STP distance. Is it critical ?

Is the Spindle To Pivot distance critical with a slotted headshell.

I am talking a difference of +/- 1 or 2 mm.

For sake of discussion, i have a Graham Phantom II and a Mint LP.
Will i still be able to track the entire arc if the stp distance is off a bit?

The specs are:
STP distance is 217.5mm
Effective length is 235mm
This necessarily depends on (i) the stylus-to-mounting holes dimension of the cartridge and (ii) the length of the headshell slots.

As to whether any particular cartridge will be able to track the arc, the surest way to know is to try. It only takes a couple of seconds.

Of course if you don't have the cartridge yet you may be in for some guesswork. Stylus-to-mounting hole dimension is not commonly quoted so you'd have to ask owners to measure for you, then compare with cartridges on hand that you know can track the arc.
I am trying to learn about this since I need to mount a tonearm. Altough the template is good, I suspect I could be off a millimeter or two when done drilling the hole and mounting it.

Reading Doug's post, would it be correct to state that if the headshell slots are at least 2 mm long, then this would compensate for a 1-2mm error in pivot to spindle mounting distance?
This might help:

You can see in numbers what difference there is.

I think the effective length of the arm will change if it is mounted somewhere other than its designed location. I might be wrong, but it makes sense that the arm would swing through a slightly different arc. The manufacturer's template would not line up quite right.
This might help:
The link did not come through correctly.

Here's another attempt:
Yes, it is critical. When you want to have the specs from the manufacturer to get the best result of this calculated Arm. Some Arms work also with differences (Loefgren and Baerwald are not the only valid datas), but then you need a different alignment System. Otherwise you will ruin the grooves sooner or later. Analog reproduction is precision.
Dear Smoffat: Everything is almost critical in cartridge/tonearm set up depending what you are looking for.

In a cartridge/tonearm set up you can't change the effective length: the distance from stylus to tonearm pivot center.

All the geometry calculations/equations were made with this effective length parameter with a fixed/permanent value and inner/outer most grooves distances.

Baerwald, Löfgren or Stevenson set up calculations take all those three values to obtain mainly : overhang, offset angle and STP distance.

You can find through the net all these geometry calculators where the only parameter that you need give to the " Calculator " is tonearm effective length to have all the set up parameters.

Even you can choose between DIN or IEC standards or even you can make tyny changes on the inner/outer most distance values.

In all cases you will have all the parameters need it to cartridge/tonearm set up and you can use any one of them with your Phantom and decide which works fine for you or wich one you prefer.

With any of these kind of geometry set up calculations the tonearm can be placed anywhere if you respect the effective length at null points.
Yes 1.0mm-2.0mm makes a difference and not for the better.

As Syntax point out: " Analog reproduction is precision. "

Regards and enjoy the music,
Smoffat, making a couple of assumptions about the tone arm you can see what the results might be by using the calculators available at VinylEngine. Let's assume that to set up for Lofgren's A (Baerwald) alignment with an effective length of 235mm and spindle-to-pivot distance of 217.5mm that the corresponding overhang would be 17.5mm with an offset angle of about 23.4 degrees. (If you know the actual offset angle/overhang you can get more accurate results.)

The calculator will indicate the effect of moving the tone arm +/- 1mm of the specified STP while maintaining the specified offset angle and effective length of the tone arm. (Overhang is changed by +/- 1mm to accomodate change in STP and keeping effective length constant.) The graphs display the resulting tracking distortion.

If your STP distance is 1mm closer at 216.5mm ("Custom"):

If your STP distance is 1mm farther at 218.5mm ("Custom"):

However, you may be able to accomodate the needed change in offset angle by rotating the cartridge within the headshell slots. For example, if you change effective length by 1mm to 234mm (STP is 1mm too close), you may be able to achieve Lofgren's A (Baerwald) alignment by rotating the cartridge so the offset angle is now 23.5 degrees. The alignment will be very close, depicted as "Original"/"manufacturer":

Thank You all for the info you have provided. To make it simple, i will ensure that the STP distance is dead on BEFORE i attempt to align the cartridge (A90) with the Mint LP.
Thanks again.
Dear Smoffat: According to Baerwald ( IEC ) calculator for an effective length of: 235mm the precise STP distance is: 217.36mm and with DIN standard: 218.41.

The differences in DIN against IEC is not only with the STP value but there are differences too in the offset angle and obviously overhang.

