracy.

Given the age of the turntable (1983-4) and the assumption that it still has its original motor, it is quite likely that the motor is now showing its age and is either in need of lubrication or is worn out, or both. I assume that the Valhalla was serviced and adjusted by a reputable repair tech.

‘troll

Yes, there are many different ways to measure speed but hopefully one can arrange to visit your Linn Specialist Retailer and have the whole deck checked over/set-up - Always worthwhile Smile

I use one of the Linn Strobes, sadly no longer available from HQ.

[Image: goZqHs.jpg]


KR

Peter

I am already in contact with my local Linn dealer (who did the service last year), and will ask them to re-check the motor etc. when I go to get a new cartridge.
Thanks
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