Linear Tracking versus Pivoted Tonearms: A discussion

[J.R. Boisclair]

thekong, I simply use the same protractor moving the SME sled base forward to account for a slightly shortened effective length or backward to account for a slightly longer effective length. This changes the pivot to spindle distance. I still get alignment at the two null points with headshell edges (or my jig edges) parallel to the lines on the protractor.

This is geometrically impossible. It may appear this way because your magnifying power is insufficient to resolve it, but it is a geometric impossibility.

This suggests that zenith is correct at the two null points.

“Zenith” is NOT cantilever alignment. Zenith error correction and cantilever tangency are two very different and competing objectives. See here:
Sound Bite #36: Tracking Error vs Zenith Error

 

[PeterA]

This is geometrically impossible. It may appear this way because your magnifying power is insufficient to resolve it, but it is a geometric impossibility.

“Zenith” is NOT cantilever alignment. Zenith error correction and cantilever tangency are two very different and competing objectives. See here:
Sound Bite #36: Tracking Error vs Zenith Error

Thank you, J. R. I appreciate your expertise and deep dive into this subject. I’ve watched a bunch of your videos.

I realize that Zenith is not cantilever alignment. I do not have the tools to check how the stylus is mounted into the cantilever. I cannot see the cartridge facets lined up in the groove wall. I am also not aligning the cantilever on the protractor. My response was simply to state that the edges of the headshell or jig in my case, align with the tangent lines on my two point protractor suggesting proper alignment of the cartridge excepting inaccuracies of the cartridge construction. Of course this assumes the cantilever is straight in the cartridge body, and that the stylist is mounted correctly in the cantilever. I realize from your many posts that this is an assumption that should be approached with caution because you have documented many cases where the manufactured cartridge is not perfect or outside of tolerances. I know people can send their cartridges to you for measurements.

Is the geometric impossibility of alignment in my case due to the varying effective length with different cartridges and a fixed offset angle? If so how does one compensate for different mounting screw to stylus tip distances using an SME arm?

I understand that you can correct for a given effective length by using a slotted head shell. With a fixed pivot to spindle distance you can then use an arc protractor. I did this with a custom MINT LP protractor for my SME V12 arm. This device also showed cantilever alignment at the null point and was very effective. I read these are no longer made.

I had thought that SME, with its fixed mounting holes in the head shell allowed for proper adjustment by sliding the arm base thus adjusting the pivot to spindle distance. You can still use a two point protractor because two points define an arc of different radii. The relationship of the arc to the radius line of the LP will change slightly, if I understand this correctly.

In my case, both the head shell edges, and my jig edges appear to line up with the tangent grid lines at the null points at least according to the accuracy of eyes using my magnifying glass and good light. You are suggesting that this is not possible geometrically, and I would know that if my tools were better.

I’m sure the accuracy is only as good as the tools one uses. You have very good tools and can see and measure the various set up parameters with great accuracy.

 

[J.R. Boisclair]

Thank you, J. R. I appreciate your expertise and deep dive into this subject. I’ve watched a bunch of your videos.

I realize that Zenith is not cantilever alignment. I do not have the tools to check how the stylus is mounted into the cantilever. I cannot see the cartridge facets lined up in the groove wall. I am also not aligning the cantilever on the protractor. My response was simply to state that the edges of the headshell or jig in my case, align with the tangent lines on my two point protractor suggesting proper alignment of the cartridge excepting inaccuracies of the cartridge construction. Of course this assumes the cantilever is straight in the cartridge body, and that the stylist is mounted correctly in the cantilever. I realize from your many posts that this is an assumption that should be approached with caution because you have documented many cases where the manufactured cartridge is not perfect or outside of tolerances. I know people can send their cartridges to you for measurements.

Is the geometric impossibility of alignment in my case due to the varying effective length with different cartridges and a fixed offset angle? If so how does one compensate for different mounting screw to stylus tip distances using an SME arm?

