Feickert analogue protractor....Owners impressions

Hi Smoffatt,

For an SME or a Schroeder (Reference and DPS), I'd use either a conventional, two-point protractor and sweat through the details, or alternatively I'd figure out the effective length for my favorite cartridge and order an arc-style protractor for that combination.

I'd obviously hope to live with that cartridge for quite some time if I committed to this solution.

Frank Schroeder has observed a statistical norm for stylus position centering around the stylus landing 9.25 mm in front of the cartridge mounting bolts (from his tonearm manuals). SME might presume a number slightly different than this to arrive at their specified effective length.

Your XV-1s cartridge comes in at 8 mm (from the engineering drawings on the Dynavector website). From SME's website, the Model V has an effective length (pivot to stylus) of 233.15 mm. We'll hang onto this number as a reality check.

I'd get my ruler out and draw a line connecting the two cartridge mounting bolts and then measure 8 mm forward of this line to see where the XV-1s stylus lands. I'd then measure the straight-line distance from the center of the bearing pivot to this stylus position I drew. This is your effective length. Perform a reality check against the 233.15 mm specification. You shouldn't be too far off from this, and likely a mm or two shorter than 233.15 mm.

Now, here's where it takes commitment (as in dollars). You're faced with ordering a protractor for this effective length. Assuming you got it right, you now have a protractor for one tonearm and one model in Dynavector's cartridge line (double ouch).

There's one other challenge with the SME V. Not only can't you change the effective length (it has mounting holes, not slots), but you can't vary the offset angle by much - only by whatever play there is in the headshell holes. Some people (another thread) have reported that they've opened up the holes in their headshell slightly - to permit some offset angle adjustment.

If it were me, I'd probably keep with the two-point affair and sweat through the process - assuming I didn't have access to a drawing tool which allowed me to try a variety of effective lengths for the cost of a few pieces of card-stock paper.

The thought of being wrong in my measurements (described above) would likely freeze me in my tracks - ordering without feeling comfortable that I measured the effective length with enough precision.

Thanks for the comments, Stiltskin. I find these conversations to be productive for all concerned. Every time I try to describe something, I think about it slightly differently and learn something. If I only had more time for this.

Cheers,
Thom @ Galibier

Typo - I meant to type 206.5 on the table\arm that needed 210mm.. It's late..goodnight.

Joe

Tom - I'm probably gonna display my ignorance here so kindly bear with me regarding the SME, ... if the stylus perfectly traces the arc in a Wally or other arc-style protractor, why does it matter that you can't change the overhang because of no slots in the headshell? With my SME V on a Teres I can set up different carts with the same Wally.

(And SOA may be a lifestyle choice for some, but its still a Gartner product living out its own cycle of hype - one man's abstraction layer is another man's pot of beans. :-)

Tim
 

Hi Tim,

I may have to check out of this thread for a few days ... The short answer is that if you trace an arc (Wally, etc.), then life is good.

A while ago, I performed an extreme-case analysis of using the wrong arc on paper. I've not yet had the opportunity to try this out. I created situation which will never occur in real life - describing three arcs for a Triplanar:

a) a 239 mm effective length - the arc created by a cantilever which is 11 mm too short - in effect a negative cantilever length
b) the intended 250 mm effective length - the nominally correct arc
c) a 262 mm effective length - an arc created by a cartridge whose cantilever is 12 mm too long

http://www.galibierdesign.com/images/Protractor_Alignment_Exercise_01.pdf

The idea was to "pretend" that the Triplanar had no mounting slots, and that the user would try to align a cartridge in scenarios "a" and "c" whose stylus positions resulted in a too short and too long effective length - changing the pivot to spindle distance (11mm closer and 12 mm farther for "a" and "c", respectively).

The owner of this nominally correct, 250mm arc protractor would try to land the stylus somewhere on its theoretical arc. In use, the only adjustment available to him would be a pivot to spindle distance compensation.

You can see that even in these extreme (and well beyond real world situations), the arcs traced by "a" and "c" are fairly close to the ideal arc. Now, we're told that you need to get to better than 0.5mm of the specified pivot to spindle distance (not the arc, the pivot to spindle distance), and in these examples we've diverged by 12 mm and 11 mm respectively.

So, the question (back to reality here) is that just because we've failed, how much better is our setup (if at all) than that which we can achieve with a two-point protractor? I suspect that our audible results in a real-world error (e.g. a cartridge which diverges by only 1 or 2 mm) would be such that most of us would achieve a better setup with an arc-style protractor (better than with two-point, but not as good as ideal).

I've been planning on verifying this by making up two arc-style protractors for my Triplanar to mimic the SME/Schroeder situation - a stylus whose cantilever is, say 2 mm shorter as well as 2 mm longer than anticipated for the arm's specified effective length - yielding effective lengths of both 248 mm and 252 mm (vs. the 250 mm for the Triplanar).

I'll report back on this, but it may take some time. It will take some long-term listening to get the grok on any differences. Unfortunately, I can't measure the distortion, so this would be a subjective experiment which will take some time. My guess (to be verified) is that these errors will result in less than perfection, but somewhat (on average) better than most of us can do with a two-point protractor (Frank Schroeder and Doug Deacon notwithstanding).

It wouldn't hurt to perform a visual check with a two-point protractor - to see if (upon adjusting with the "wrong" arc protractor) whether we'd consider the setup good enough if we were using a two-point protractor. I suspect that most of us would.

Yes, SOA ... yet another three letter acronym which makes me want to retire to a cabin in the woods (with, of course, Solar PV panels to run my hi-fi with). I think the usability question is a good one of course. All too many geeks in both IT as well as hi-fi lose track of the problem they're trying to solve and get lost in their egos - building more and more complex mousetraps.

Cheers,
Thom @ Galibier

Hi Joe55ag,

Basically, you stepped back analyzed the problem, and came up with a workable solution. Good for you!

Take note of how Joe approached this problem.

You bring up the very good point that, just because a manufacturer specifies certain paramaeters, you are not limited to this and can create your own.

Stated another way, if you're "stuck" with a certain pivot to spindle distance because of tonarm mounting circumstances beyond your control, you may well be able to still achieve (say, Baerwaald) alignment by adjusting the position of the cartridge in the headshell (fore and aft as well as offset angle).

Of course, in your case you ran out of headshell slot, but your approach was still one of "what set of parameters will work if I'm stuck with one that I can't change?".

Cheers,
Thom @ Galibier