Sansui SR-636 alignment adventures

[Vintagear]

Below are my photos - all this can be a bit inaccurate, but it does seem that my tonearm with the headshell is slightly longer than yours.
That is interesting and I wonder what is the reason.

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There is a screw on the bottom end of the tonearm wand where the aluminum wand slides into the thicker support that is part of the fulcrum/gimbal assembly. I believe that screw attaches and holds the wand in place. I wonder if somehow your wand is not set in all the way. That's the only thing I can think of that would add length to the arm itself other than the arm being bent outward slightly.

If you have a standard ruler try the other measurement I made just to see if you get approximately what I get. If the base is in the same spot then the issue is definitely narrowed down to the tonearm length.

 

[PiotrekN]

There is a screw on the bottom end of the tonearm wand where the aluminum wand slides into the thicker support that is part of the fulcrum/gimbal assembly. I believe that screw attaches and holds the wand in place. I wonder if somehow your wand is not set in all the way. That's the only thing I can think of that would add length to the arm itself other than the arm being bent outward slightly.

If you have a standard ruler try the other measurement I made just to see if you get approximately what I get. If the base is in the same spot then the issue is definitely narrowed down to the tonearm length.

I don't have a ruler wide enough to measure that other distance, the narrow ruler does have support points when it is inserted there.
However I do agree that the installation of the wand might be the only reasonable explanation. The problem is, I am not sure I want to experiment with it, and even if I wanted the access to that screw seems very limited. I need to think how much this influences the geometry of the tonearm and if it is worth the hassle.
I got my 636 a couple of years ago, if the wand was indeed moved then it could have happened at any earlier point by someone servicing the tonearm.

 

[Vintagear]

I don't have a ruler wide enough to measure that other distance, the narrow ruler does have support points when it is inserted there.
However I do agree that the installation of the wand might be the only reasonable explanation. The problem is, I am not sure I want to experiment with it, and even if I wanted the access to that screw seems very limited. I need to think how much this influences the geometry of the tonearm and if it is worth the hassle.
I got my 636 a couple of years ago, if the wand was indeed moved then it could have happened at any earlier point by someone servicing the tonearm.

Yeah I probably wouldn't mess with it either, plus I think you'd have to remove the tonearm to get to that screw anyway. One thing I might do if it were me is (very carefully) hold the base and ever so gently push the wand in (without squeezing it) to see if there is any loose play.

Otherwise, just enjoy that 636!

 

[PiotrekN]

So just as an update, I double checked everything. The measurement of the length of the tonearm is actually quite tricky to do and upon trying to do it a couple of more times I realized very small movement at the supposed pivot point can give different results. After redoing it my tonearm seems to be of correct length after all, but I don't feel confident this measurement can be done precisely, especially that the exact location of the pivot point involves some guesswork.

I rechecked the protractor again, all lengths were measured with a ruler precise up to 0.1 mm: the three lines on the photo intersect at exactly the same point - the pivot - and are at distance 230mm from the arc.
Verified overhand pf 16.1mm and the distance to the null points. It is all as in the specs.




Then I've rechecked the alignment - the following three pictures are taken at the outer edge, between null points and at a point close to the spindle. Photos were taken with a macro function, approximately along a line tangent to the arc at point where the stylus is placed, to ensure proper perspective and that the stylus sits perfectly on the arc, and even at the same position within the arc (i.e., at the middle of the printed arc).






As a side comment to anyone who has not used an arc protractor before, the procedure to adjust overhang using an arc protractor is as follows.

Take the tonearm as close to the spindle as possible and move the arc protractor so that the stylus sits perfectly on the arc.
Now, without moving the protractor move the arm all the way to the outer edge of the platter and lower the tonearm.
If the stylus lands behind the arc (i.e. to the right of the arc when looking from the front of the TT) the cart needs to be moved back in the headshell; and of course if it lands in front of the arc then the cart needs to go forward.
After moving the cart repeat the whole procedure. Adjust until the arc can be traced perfectly by the stylus from the outer edge to a point as close to the spindle as possible.
The pivot-to-spindle line should point directly at the pivot.
At the null points the alignment should now be automatically correct.

In any case this is what I have, I don't think this can be realistically done much better. The stylus tip is still approximately 1.5mm behind the mark on the headshell.
By the way, I printed another version of the protractor with the two extra arcs for the two Lofgren alignments, these can be seen above.
I also wanted to do the same for the Stevenson, but as expected, the difference in the overhang between the Sansui geometry and Stevenson for this tonearm is too small (0.15mm) and the two arcs are so close together that they just make one fat arc.

 

[PiotrekN]

Here is one more thought: as I mentioned in the first post, the specs for both SR-636 and SR-838 have a quite serious mistake:
they give the overhang in both mm and inches, however the values in different units do not agree.
We have 16.1 mm and 11/16"=17.46mm. Below is an excerpt from the Sansui SR-636 brochure, however this mistake is repeated in all published materials on either of these turntables that I have seen.



