How critical is alignment error??

Thanks Tom. I double checked my measurements and checked V-E as well. I can't move the cartridge back far enough in the head shell to achieve optimum geometry. It's back to the tech for me. I'll take Audiofeil's advice and take some pictures.

The real problem is the hassles of packing and shipping. I may take another direction and try to make the fix myself. If I do, I'll report back and let everyone know how I made out.

Thanks to everyone else for the great advice!

Bifwynne; the cartridge (and thus stylus) can be rotated slightly in a slotted headshell so that they are aligned to both null points of a protractor. That's IF the effective length (pivot-to-spindle plus overhang) is within the range needed for alignment. What you have is the possibility that the tonearm headshell slots will not allow the cartridge to be set back far enough so that the stylus is within the range of a typical alignment geometry.

If the tonearm is indeed mounted 5.0 mm too close to the spindle (217.0 mm instead of 222.0 mm) then you have to set the cartridge back in the headshell roughly the same amount.

Refering to my post above, with the tonearm mounted 217.0 mm from the spindle, you want an effective length of 234.7 mm (217.0 mm + 17.7 mm) to align to Lofgren A/Baerwald. Notice that the overhang of 17.7 mm is close to the 17.3 mm overhang needed for the 222.0 mm pivot-to-spindle distance. So basically you need to have the sylus in about the same place either way. And the offset angle is also close; 23.0 degrees vs 23.5 degrees.

The problem you've encountered is how to get the stylus back to a +/- 17.7 mm overhang. If the headshell slots don't allow the cartridge to move back far enough it won't matter how much you rotate the cartridge; it won't fit a typical alignment geometry. You need to either move the tonearm back away from the spindle or else lengthen the headshell slots so the cartridge can move back far enough. I'm not suggesting either one but instead agree with the other recommendations to talk with the tonearm installer.

If you want to see what null points you currently have with the cartridge all the way back in the slots, print out a copy of the Chpratz protractor from VinylEngine (linked below) and see which null points the cartridge lines up with.

VinylEngine protractor downloads

Regards,
Tom

Thanks guys for the advice and tips. I will recheck the S-P distance again and work the numbers on the Vinyl Engine. Assuming I can adjust the cartridge in the head shell to achieve the correct effective length, how do I adjust the offset angle.

However, I'm still confused. As I mentiond above, I have an aluminum Dennesen protractor which automatically tells you what the effective length and offset angle should be once you adjust the device by measuring the actual S-P distance. As I also mentioned, I need to shorten the effective length by about 3-4 mm, but the headshell won't take the adjustment.

Just "thinking outloud" here, I could work the problem backwards. That is, if I know the effective length and S-P distance, then the only other variable is the offset angle. So, as I asked above, how do I adjust the offset angle??? Does V-E have a compass??

Dear Bifwynne: The other thing you can make is to change the effective tonearm length. Due that you know the precise/accurate S-P distance then your " new " set up patameters will be for overhang: 17.665 mm with an offset angle: 23.46°. This is using Löfgren A ( IEC ) but you can use the same Löfgren A with DIN standard and then the parameters will be for overhang: 16.68mm with an offset angle: 22.95°.

With both set up you could have a good set up. Use the one that permit your tonearm headshell slots.
If you can't make either set up then you have to re-drill that arm mount base to the right position.

Regards and enjoy the music,
Raul.

Tom,

Well done. I am being lazy (actually playing w. my little one). But... depending on the headshell slots lengths maybe something can be done. I need to do some plug ins to the Comparator.

You can approximate unknown or non-standard parameters by using a separate alignment calculator to come up with the unknown parameters.

For example, if we assume that the design geometry of the original tonearm was for Lofgren A/Baerwald then the parameters are as follows...
Effective length: 232.8mm
Overhang: 17.8mm
Pivot-to-spindle: 215.0mm
Offset angle: 23.7 degrees

And the design geometry of the new tonearm is as follows...
Effective length: 239.3mm
Overhang: 17.3mm
Pivot-to-spindle: 222.0mm
Offset angle: 23.0 degrees

Then the current setup (based on Bifwynne's estimate of pivot-to-spindle distance) should have a geometry as follows...
Effective length: 234.7mm
Overhange: 17.7mm
Pivot-to-spindle: 217.0mm
Offset angle: 23.5 degrees

However, Bifwynne states that the overhang is about 3-5mm too long so, using the lower value, the overhang is now 20.7mm and effective length becomes 237.7mm. (What's missing is which alignment protractor geometry is being used to estimate incorrect overhang.) Compared to the "correct" alignment parameters the current setup doesn't look very promising, as shown in the chart and graph from VinylEngine

VinylEngine Tonearm Alignment Comparator

Regards,
Tom

Like I said, "without the ability to correct the figures for the error." Where is that option provided, on the Vinyl Engine website(the only one you mentioned)? Maybe I missed it.

Rodman,

Yes but he can plug in the deviation and check the change in distortion. He can even print a new protractor to compensate. A lot can be done. Remember effective length is a design element with a nominal figure. Take a look at an SME where there is no nominal length but an exact length but yet pivot to spindle distance can be changed and that is all. The headshell if fixed for all parameters for the most part. If you are lucky a poor setting can end up being the correct setting. Just like some arms can be setup w. Lofgren A or B.

Plugging his overhang figure into a formula will be worthless at this point, without the ability to correct the figures for the error in his spindle to tonearm pivot distance. VE's formulas(like ANY given alignment protractor) assume a correct spindle to pivot distance for the tonearm's length. The existing error throws off the whole geometry of the process(and geometry is EVERYTHING, regarding tonearm/cartridge alignment).

The error might not even be for the worse. Go to the vinyl engine website & enter the overhanf #s etc & calculate the distortion. I know I will get it on this site but HTA is not as important as VTA & Azimuth unless grossly off. But use VE calculations to confirm. The distortion figures should be easy to come up with. Remeber many arms might natively have higher distortion than some longer arms. One caveat 222 is a fairly short effective length. But sometimes longer can be better.

That error is not subtle.

I agree. And if you sent him instructions showing how to do the work, its hard to understand why he did not. I agree w Elizabeth that the place to start is w an inquiry, not an agruement (it may end up there, but you gotta try to resolve it in a friendly manner). Good luck.

How important? In a word, "VERY"! Then again, it all depends on how important it is to you(can you hear the difference, or will you obsess about it regardless?). Personally; It would bother me. This recent article will give you some excellent insights: (http://www.stereophile.com/features/arc_angles_optimizing_tonearm_geometry/)

Elizabeth: Any comments about the question raised in my original post, i.e., how much distortion will the overhang error introduce in the playback?

BTW, I did not bargain shop for the work, and yes, it was stipulated that he was to do the work in a "workmanlike" manner, which means, the right way. As far as drilling holes, I found instructions on the web which explained how to install the arm in question on my TT and sent it to him. And yes, the installation instructions contemplated drilling out part of the undercarriage to make room for the larger arm.

That error is not subtle. It is in analog terms not in the wrong street of town, it is like being on the other side of the world.

Send the "tech" pictures with measurements and ask for your money back.

Then find somebody who knows how to do the work properly.