Moerch arm questions

Presumably, as already I check the sight line to the pivot when the cartridge is just above the alignment grid, I don't need to worry too much about this difference in pivot point?

 

I think Jack means this:

 

Hmmm. How does it work that's its so accurate? - from what I could see it still relies on you eyeballing the cantilever down a line. Not popping, genuinely interested.

 

Well, something like the polaris asks you to align and measure pivot to spindle by eye - effectively to guess - and then make measurements that must be accurate to less than a mm. The vinyl solution's approach is to take multiple measurements of each parameter and average them out excluding any that are obviously, wildly different, but you still have to guess that initial P to S distance, and ensuring everything is properly aligned is a pain and not especially precise.
The Feickert / Clearaudio approach ensures that the initial measurement/alignment is very accurate and relatively easy to do. After doing this, I used the vinyl solution to apply curves I had made using its spreadsheet. Many of the calculators available on the net allow you to do the same thing (if I was spending money now, it would be on the Feickert + a free calculator)
Of course a morch wobbles around a bit when its on the record, so all this accuracy is rather moot - but at least it is as accurate as I can reasonably make it.
The Feickert isn't mine BTW. I'll be back to using lengths of string and bits of tape next time...

 

Well, except that a normal 2 point protractor, doesn't involve the dubious alignment of arrows either. Two grids at the correct angle for a given alignment and one hole, no arrows - no room for error.

That Polaris one, needs the arrow because because they used one grid and two holes - which adds a needless complication, and takes away a degree of accuracy.

I've seen various attempts at improving on a normal two point protractor and all seem to make it more difficult to use without making it any more accurate.

It is true that a two point protractor is only ever going to be able to provide alignment for whatever alignment it was printed to use. If you want to set it for your own null points then it won't work. That said, the Chpratz protractor (also one of the downloadables from VE), does allow you to do this, as well as showing you the percentage tracking error between and either side of your chosen null points. Again it does it in such a way that there is no room for the errors introduced lining arrowsup with the pivot.

EDIT: actually, thinking about the Polaris protractor. I'm not entirely sure what the arrow is for, maybe there is something I haven't considered - happy to be enlightened.

 

I think Joel kind of answered this. It's to do with pivot-spindle distance. If the arrow is pointing exactly at the pivot point and either hole A or C is over the spindle then there is a right angled triangle with A (or C), the pivot and the intersection of the line A-C and the arrow line as it's corners. As A and C are equidistant from the arrow line the two triangles (A at spindle or C at spindle) will be the same - assuming the arrow is pointing at exactly the same point in both cases! It doesn't measure pivot-spindle as such but it includes it the process.

At least that's the way I understand it.

 

Hmmm? Okay ... it still begs the question as to what it adds in terms of accuracy (not a lot it would seem) and what it takes away (accuracy presumably as it requires you to align the arrow).

A standard one hole, two grid protractor requires no alignment with the pivot and will provide accurate alignment, and correct overhang, without recourse to aligning any arrows (and subsequent room for error). I should add that this is assuming the spindle to pivot distance is correct(ish), I say ish, because most arms allow for enough wiggle room in the headshell slots to achieve the right result even if spindle to pivot is out by a mm or so.

Its simple, its effective and its as accurate as any other method. All other methods I've seen are either less simple or less accurate or both. Put simply the cantilever will only align on both grids if alignment and overhang are correct.

 

in my (very, very) limited experience, once the pivot spindle distance is right everything else is a lot easier

but

measuring the pivot spindle distance is tricky, unless you have something appropriate for the job and/or (with a spacedeck) you don't mind taking the platter off a few times; and of course you need to know what the distance is supposed to be in the first place!

the polaris sort of gets you there without throwing up too many further questions or requiring extra bits of kit, but, to quote Tom slightly out of context, it will get you to the right haystack but won't necessarily help you find the needle

I get the feeling he is much happier setting absolutely everything up by ear

 

Not just a lot easier, if it isn't reasonably close its impossible.

If the spindle to pivot distance is out by more than you have wiggle room in the headshell, you are on a hiding to nothing, you won't ever get it to align, no matter what method you use - you are in the wrong field let alone haystack. Otherwise a mm or so either way isn't going to cause you a whole lot of grief (hence why I said ish).

The Polaris won't tell you whether your spindle to pivot distance is correct any more than a two point protractor will. Just like a two point protractor, it will just tell you that you are close enough given the allowable wiggle room ... or not close enough.

