Cartridge protractor question

I use the cheap mirrored protractor with 2 null points and thought that if you lines up both points correctly you automatically had the overhang correct. But it seems I'm able to set the null points with more than one overhang distance. Any insight here? How can I know which one is right? Guessing I can't with this protractor. Note, as long as I've gotten those points right I've never had audible issues

 

If you've set the overhang and offset so that the stylus is truly aligned with the grid at both points when you go back and forth (without changing either parameter), that should only happen at one overhang. At other overhangs, one or the other point will be off tangent.

If you have a standard tonearm and table combo, it is usually easier to printout an arc protractor (if one is available), and then the overhang and offset adjustments are separated.

 

If you put the protractor over the spindle, place the needle on one of the null points and square up the cartridge with the lines on the protractor, it will have the correct overhang. Further, when you move it to the other null point the cartridge should still be squared up. Is this not what is happening? How much of a difference are we talking about?

 

With a universal protractor like this, you have to move back and forth a few times, adjusting both overhang and offset until it is aligned at both null points, unless you have another way to initially set the overhang correctly.

 

I may be mistaken, but I believe I have lined up both null points on two different overhangs, a few mm apart. It made me question if it really only worked for one overhang.

 

Make sure that you don't move the protractor between the two null point checks. You want to get the protractor's and cartridge's positions set such that the stylus will sit in the middle of of both null point cross hairs on a single arc (ie, no movement of the protractor when moving stylus from one null point to the other).

 

I don't see how this is possible with null points on same line on mirrored protractor

 

That's not how universal two-point protractors work, you have to move it for each null point. You are thinking of an arc protractor, where you first set the overhang to have stylus tip follow the arc line, then don't move it to set the offset angle at the (usually) inside null point grid, and then verify that overhang is still set correctly.

 

It will happen. You just have to find the right position for the protractor and the cartridge. A fair bit of trial and error but you'll get there.

 

I don't think you're right Davey. If that were the case, you'd never know if you had the right overhang distance. You could line up for any overhang length.

 

No, you won't get tangent at both null points if overhang is not set correctly for that alignment. A universal protractor doesn't know what the correct overhang is for your tonearm and turntable, so you have to go back and forth between null points, adjusting each time, until you get it set right.

 

The null points can not be set with more than one overhang setting in theory, but can be in practice, very true! The nuts and bolts of it, the angle of the cartridge is being changed slightly to line up the null points. (slight human error) Ideally the the overhang is set with the cartridge parallel in the headshell. There is always margin for error though, so the overhang is not your most accurate method of lining up the cartridge. Rely on your alignment grid for that.
1) overhang gets you well within the "ballpark"
2) use the protractor to fine adjust the cartridge.

Once again, we line up the cartridge by moving forward or back in the headshell, however in doing so the angle usually changes slightly... as we can not assume we have it exactly parallel every time we adjust the cartridge.

I hope this sheds some light on why the protractor lines can line up with more than one overhang adjust.. (it doesn't in theory, but in practice the cartridge angle changes slightly every time we adjust it)
Steve VK

BTW Another method of lining up the cartridge IS to angle it slightly in the headshell, but this deviates from the standard protractor alignments... and this method only for those who have a thorough understanding of arm geometry. For instance 23 degrees offset can be decreased to 20 degrees to optimize playing 7 inch 45 RPM records with zero tracking error... but not good for playing 12 inch records as the outer tracks would be way out of alignment. (advanced stuff)

 

Negative. This is absolutely impossible with a universal 2-point protractor.

 

Although there are many ways to introduce error, each turntable/tonearm combination has one correct overhang (see image below). Your protractor may be inaccurate. You can register and download a generic one here: Free Cartridge Alignment Protractors - Vinyl Engine

When using a two-point protractor you must move the protractor or turn the platter slightly when switching between the two null points. If cartridge alignment at the two points is a tiny bit off, just split the difference. Also, if using a paper protractor poke a pin hole through the null points and place an LP under the protractor to account for its thickness.

Before attempting this make sure your turntable is on a level surface and your tonearm is approximately horizontal when the stylus is resting on an LP with tracking force set to the middle of the cartridge's suggested range and anti-skate set to zero.

