Tonearm measurements on a Thorens confusing me!

[pedalhead]

Hi all,

First thing, please excuse my ignorance but I'm rather new to this vinyl malarkey :). I picked up a really nice minty TD125 mkII this week and I'm trying to work out which arm to put on it (it came with an SME cut board). After some chat with the super helpful @petrat, I now have the SME M2 in mind. However, I'm rather confused as to whether the M2-9 or M2-10 would be suitable.

Here are a couple of examples of TD125 fitted with M2-9...

http://www.theanalogdept.com/images/spp6_pics/Thorens_Gallery/JH_Canada/JH_0104.JPG

http://vinylnirvana.com/wp-content/uploads/01915-600x450.jpg

It seems to me that on both of those decks, the SME M2-9 is mounted quite far to the left on the arm board (more than usual for, eg a 3009). Which leads me to think, perhaps the M2-10 would be a better fit on the TD125. However, looking at the numbers on the vinylengine database has confused me...

Pivot > Spindle (mm)
3009 II = 215.7
M2-9 = 215.4
M2-10 = 222

Looking at those figures, it looks like the M2-9 would be a direct swap for a 3009 (as you'd expect)...but, pictures of the 3009/TD125 combo always show the 3009 sitting centrally on the arm board. To confuse matters further, I've also seen data claimed to be from SME themselves that quotes the SME 3009 TT to arm pivot as 221.80mm (which would match the M2-10). This is far more consistent with the visuals I've seen, but I find it hard to believe that the vinylengine database is wrong for the 3009 (?). Furthermore, the centre of the SME cutout on my arm board measures pretty much spot on 222mm, again a match for the M2-10.

Muddying the waters further, another arm I'm considering is the Jelco 750D. Vinylengine quotes that arm as having a 214mm pivot > spindle, more in line with the 3009 and M2-9, BUT that seems to mount centrally on the TD125 arm board as well, as on this lovely thing...

http://stuartlittlejohn.f2s.com/TD125_1.jpg

I considered it might all be to do with overall length of the arm, but again the numbers don't see to bear this out. I'd hugely appreciate any thoughts on what's going on here please, and ultimately, which SME M2 arm is more suited to the TD 125 mkii. Thanks!

[Barry]

As far as I know, the adjustment range for the SME bedplate is +/- 1/2" (12.7mm), so if your arm mounting slot is cut on a true radius (and many aren't), then in principle you could, at a pinch, use either arm length.

Vinylengine.com is not error free. I would check with SME for the correct TT spindle to arm pivot length. Don't be mislead by stock photos: I have several arm boards cut for 9" SME arms for my Thorens TD124/IIs, and all have the arm mounting slot cut in slightly different positions.

If 222mm is the correct distance for the SME M2-10, then you have already answered your own question. Were it me, I would go for the M2-10, provided the stylus does not lay too close to the front edge of the TT, otherwise there is a risk you could accidentally 'snag' and damage the stylus/cantilever.

[Barry]

Looking at the SME website: http://www.sme-audio.com/tonearms/sme-series-m2-tonearm ,

the arm pivot to TT spindle distance is 215.4mm for the M2-9 arm and 222.0mm for the M2-10. So the figures quoted by vinylengine.com are correct and your own armboard is correctly cut for the M2-10 arm.

[pedalhead]

Thanks Barry. I'm just a bit confused because this 125 had a 3009 S2 on it, but it looks like the arm board wasn't cut optimally for it. Oh well. Cheers!

[Barry]

Thanks Barry. I'm just a bit confused because this 125 had a 3009 S2 on it, but it looks like the arm board wasn't cut optimally for it. Oh well. Cheers!

That would seem to be the explanation. The adjustment range (+/- 12.7mm) of the SME bedplate is generous, so one can usually achieve the correct overhang, even if the bedplate slot is not quite in the right place.

As I mentioned I have several armboards cut for 9" SME arms for my TD124s, and all of them have the slot in slightly different positions. Some have the slot cut parallel to the edge of the TT, others are cut to lay on a near radius (it is not possible to have the slot laying on a true radius with the 124). To attain the maximum overhang compass, the slot does need to lay on a true radius, but for most cartridge/headshell combinations, the correct overhang can be achieved even if the slot is not on a true radius.

[pedalhead]

Good to know, thanks Barry. Hope I'm not too late for a pre-price rise SME M2-10!

[CornishPasty]

Get your tape measure out and see what distance you've got between the spindle and the centre of the SME cutout.

[Barry]

Good to know, thanks Barry. Hope I'm not too late for a pre-price rise SME M2-10!

Should be a nice combination Mark, both in performance and aesthetics. Let us know how you get on, and of course we will want to see some photos! :)

[pedalhead]

Absolutely, cheers :D

[pedalhead]

Get your tape measure out and see what distance you've got between the spindle and the centre of the SME cutout.

Thanks Ralph. As above, 222mm spindle to centre of the cutout on my board, which coincides with the M2-10.

[CornishPasty]

Jobs a good 'un then. The M2-10 is a nice tone arm.

[killie99]

You can mount the arm pretty much anywhere you like on the armboard (within reason, no point in mounting the arm at an extreme point of the armboard) so long as you have the pivot to spindle distance correct - left, middle or right - you could even mount it at the bottom of the armboard if you wanted with the arm pointing out to the left. I experimented with several positions and settled on the aesthetically pleasing centre line position (that's my TD125 you linked to in your post,here's a more up to date pic) so I wouldn't worry too much about it so long as you can align the cart. The huge advantage of the SME arms is the amount of travel you get with the bedplate so you don't have to cut the hole very accurately at all - as you have found with the different armboards you have looked at. Not sure why other arm companies haven't used this technique.

http://stuartlittlejohn.f2s.com/125_1.JPG

[pedalhead]

Beautiful TT, Stuart! I just this morning ordered an M2-9 from Dave @ Sound Hifi at an excellent price. He still has a few more at pre-rise prices if anyone is interested. I was surprised to hear that the M2-10 and 310 are being discontinued, and actually I'd pretty much decided that I'd rather get the M2-9 over the M2-10 anyway simply for resale value apart from anything else. As you say, the adjustment available with the SME bed plate means it'll probably work out fine on my deck, and if it doesn't then I can just make up a new arm board, no big deal.

Another tick in the box of my boyhood hifi dreams, a nice TT with an SME arm :)