Regards and enjoy the music,
Forgive my ignorance Raul but, what is IEC and DIN and the difference between both.
Which should i use.
My tonearm is Graham Phantom II and Ortofon A90.

Dear Smoffat: Are standards from International Enginnering and from Germany ( Deutch ) inner/outer most distance groove that are two values necessary for the calculations.

Your Phantom manufacturer specs seems Baerwald IEC and I assume that your Mint LP protractor too. So just follow it.

Each different set up geometry calculations made differences in the percieved system sounds. So, if we have the tools, we can test either equations with either IEC/DIN standards and through listening decide which one match our priorities.

Here you can download Baerwald/Löfgren B calculators:

you only need to make click with your mouse in: Donload Now ( at the bottom of the page ).

Baerwald is Löfgren A in that sheet. The original values in the calculator inputs are IEC standard, you can change to DIN standard changing the input inner most value: 60.325mm by the DIN innermost value: 57.5mm

If you only want to use the calculators with IEC standard then the only value that you have to introduce is the tonearm effective length at the calculator input, then you make click in the CALCULATOR word ( in white at the center. ) and appear at the right ( green color side ) the output parameters that you need to the set up.

It is more easy to use that my explanation.

regards and enjoy the music,
I think this is how it works....

Consider the arc of the stylus as it swings across the record surface. The proper set-up establishes two null points where the cantilever is on exact tangent to the groove, the inner and outer grooves have a small out-of-tangent angle.

Moving the pivot point of the same arm away from the platter center changes the position of the arc across the record surface. The two null points are moved closer together and the tracking angle at the inner and outer grooves is greater. Sound quality suffers at the outer grooves, but the tracking between the two null points is a little better.

Moving the pivot point of the same arm close to the platter spindle moves the null points farther apart resulting in a greater tracking angle error across the middle of the record, but coming closer to tangent on the inner and outer grooves.

In both cases of "improper" set-up, the worst-case tracking error is greater than if the arm/cart is set-up as designed. The differences in cartridge alignment points is based on the location of null points, and the location and degree of tracking errors.
Hi, Bpoletti: good description, and I appreciate that you put 'improper' in quotes. But worst case tracking error is relative. It's a matter of choice as to where along the path of the stylus that the listener hears the faint trace of distortion. The debate on which alignment null points are "optimal" will continue as long as people use pivoted tone arms.

Dear Bpolleti: You can make any " move/movement " you want with a pivot tonearm and always will have worst results that if you respect the different geometry set up equations where what you can change are the most outer/inner groove distances, the tonearm effective length must be the same.

If you move the pivot to spindle distance at random you have almost " nothing " but higher distortions..

A pivot tonearm always was and is designed with a precise effective lenght in mind/target not pivot to spindle distance, at least I don't know any pivot tonearm designer that his main tonearm target was the pivot to TT spindle distance but I can be wrong.

regards and enjoy the music,
Dear Raul, This is a kind of student-teacher situation; me
being the student asking the teacher if he is not'forgeting something'. We assume that all designers start with pivot-spindle (exact)distance. For the eff. lenght however they must assume éxact position of the stylus. As J. Carr stated there is no standard position or norm for the stylus. That is why those 'slots' in the headshell are needed. To compensate the (lack) of the standard.Ie to get the stylus where the designer ímagined its position.

Raul, I'm not sure we're in complete agreement on all points.

I do agree that respecting the designer's geometry will result in the tracking they had in mind when creating a given arm. Most of the time, this is the geometry that will yield the lowest "worst case" tracking error.

The effective length, cartridge mounting angle and spindle-to-pivot distance are closely related. Designers must consider all of these variables for an arm. Changing the value of one changes the value of the others FOR A GIVEN GEOMETRY. (Not shouting, just emphasizing the point.) It's all about math / geometry.

For any given arm, when the cartridge mounting angle is fixed as designed and the effective length of the arm is as designed (this includes stylus overhang), there will be one position of spindle-to pivot length that will work for the designer's lowest "worst case" tracking error and null point across the swing of the stylus over the record surface. (sorry for the long sentence) Changing one parameter of the three will change the geometry. There will be different null points on the arc, the "worst case" tracking error may be higher.

