Free Protractor To Align Your Turntable Cartridge!
Well, there's no place like home.
Home is where my turntable is and everyone should have a two point protractor.
In Use: The trick is to have the cartridge
mounted so that the needle aligns perfectly on BOTH dots without moving the protractor. What you may
need to do is mount the cartridge a bit loose and slightly move
it forward or back and see how it aligns on both points. You know you have it perfect when both points are perfect without moving the protractor. It takes time and patience to get it just right, but the results are worth it!
As always, if you have any questions please feel free to
e-mail them to me. Thanks!
Click here for cartridge alignment tool
Click here to view the
two point protractor in action.
Excel Spreadsheet Versions!
Excel Spreadsheet To Make Your Own Protractor!
You'll find an Excel file at the link located below this article. It is a two page spreadsheet-one page for Löfgren "A" alignment and one page for Löfgren "B" alignment. Interestingly, from all the reading I've done recently on the subject, it seems that Professor Erik Löfgren was actually the person who developed modern tonearm alignment geometry back in 1938. Baerwald, Stevenson, and others came along later, and each published alignment geometry equations which have been shown to be identical to those published by Löfgren, and yet they included no recognition that Löfgren had already published the same equations. Baerwald even lists Löfgren's paper in his references.
At the core of Löfgren's alignments lies the weighted tracking error curve, which is essentially tracking error per unit of groove radius. This weighted curve places more emphasis on tracking error for inner grooves than for outer grooves, which is representative of the actual distortion caused by tracking error. The difference between the two alignments is that Löfgren's "A" alignment minimizes the weighted tracking error curve directly while Löfgren's "B" alignment minimizes the area underneath the squared weighted tracking error curve. In other words, Löfgren's "A" alignment minimizes peak distortion while Löfgren's "B" alignment minimizes RMS distortion. The advantage of Löfgren's "B" alignment is lower tracking distortion during more playing time at the expense of slightly higher distortion at the beginning and end of the record. Löfgren's "A" alignment minimizes and equalizes the distortion peaks at the innermost groove, in-between the null-points, and at the outermost groove.
Okay, so how does the spreadsheet work? Well, the easiest way to operate the spreadsheet is by using the Löfgren "A" or "B" calculator at the top of the spreadsheet page. The calculator has three yellow input cells and six green output cells. Inputs are effective length, innermost groove, and outermost groove. Outputs are angular offset, linear offset, stylus overhang, pivot-to-spindle mounting distance, inner null-point, and outer null-point. The default or initial input values are 228.6mm (9") for tonearm effective length and the IEC standard innermost and outermost groove radii of 60.325mm and 146.05mm, respectively. The output values change in accordance with the equations listed in the instruction area below the graph when new numbers are entered into any of the yellow input cells.
The graph is a visual representation of the columns of numbers on the left, which are a function of three specific tonearm parameters, effective length, angular offset, and stylus overhang as displayed in the tan colored cells, A3, B3, and C3. These are also spreadsheet input cells, but initially they are linked to the corresponding calculator cells, I3, O3, and Q3 so the calculator controls the entire spreadsheet. However, the tan colored cells may easily be unlinked from the calculator simply by entering numbers into them. If this is done, the calculator operates autonomously from the rest of the spreadsheet. The graph and the rest of the spreadsheet are controlled by inputs to cells A3, B3, and C3 only. One reason for unlinking the calculator might be to evaluate a tonearm's geometry by inputting effective length, angular offset, and stylus overhang directly into cells A3, B3, and C3, respectively. You'll find some interesting designs floating around out there with alignment geometry's based on something entirely different from either Löfgren "A" or "B."
For advanced spreadsheet users, the Excel "Solver" function is a very powerful tool that can be used advantageously with this spreadsheet. "Solver" lets you turn output cells into input cells through an indirect iterative mathematical process. For example, suppose you wish to evaluate Steven Rochlin's alignment tool, which has alignment null-points at approximately 70mm and 127mm. You could ask "Solver" to find new innermost and outermost groove radii that would yield Steven's alignment null-points, and you would also get a graphical representation of Steven's tracking error and distortion curves. There are many ways "Solver" can be used to enhance and expand the capabilities of complex spreadsheets.
As a word of caution, only six cells on the spreadsheet should be used for entering numbers. They are the three yellow cells, I3, J3, and K3 in the calculator at the top of each page, and the three tan cells, A3, B3, and C3, which control the graph and the rest of the spreadsheet. Please do not enter numbers into any other cells; otherwise you may destroy important equations that enable the spreadsheet to function properly. As an additional precaution, I recommend you archive a copy of the spreadsheet and always use a different working copy, just in case something goes wrong and you want to return to the original. Other than that, have fun calculating.