The numbers for the effective length match, so I think this value can be considered to be certain.

So which overhang is the correct one? 16.1mm or 17.46mm (or probably 17.5 if it would indeed be an official spec)?

Below are two distortion diagrams assuming 17.46mm overhang, 22.5 offset angle and two different mounting distances:
213.9mm (agrees with 16.1mm overhang and 230 effective length) and 212.54mm (agrees with 17.46mm overhang and 230mm effective length).
In both graphs it is clear that it would be hard to choose worse alignment (unless one changes the offset angle by twisting the cartridge in the headshell), so it is highly unlikely this would be the official Sansui alignment scheme.

My theory now is that in the manufacturing of the headshell the mark for setting overhang was erroneously positioned using the 11/16" spec.
The difference is approx. 1.4mm which would perfectly explain the discrepancies I pointed out earlier in this thread.

 

[matcardozo]

Hi, I'm new to the forum, and I'm here to revive this thread with some questions about compatibility between the Sansui SR-838 tonearm and the Shure M91G cartridge.

I purchased the turntable a couple of months ago, and to my frustration, I have not been able to get rid of the tracking problems on cartridges with elliptical styli. I have both a Shure M91G (with aftermarket stylus) and also an Ortofon Omega (with original stylus), both with tracking weights between 0.75-1.5 grams (Shure) and 1.5-2 grams (Ortofon) and the problem is that both have skip issues at different points of my records, even on records in mint condition and washed in my Spin-Clean system.

The turntable uses the original headshell and with both cartridges I have tried both the Stevenson and Löfgren-A alignments, without good results. I also tried the protractor designed by @PiotrekN, even the famous "shortcut" of 53mm according to the manufacturer's guidelines. All this without getting either of them to play music without errors.

Curiously, the only cartridge I can listen to music with on this turntable is a Stanton 680, with a tracking force of 2-5 grams, but that uses an aftermarket (DAL6800) spherical profile stylus.

I have seen videos of the SR-838 working without problems with the "newer" Ortofon 2M Red cartridges (with elliptical stylus) and 1.8g tracking force, so it makes me think that the problem might be in the weight of the cartridge body: Shure, 5.6 grams; Ortofon Omega, 5 grams. Although it should be noted that the SR-838's tonearm range supports cartridges from 4 to 11 grams without needing its sub-weight. All in all, the cartridges mentioned work without any problem on the Technics SL-2000 that I used before acquiring the SR-838.

And yes, I've tried a different headshell too, with same results.

So, to sum up: is it a problem with "audiophile-grade" elliptical styli with very low tracking force or very light body (noting that the 2M Red has a mass of 7.2 grams in total)?, or is it a problem of compliance between the tonearm and my cartridges?

I am attaching photos of the various unsuccessful attempts to make the Shure M91G work despite being, from my point of view, well aligned with the different configurations.

Any type of feedback will be highly appreciated.


Shure M91G aligned to Stevenson's protractor


Shure M91G aligned to Stevenson's protractor - Front view


Shure M91G aligned to Löfgren's protractor



Attempting to align my Stanton 680 to @PiotrekN custom protactor that finally worked

 

[CrSens]

Are you using anti-skating at all? On one picture the weight is visible at minimum position. On a couple of pictures azimuth is off (needle is not perpendicular to record). These things might matter for skipping, but they might not, too. I've seen one 636 where tonearm seemed rattled and somewhat loose, and it was skipping. The cartridge weights are fine, but I would not trust aftermarket Shure N91G to track at 1.5g.Not even close to that. Unless it is Jico.

 

[matcardozo]

Are you using anti-skating at all? On one picture the weight is visible at minimum position. On a couple of pictures azimuth is off (needle is not perpendicular to record). These things might matter for skipping, but they might not, too. I've seen one 636 where tonearm seemed rattled and somewhat loose, and it was skipping. The cartridge weights are fine, but I would not trust aftermarket Shure N91G to track at 1.5g.Not even close to that. Unless it is Jico.

Yes, on photo 4 the antiskate weight is at its maximum of 2.5 grams for the Stanton cartridge, just out of frame.
About azimuth, that's how that Stanton stylus sits, but that cartridge is ok. As I see it, the M91G is sitting perpendicular to record (photos 1 to 3), and same with the Ortofon Omega.
Tonearm VTA has been checked too, and it sits parallel to the record while playing.
I considered the M91G aftermarket stylus factor in the equation, but the Ortofon Omega has an original needle that is skipping too
And both of the elliptical styli work fine with their recommended tracking force (Shure: 1.25g; Ortofon: 1.75g) on my 2 other tables, a Technics SL-2000 and a JVC QLY-3F.

 

[CrSens]

The tonearm is defective, nothing to do with the alignment. In good condition this tonearm works with wide range of cartridges, especially with aftermarket headshells (the original one is quite heavy, and reduces the range of usability).
If in doubt, ask the question on the turntable forum, the place is full of experts you can exchange your wits with the whole day.