View Full Version : SME 3012 mounting distance
Wakefield Turntables
10-12-2012, 20:39
I Have a SME 3012 mk 2. Am I correct in thinking the mouting distance from the top of the bearing spindle to the top of the tonearms apex is 292.2mm. I finally getting around to making the stone plinth for the 301 and want to get the design perfect.
The brochure at VE says 11,58" (spindle to bedplate centre)
that's 294,1mm...
http://www.vinylengine.com/ve_downloads/index.php?sme/sme_series2_brochure.pdf
Unless I misread something, where did you get your info from?
Wakefield Turntables
10-12-2012, 21:23
The vinyl engine tonearm specification PDF file. For the Mk1 they quote 308.8mm, the Mk2 292.2mm and the 3012R 295.6mm I have the mk2 (I THINK!). I think I need to get a picture up of what I've got, but that will have to wait until tomorrow.
Wakefield Turntables
11-12-2012, 09:31
Great :rolleyes: that's now three values I have, is there no consensus of opinion. Barry where did you get your value:cool:
For the Mk1 they quote 308.8mm, the Mk2 292.2mm and the 3012R 295.6mm I have the mk2 (I THINK!).
I thought there were 4 types...
The I
The II
The II Improved
and the R
Great :rolleyes: that's now three values I have, is there no consensus of opinion. Barry where did you get your value:cool:
From http://www.audioasylum.com/cgi/t.mpl?f=vinyl&m=988653. I wouldn't worry about a diference of 0.6mm - that's the whole point of having a sliding bed plate.
However I have to confess the platter spindle to bedplate centre distance (D) quoted is such for assumed null points of 66mm and 121mm; that is Baerwald's geometry.
I suspect the SME 3012 Mk.II was designed to follow Stevenson's geormetry, for which the null points are 60.3mm and 117mm (certainly the alignment protractor has a null point at 60.3mm).
The arm mounting distance can be calculated from these values; see http://theartofsound.net/forum/showthread.php?t=20109 (equation 18). L is the effective length of the arm; in this case 294mm. With these figures, I calculate D = 281.75mm.
Regards
John Gordon
11-12-2012, 12:48
The effective length is 308.8mm not the mounting distance. Mount the base such that the centre of the slot is at around 295mm. This isn't critical, and there is no need to be worried about it. The SME has an adjustable base so that you will alter the mounting distance anyway as you set the alignment. See here (http://odysseytonearms.blogspot.com.es/2011/04/sme-geometry.html) for more info on SME Geometry.
John
Rare Bird
11-12-2012, 13:37
The arms effective length minus the optimum over hang equals the mounting distance.
The effective length is 308.8mm not the mounting distance. Mount the base such that the centre of the slot is at around 295mm. This isn't critical, and there is no need to be worried about it. The SME has an adjustable base so that you will alter the mounting distance anyway as you set the alignment. See here (http://odysseytonearms.blogspot.com.es/2011/04/sme-geometry.html) for more info on SME Geometry.
John
Useful as that website is, the reference to the 12" SME arm is only for the SME V-12 arm.
The OP was enquiring about the original 3012 arm. This should not be confused with the later 3012R arm, or the V-12 arm.
Rare Bird
11-12-2012, 17:51
Thats right Barry the '3012R' is mounted at 295.6mm
Not sure if Andrew's question has been answered to his satisfaction - but I have been 'worrying at it' like a dog with an old bone.
To my annoyance, I have mislaid the mounting the template for the SME 3012 arm. However I have measured the mounting distance (spindle-to-arm pivot) for my sample (mounted on a TD124/II). The distance to the centre of the bedplate is 294mm (to within 1mm).
I also measured the stylus to pivot distance (the effective arm length). When fitted with a Shure cartridge (who adhere strictly to a stylus-to-mounting point distance of 9.5mm +/- 1mm), the distance is 316.5mm. This implies the distance from arm pivot to cartridge/headshell fixing holes is 307mm.
VinylEngine quote this distance to be 305mm (12" = 304.8mm) and the arm mounting distance to be 294mm.
Given the difficulty in accurately measuring the stylus to pivot distance, VinyEngine's figures are believable.
I mentioned that I believe the Mk.II SME arms were designed to follow Stevenson's geometry. This sets the two null points at 60.325mm and 16.992mm. From this, given an effective arm length of 305mm, the arm mounting distance will be 293mm; very similar to the 294mm quoted. Likewise an effective arm length of 307mm, leads to a mounting distance of 295.3mm
Any such small error is easily catered for by the use of the sliding bedplate, and certainly the important null point of 60.325mm will be achieved.
That wraps up things neatly (I hope).
John Gordon
13-12-2012, 01:11
Hi Barry,
I should have made it clearer on the blog that the explanation was relevant to all the SME arms.