To illustrate this, let's look at different arms from the same manufacturer. A VPI JMW-series 9" arm will have a designer's fixed effective length, spindle-to-pivot distance and cartridge mounting angle. Changing to a 12" wand changes EVERYTHING (for a given geometry). The designer's spindle-to-pivot distance and effective length increases, the cartridge mounting angle changes (decreases). The arc shallows across the record resulting in smaller "worst case" tracking errors FOR THE SAME GEOMETRY (fixed null points). The spindle-to-pivot distance is critical to the success of the geometry.

It is possible for a user to change the effective length of an arm by increasing the spindle-to-pivot distance and increasing both the overhang and slightly reducing the cartridge mounting angle. These variables are all closely related for a given geometry. Careful computation and positioning in this scenario could result in a smaller "worst case" tracking error (for a given geometry).

It's not difficult, it's not subjective, it's math (geometry).


Dear Nandric: I already email you an example of equations used to find out tonearm design geometry parameters where you can see/read that the input/variables for those equations are these " numbers ": effective length and inner-most and outer-most values.

The STP distance comes by: effective length minus overhang.

IMHO a tonearm designer define first if he want a 9" or 10" or 12" effective length tonearm ( he does not cares about where the stylus in the cartridge comes, it does not matters: the cartridge designers has almost no standards about. Every one is almost different where the stylus comes in the cartridge. ) and not the STP figure that is only a result after knowing the other parameters through the equations, in specific the overhang.
At least this is the way how we start our self tonearm design.

Maybe there are other tonearm designers that goes through STP parameter but I doubt. Like I posted maybe I can be wrong but this is MHO.

Regards and enjoy the music,
Dear Bill: Now that I read both of your posts I think we are talking almost the same.

All those different set of equations were made to optimize/put at minimum the tracking error somewhere but to bring at minimum the tracking error means that we have to choose in what part of the LP recorded surface grooves we want to do it because we can't do it all over the recording LP surface.
So always is a trade-off choice.

The interesting for me in this whole subject is that in almost any pivot tonearm we can change those equations parameters and with the same cartridge see what happen and what works better in the audio system.

Now, IMHO for we can heard/hear differences in quality performance due to this geometry changes it is a must that in each time we test it the cartridge/tonearm set up were made almost perfect.
The analog medium is so imperfect that in this subject we have to be " perfect " to achieve a valued information.

Regards and enjoy the music,
Dear Bill, Not so sure if the math. is so sure (see fundations). Enyway the math is not subjective. But we all
are trying to get the stylus on those null points. But if
we use,say,SME V with holes and not slots how are we (pre)
supposed to get there without changing the SPD? Ie I assume that eff.lenght is pivot- stylus distance.

Hi Raul,

I think the point you were trying to make earlier that a designer didn't need to consider the spindle-to-pivot distance was what caught my eye. If you intended to mean otherwise, then we are in agreement. All pivoted arms have some degree of tracking error. It's just the nature of the beast.

Wouldn't it be nice if all tonearms were linear tracking to match the cutting process?


That's a good point regarding the SME V.

It would be nice to get some insight on the geometry model from the SME designer(s).

Dear Bill, J. Carr proposed 'éasy way' out for the SME V:
recalculate the geometry (thread reg. SME V?).
My (other) question. According to SAEC engeneers the balance in all 3 dimensions across the radius is of much
importance. Can you explain this claim?


Dear Nandric,

I agree with Jonathan (who am I to disagree with such an expert!?).

The way I read the SAEC engineer statement emphasizes what is being discussed in the thread. Changing one of the three "dimensions" changes the other two for a given geometry. If the STP increases, so does the effective length, the cartridge offset angle shallows. Each geometry has a different ratio, but the same principles apply.

If one of the dimensions change without changing the other two, then the geometry is different.

Take a glance at this table to see how the dimensions are interrelated. This table is for a single geometry / location of null points. Other geometries will have different ratios.

BTW, the dimensions illustrated in this table vary a little from the ones provided my Micro Seiki for the MA-505 standard length arm (237mm, 222mm, 21 degrees 50 minutes) which uses a different geometry.


Dear Nandric: ++++ " But we all
are trying to get the stylus on those null points. But if
we use,say,SME V with holes and ...." +++++

I can't understand what you exactly men with the V.

SME V was designed with Baerwald geometry, its null point are right " there " .

If your tonearm is mounted with the precise STP distance then you have not any single problem to achieve the SME null point.