 

I appreciate this but just to be clear I've been aligning cartridges for years so I get the mechanics. Not sure if everyone is getting what I'm saying. I'm saying ive aligned the null points with the cart at the front of the headshell and I've also aligned it pushed back toward the rear, meaning that the protractor seems to work for multiple overhang distances, which is not what expected. I align the stylus, not the body and I try to be exact. Perhaps there is a tiny error and this explains it, but I wonder. It begs the question if this 20 dollar Gizmo can perfectly set overhang and null points, why would anyone buy one for ten times the price. Or Maybe that's a stupid question.

 

Just so this doesn't get any more confusing for folks who have not used both types or protractors, the universal or "straight line" protractors ahve a single line drawn from the spindle and both alignment points fall on that one line, since this is not an arc, like the arm travel, you have to move the protractor after looking at one point to view and adjust the other point. Going back and forth between the two until it is set. The arc protractors have two points as well but they are along the arc, so that the horizontal alignment are not in a straight line from the spindle, rather offset to the degree that they fall on the arc. This arc should be set to the correct overhang for the arm in use. On this arc, you can align one and the other should also be aligned, but you can still go back and forth and make fine adjustments if needed to be sure.
-Bill

 

Ok, I get it now and that's weird. Maybe try a different protractor? I use a Dennesen and what you're describing can't happen with it.

 

All this confusion is really why I don't like universal protractors. I prefer the arc protractor as generated for one's specific turntable and arm specs. Better than that, a simple overhang gauge is the way to go IMHO if one is available for your turntable.

 

thats where im headed

 

If you know the tonearm mounting distance of your setup, or can measure it accurately (btw, that's a very nice turntable in your profile), you can print out an arc protractor that makes it very simple to set overhang and offset for your desired alignment.

 

Doesn't the Michell Tecnoarm use the Rega geometry? Maybe you use the Rega arc protractor on Vinyl Engine. IME, these paper arc protractors are just a bit more accurate than the Dennison style.

 

Too many people are making this way too complicated.
The different overhang measurements are NOT the fault of the protractor.
As I mentioned above, the fault is human error.

When you move your cartridge back in the headshell, and line up to the null points, you have changed the offset angle (decreased it) If you observe more closely, you will see how this is 100% true. (that your cartridge will be slightly angled in the headshell)

In a textbook alignment as per protractor, the cartridge should be parallel in the headshell (if you want the overhang measurement to be right also)

When lining up your cartridge to the null points, when adjusting your cartridge forward or back, make sure the cartridge is parallel in the headshell , not angled slightly. (this is where human error enters) Your overhang will then, measure correctly, or will be very, very close. When lining to the protractor, the overhang does not need to be an exact science (this may seem crazy but this is simple geometry.. the offset should be correct if the null points are correct, in theory but often is not in practice because of human error).

Advice to avoid frustration, rely on your null points, be sure the cartridge remains parallel in the headshell when making your adjustments. Your tracking and sound will be amazing!

rock on,
Steve VK

My advice is based on many years of professional turntable refurbish and setup, (tech at our local hifi shops back in the 80's) a lifetime musician (first and foremost) and electronics tech at IBM and other computer manufacturers,

 

Additionally, always do check the overhang to verify you did things right. If the overhang is off by half a millimeter (or bit more) no problem, your alignment is good. The arc of the arm will be sufficient to track the critical inner groove very nicely. There is little to no additional benefit by trying to get the null points and overhang right on, spending hours to do so. The null points are the more critical adjustment.

If the overhang is off by a few mm, realign the cartridge. You have changed the offset.. the cartridge isn't parallel to the headshell.

 

Sure, that's usually the case, but different alignments will require the cartridge to not be parallel in the headshell. Not everyone wants to use the same alignment the manufacturer chose (there are at least three alignments in popular usage, based mainly on the minimum inner radius you normally play). That's one of the reasons it's fully adjustable (on most tonearms), and obviously, also one of the problems with playing vinyl. Look at the modern SME tonearm, the headshell is straight for mechanical design reasons, and the cartridge angle is set to whatever it needs to be.

 

Now this makes sense to me, that the multiple overhangs result from multiple offset angles. Thanks for insight!