Feickert analogue protractor....Owners impressions

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

Oh yes ... a quick follow-up to Joe.

Yes indeed, someone could easily order an arc that resulted in a 222.8 mm pivot to spindle distance.

Typically, you work backwards from effective length, but if you use John Ellison's wonderful spreadsheet and set the precision level to 4 decimal places, you can (using binary search techniques) derive any number you need in 5 or 6 tries.

Once you have an effective length, tell Yip (Mintlp) or Wally what you need and in 3 weeks (Yip) or ??? (Wally), it's in your mailbox.

It's all just computers and numbers and one number (222) is as good as another (222.8).

Cheers,
Thom @ Galibier

Smoffatt - the best way to get a cart aligned in an SME V, imo, is with a Wallytractor. I haven't seen the Mint, but if its the same design and quality as a Wally, then it will work as well. For me, the arc style protractor is much easier than a two-pointer, but those can work. (Say what you will, Wally deserves a boatload of credit for bringing his mirrored arc style tractor to us audiophiles - like many others on this forum, he's a generous contributor to our hobby.)

The fine gradient movement of the SME's sled makes small adjustments simple to dial the stylus in the arc across its length - much easier than manually shifting the cartridge in head shell slots and then tightening the cartridge bolts without changing anything. This, imo, is one of the design's real strengths. Once the tone arm is mounted, the sled makes pivot-to-spindle distance somewhat of a moot point.

If your cantilever (and ultimately your stylus) is at right angles to a line drawn through the headshell bolts, then there should be no need for cartridge adjustment to hit the proper offset on the protractor's grid lines. Otherwise the soft head shell metal makes it simple to *very slightly* enlarge the holes in the headshell enough for minor adjustment. (I did this turning a drill by hand - let me know if you need the bit size, I've got it somewhere in my notes at home.)

Tom - thanks for the follow-up!

Tim

Tim,
"The fine gradient movement of the SME's sled makes small adjustments simple to dial the stylus in the arc across its length"
Wouldn’t you be defeating the purpose of a custom protractor by changing the spindle to pivot distance as an adjustment? If you order a protractor for SME isn't the arc based on the 233.15 spindle to pivot distance, the distance you change to adjust? I bring this up because you mention that the Wally is the best method for SME alignment(IMO), I'm not sure it or any arc protractor is unless the cartridge one uses produces the correct effective length for the 233.15 arc. I just mounted a SME IV.Vi so I'm looking for feedback also. Now, if I measure the effective length and back into the spindle to pivot measurement and it's not the SME suggested 233.15, I wonder if it would be better to order a protractor for the SME suggested 233.15 or order one based on the spindle to pivot number derived from the actual effective length? HMMMMMMM.

Mike