Please let me know what I'm missing here.

regards and enjoy the music,

The issue with the SME V is that the holes for cartridge mounting do not allow for any other cartridge position or adjustment of the cartridge in the headshell. This would be OK if all cartridges used the same "mounting hole to stylus distance." Bit there is no standard value for the position of the stylus relative to the mounting holes in the cartridge. Therefore, as the position of the stylus relative to the mounting holes changes, then so does the effective length of the arm. Since the effective length changes, so does the STP distance. Increase the effective length and the STP, and the cartridge offset angle must decrease.

So the geometry of the SME arm changes most every time there is a change of cartridge. In some cases, it seems that the cartridge offset angle will not be a good match the effective length / STP.

Even though we're talking about VERY MINUTE differences, I wonder if that might be one of the reasons that the SME V arm doesn't seem to perform as well for some users.

Dear Raul, If I understand the design of SME V then the designers assumed the exact position of the stylus in all
carts. Otherwise thy would make slots in the headshell.
The actual carts are some kind of 'movenig targets'in this
respect. So to get the right eff. lenght or those null points one must 'slide' the arm and consequently change the SPD. If I understand J. Carr correctly one should recalculate the geometry for the 'deviant carts'. BTW in some other models SME changed the headshell.

Changing one of the three "dimensions" changes the other two for a given geometry. If the STP increases, so does the effective length, the cartridge offset angle shallows.

This only makes sense...

As P-to-S increases, effective length must increase (logically). Also, as P-to-S increases, overhang decreases and cartridge offset angle shallows.

Taken to the extreme (as P-to-S goes to infinity), the overhang goes to 0 (as P-to-S and effective length becomes equal) and offset angle goes to 0 as well. This is what a linear tracking arm attempts to mimic.

No thanks necessary for me pointing out the obvious. I'm here to help.
There is a range of tracking errors that sound similar if not identical. (I would admit that with certain vinyl setups the differences may be more noticeable.) To provide some perspective: Given the gamut of alignments, including Lofgren A (Baerwald), Lofgren B, and Stevenson plus the myriad of "custom" geometries and alignments, each considered optimal to portions of the vinyl audiophile community, there is more than one "optimal" alignment geometry.

I use a SME tone arm and the differences in tracking error from one cartridge to the next are so slight that I do not worry about it. Some cartridges result in less distortion across the mid-section of the groove while others have less distortion at the beginning and end of the groove. I've learned to accept the range of alignments and would be hard pressed to detect the differences with many if not most records anyway.

So when we start to nit pick over the merits or disadvantages of specific modulated groove radii, null point radii, and nominal effective lengths, I believe we're teetering on the edge of being bumptious if not dilusional.

I would agree that certain combinations of cartridge and tone arm may not play nicely with certain alignments and that there are some cartridges with atypical mounting hole parameters that will not work well with fixed headshell offset angles, but within the range of typical cartridge and tone arm geometries there is a range of alignments that play and sound just fine.

Or not. :-)

Dear Tketcham, I quoted Carr in my post from memory but the
thread is:'Allignment tool for SME V + Shelter'. To prevent any suggestion of 'belittling' the SME V I need to
add that all the owners , Carr included, are very fond about their tonearm. However even Carr admited that because of those holes in the headshell one needs to adjust the geometry to accommodate 'some carts'.As he put
it:'Simply recalculate and readjust the overhang,likewise
for the offset angle (the ...difference between screwhole diameter and srew diameter should be enough to accomodate the majority of carts)'. Well simplicity as well as complexity are persons-relative so I bought Triplanar because of my math.
While this thread is already complex I don't believe that
adding 'the range of tracking errors that sound similar'
will help to simplifid the issues.

Hi, Nandric, I wasn't addressing anyone in this thread specifically, but I do think that talking about a range of tracking errors will help to clarify (and subsequently simplify) the issue of cartridge alignment. The endless debate over the "best" alignment geometry just confuses and frustrates people trying to align to the "best" geometry and their particular tone arm and cartridge doesn't allow it.

The problem is that many (if not most) tone arm and turntable manufacturers aren't forthright about which alignment geometry they used in the design and the owner is left to find the information themselves or figure it out by trial and error. When the owner tries to learn what they need to know they run into a sea of possibilities with often conflicting recommendations. Manufacturers should be more forthright about the geometry of their products and even provide recommendations and alternatives for alignment.