To be honest whenever I've done the initial spindle to pivot measurement on a space deck, I've just eyeballed it with a ruler platter and arm off. I've yet to find myself in a situation where alignment couldn't be achieved, so it must be close enough.

Now if after aligning, the cartridge is a bit skew in the headshell it just means the arm designer set the headshell offset with a diferent alignment in mind. Which alignment to choose is whole nother debate, and who is to say your chosen alignment is righter or wronger than the guy who chose the offset for the arm. It just looks prettier if it sits dead in straight

 

I do understand what you are saying but: changing the spindle pivot distance is different to moving the cart backwards/forwards/skewing it in the headshell. The movement is in a different direction (ok, except when the headshell offset allows it to be parallel to the spindle pivot line) and the pivot is a fixed point whereas the cart is always on the move relative to the record. Not sure what the implications of that are; but they are different things.


just another spacedeck point while we are here:

are the fixed foot and the front foot actually in the same position relative to the circumference of the platter? ie if the base didn't have the cut off bit at the front where the label is would both feet look like they were equally under the base?

 

I suspect the implications aren't anything to lose sleep over EDIT: thinking about it assuming we get alignment 1mm too short spindle to pivot will cause fractionally (and it really will be miniscule) more tracking error either side of the null points. 1mm too long and you will get fractionally less. The difference is not going to be noticeable. But if you are going to err, erring on the slightly too long might be the thing.

I don't know as mine has two arms, so effectively only the front foot is fixed. I'd guess that if I only had the one armpod it would be, so would the fixing point for the single armpod as the back left foot bolts to the same hole as the second armpod and looks to be in the same place as the hole for the first one. Don't fancy tipping it upside down to look though.

 

As I use an RB250 I tried using a Rega specific protractor. This is designed for Rega decks so the pivot spindle should be spot on. Result with the space as I had it was the outside point was fine but the inside point was way off. Nudge the pivot spindle a mm or so shorter and it was spot on all the way

Was wondering about the pivot/armpod bolt/spindle all in a line thing. If the other two feet are as suggested then when the pivot is in line you would get a nice isosceles triangle.

 

You're spot on! I think I even lost mine! Well done for finding it!!


jack

 

My mammoth run of summer house building is in remission and I have had a chance to finish setting it all up....



Sounds very nice indeed. Many thanks for everyones help, and apologies for hijacking the thread to a large extent.

Chris.

 

and very nice it looks too Chris... is ith pic though or is your azimuth off

 

Ha-di flippin' ha.

Its the photo, luckily - azimuth is hopefully spot on (I can't hear an imbalance and it is dead straight in the reflection), as is arm height, even though the picture makes it look like its high at the back.

 

I think the magnitude of error is greater than a mm if you do not know the exact P-S distance and if your gauge is not aligned exactly with the pivot (see the arrow on the polaris...). This is a variable that the feickert system takes care of.
Whatever system - Bayerwald, Stevenson, or something else, you use is up to you or should be.
No system is perfect. nor I suspect can it be, but the idea is to reduce those variables that can be reduced. For this, Feickert proved useful to us (myself and the designer of the cartridge I use in the case of the photos above...)

 

Joel, a two point protractor doesn't have an arrow, because it doesn't reference the P-S distance and doesn't need the P-S distance to be perfect for alignment to be absolutely dead on (its a given that if its way out, you won't ever get it aligned whatever method used). That's why its universal for all arm lengths, and is why its so accurate even if P-S is a bit out or not.

If you are saying the Feickert will ensure you have the P-S distance spot on, then sure but that isn't what an alignment protractor does - but that's because a 2 point protractor is for getting alignment and overhang right independently of P-S distance. P-S doesn't need to be fractions of a mil perfect to chieve perfect alignment. It only needs to be perfect if you use an alignment method which requires it to be, which the two point method doesn't.

If it is aligned on both grids, then alignment and overhang are necessarily correct with zero error.

Edit: Here is a two point protractor (Stevenson in this case) ... note the lack of arrows:

 

What I should have made clearer perhaps is that I was looking for an optimised solution for my TT. Using a two-point protractor like the one above and you are stuck to one effective P-S distance - because that is that Stevenson assumes. With Stevenson, unless you own a Rega deck, this will possibly mean jamming your cart far back on the headshell. Not even be possible with my cart/arm.
Of course you could move the arm to the appropriate Stevenson mounting length. This is a task made much easier using something like the Feickert...
I think there are no perfect solutions. Vinyl is an imperfect medium, and yet it works. The Feickert (or similar - someone good at these things could make their own easily enough I think) makes life a little easier.