Because whether the arm is a V12 or a 3012 of whichever version, the issue of precise measurement of effective length and mounting distance is a red herring. The principle of the SME using the sliding base means that the effective length is actually that, i.e. it is effected by the cartridge.
Different cartridges give different effective lengths. This is compensated for by adjusting the base, thereby achieving the pivot to spindle distance for the given alignment.
The mounting distance for the base plate merely has to be within a few millimetres, close enough to allow the sliding base to do its job. In other words, you could mount any of the 12" arms on a cutout for any of the others and still be able to achieve a chosen alignment, whether Lofgren A or B or Stevenson.
Which is why I was saying there is no need for anyone to worry about it unduly.
John
Wakefield Turntables
13-12-2012, 09:00
I'm at work at the moment but will be giving this topic some attention to detail tonight when I get some time, I'll post some pics as well :cool:
Rexton, what do you mean by 'apex' out of interest? To me that means the top point of something - does it have a specific meaning in terms of tonearms? I'm often lost by technical jargon with tonearms and set-up.
I'd have have also thought that the whole idea of the sliding base was to adjust the effective length and the amount of movement is such that you have a +/- of about 20mm. You only need to be within this, taking into account the range of cartridges (and associated headshells) you might use. Id guess that say an SPU headshell would be deliberately the same length as a regular SME one but you never know..
Be careful with your photos as it might get the thread moved into the smaller idler forum and so less views (and potentially either slower responses or a narrower sample of replies !)
Hi Barry,
I should have made it clearer on the blog that the explanation was relevant to all the SME arms.
Because whether the arm is a V12 or a 3012 of whichever version, the issue of precise measurement of effective length and mounting distance is a red herring. The principle of the SME using the sliding base means that the effective length is actually that, i.e. it is effected by the cartridge.
Different cartridges give different effective lengths. This is compensated for by adjusting the base, thereby achieving the pivot to spindle distance for the given alignment.
The mounting distance for the base plate merely has to be within a few millimetres, close enough to allow the sliding base to do its job. In other words, you could mount any of the 12" arms on a cutout for any of the others and still be able to achieve a chosen alignment, whether Lofgren A or B or Stevenson.
Which is why I was saying there is no need for anyone to worry about it unduly.
John
I quite agree John. My concern was the propagation of errors by VinylEngine.
As you say the the effective length is dependant on the cartridge used. It is only recently that cartridge manufacturers have adopted the IEC standard of 9.5mm +/-1mm stylus to fixing distance. All current SME arms assume this figure when the effective arm length is quoted. Before the 'effective arm length' quoted was the distance between the arm pivot and the centre of the cartridge fixing holes in the headshell; which is incorrect.
My interest was to see how close these dimensions fitted arm geometry theory. As you, and others, have rightly pointed out this is somewhat academic - the provision of the sliding bedplate allows some 40mm of adjustment to achieve the correct overhang.
In my opinion the use of a sliding bedplate is the best way of doing things, provided you don't change cartridges too often.
Finally I do believe the 3012 arm geometry follows Stevenson, so the correct null points to use on an alignment protractor are 60.3mm and 117mm, not those marked for Baewald's geometry (66mm and 121mm).
Regards
Wakefield Turntables
13-12-2012, 20:25
Ive not had as much time as i would like to assess the various areas of geometry for the 3012 alignment but i have included a photo of my idea of what constitutes the mounting distance between the apex of the spindle in the bearing and the apex of the tonearm column which according to various sources should be bewteen 295 and 297mm for a SME 3012 v2. I have not checked which geometry the 3012 should be aligned to (stevenson baerwold etc). Currently my 3012 is setup at 300mm mounting distance, and I cant seem to align the cartridge to either Baerwold or Stevenson using Dr. Feckhart protractor. My SME V aligns perfectly to Baerwold when using Feckhart. I will hopefully be spending some more time modifying the plinth and i will add some more photo's when I get some time tomorrow. Any more comments would be greatly welcome. Thanks guys.
Rare Bird
13-12-2012, 21:33
Andy
PM to put your mind at peace. ;)
With your mounting distance of 300mm, do you find the arm base needs to be moved closer to the platter spindle in order to achieve zero tracking error at 60.3mm?
I find it hard to believe that 5mm should make such a difference.
Wakefield Turntables
14-12-2012, 11:25
Barry,
If you look carefully at the picture the tonearm is pushed right upto the end of the mounting spacer and that's at 300mm so I think I have cut the mounting section a little too far away from the spindle Apex :doh: I have an afternoon off today so I'm going to try and make some head way with this. I'll post some pics if I get chance.
Andy
I've just looked at your photo. Yes, it is as I suspected - the arm mounting slot, at 300mm, is too far from the platter centre. The arm is hard up against the bedplate (nearest to the platter spindle).
You need to reposition the bedplate a little closer to the platter centre, so you can achieve the correct overhang according to Stevenson's geometry; that is, with null-points at 60.3mm and 117mm.
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