Because there is no standard for cartridge mounting holes or tone arm geometry I think the audiophile community should stop debating on the best alignment and start helping to explain the range of alignment possibilities for each combination of tone arm and cartridge. Web sites like Vinyl Engine have some very useful pages of information and graphing capabilities but even then it can be intimidating to try and figure out what you need to know and how to use that information.

Lastly, I think alignment template designers and manufacturers could be more accomodating of variable alignment geometries and include the ability to align for a range of geometries. There are excellent printable arc templates (protractors) that accomodate variable tone arm and cartridge parameters and there are a few excellent alignment protractors that can be purchased retail that have variable effective length/offset angle capabilities. But most alignment protractors/templates are designed for a specific alignment, such as Lofgren's A (Baerwald), with specific null point radii that may not be easily attained because of cartridge mounting hole parameters or headshell design.

SME's sliding base and alignment template is one of the most simple and easy to use combinations around. Even then, audiophiles complicate things by insisting that specific null points be attained, e.g., 66.0mm and 120.9mm, when a particular cartridge design may not easily allow for that alignment. The resulting SME alignment may end up instead at null points of 63.9mm and 119.1mm and be a perfectly fine (if not superior) alignment. But because it isn't using the so-called "best" null points the owner believes the SME alignment is inferior and not acceptable.

Custom protractor templates are available but they can be limiting in which cartridge designs can used with the tone arm and are of no use if the tone arm/turntable is sold. By offering alignment protractors that provide for a range of alignment null points depending on the resulting effective length, pivot-to-spindle distance, and inherent offset angle of each tone arm and cartridge combination, the cartridge alignment process would be much easier and understandable for the owner.

Best regards, Tom
Dear Tom, For those that are not blessed with mathematical talents: order the Mint tractor. That is what I deed.
Regarding your 'similarity argument' I am sorry but I was not able to resist the 'çhalenge'. In Holland we have the
saying:'from the rain in the drip'. To put it paradoxicaly
the identity relation is 'similar' to the similarity ralation. But the subject of identity is so 'easy' that nobody wants the demn thing. It is not part of logic nor mathematics or physics. So the philosopher got this subject for free . Your lucent Quine was nearly drown trying to explain this 'bathing in the same water in the same river' puzzle from some old Greek.

Hi, Nandric, your use of Quine's argument is appropriate. The process of cartridge alignment can be as complicated as we make it but what is needed is an elegant method that considers a wide range of tone arm and cartridge combinations.

From W.V. Quine's paper titled "Identity, Ostension, and Hypostasis": "Elegance can make the difference between a psychologically manageable conceptual theme and one that is too unwieldy for our poor minds to cope with effectively."

Elegance in the case of cartridge alignment would be variable geometry protractors. And: "Where this happens, elegance is simply a means to the end of a pragmatically acceptable conceptual scheme."

Best Regards and enjoy the day.

Dear Tom, I also admire Quine but your problem is,uh, similar to the war that was meant to end all wars. To my
mind this is the lanquage issue. The capability of speakers to generate from limited lanquage resources a unlimited amount of sentences and questions. And this process starts very early. Look at those 5-6 years old kids. They look like asking-machines. While we of course are crazy obout them it is a wonder that we don't get crazy from them. But they have also the capacity to remember our answers so no wonder that at certain age they
refuse to listen to us. If our analog hobby survives for,say, 20 years I am sure that even then there will be
questions about the right geometry and the best way to adjust cart/toneamrm combo.
Best regards,
Dear Tom, To defend my advise reg. the Mint tractor I need to add as follow. According to Yip from the Mint tractor the spindle diameter on diff. TT's varies from 6.4mm to 7,3mm. So your 'universal tractor' is not such a good idea.
Yip has the data of the most TT's, tonearms and carts. So every tractor that he produce is meant for a specific combo. I own two of those and am very satisfied with the result. But more important the others seems also to be very
fond about their Mint tractors.
Hi, Nandric, as to the different spindle diameters, if you're familiar with the DB Systems protractor, which uses a set of overlays to find correct alignment, a similar setup could be made that incorporates both spindle diameters found on turntable platters. This is but one design concept that could used to build a universal protractor.

I'm sure the Mint protractor is an excellent alignment device and never intended to disparage it's value. But it is limited to specific turntable/tone arm combinations and so is far from a universal protractor, which is what I'm advocating.

Best regards,