An alignment template that uses the stylus position - not the headshell face(s) - as an alignment fiducial will mean that no matter your stylus run dimension (horizontal plane: stylus tip to center of screw holes), the P2S will be modified to ensure compliance with the chosen alignment scheme (Baerwald, etc.). This is true ONLY if the sliding axis of travel for the adjustable P2S keeps the spindle on the path.

I understand that you can correct for a given effective length by using a slotted head shell. With a fixed pivot to spindle distance you can then use an arc protractor. I did this with a custom MINT LP protractor for my SME V12 arm. This device also showed cantilever alignment at the null point and was very effective. I read these are no longer made.

Correct. They were a knock off of the original WallyTractor and did not include what I think is one of the most important "reference" features: the alignment points at max angular error pos and neg

I had thought that SME, with its fixed mounting holes in the head shell allowed for proper adjustment by sliding the arm base thus adjusting the pivot to spindle distance. You can still use a two point protractor because two points define an arc of different radii. The relationship of the arc to the radius line of the LP will change slightly, if I understand this correctly.

Correct. I should have articulated that the SME is unique in this way. The effective length is fixed by the pivot to center of middle of screw holes in headshell PLUS the stylus run (mentioned above). As I have seen stylus runs from 7mm to 14mm, this means your cartridge - your SPECIFIC cartridge - defines the effective length for an SME arm. You then modify the P2S distance in order to get whatever your eff. len. is to agree with the chosen alignment scheme

Running short of time. Sorry for short responses

 

[Atmasphere]

Ralph, you can disable the AS on your Triplanar by pushing the little black lever all the way up. This way it never touches the AS mechanism as the arm crosses the record. I have done this with each record I’ve played with the Triplanar for the last 20 years. It becomes second nature.

I was aware of that. In conversations with Triplanar (the owner was an employee of mine about 25 years ago) he mentioned that many users just don't put any weights on the anti-skate mechanism to good effect. I just followed his lead.

I start with the arm level. I can not adjust SRA or VTA at the headshell which would seem ideal, so I simple raise or lower the back of the arm.

One of the nice things about the Triplanar is the ability to set the VTA on the fly if you want. It has two graduated scales for this purpose; since LP thickness varies you can record and repeat settings for individual LPs (although its nothing I've ever done). Its a much more adjustable arm (which includes zenith) than the SME and has lower friction bearings too.

SRA is a bit trickier since the actual cutting angle of the cutter head is set to obtain the lowest noise groove rather than going for 92 degrees. The cutter stylus only goes about 10 hours before it needs to be replaced. My Westerex cutter head had to be removed from the mastering lathe to do this and that is true of the Neumann cutter as well. So there's a bit of setup required (including sorting out stylus temperature) to get the whole thing working again once the stylus is in place. As a result, the 92 degree SRA is really an approximation.

 

[PeterA]

An alignment template that uses the stylus position - not the headshell face(s) - as an alignment fiducial will mean that no matter your stylus run dimension (horizontal plane: stylus tip to center of screw holes), the P2S will be modified to ensure compliance with the chosen alignment scheme (Baerwald, etc.). This is true ONLY if the sliding axis of travel for the adjustable P2S keeps the spindle on the path.

Correct. They were a knock off of the original WallyTractor and did not include what I think is one of the most important "reference" features: the alignment points at max angular error pos and neg

Correct. I should have articulated that the SME is unique in this way. The effective length is fixed by the pivot to center of middle of screw holes in headshell PLUS the stylus run (mentioned above). As I have seen stylus runs from 7mm to 14mm, this means your cartridge - your SPECIFIC cartridge - defines the effective length for an SME arm. You then modify the P2S distance in order to get whatever your eff. len. is to agree with the chosen alignment scheme

Running short of time. Sorry for short responses

OK, thanks. My understanding seems correct, and I seem to have proper alignment, excepting the construction imperfections of the cartridge, ie the stylus in the cantilever, and the cantilever in the cartridge body. As I wrote earlier, I am very satisfied with my results using my DB Protractor and alignment jig and it seems to do a perfectly adequate job within the precision of my ability to verify. I guess that is now settled. I appreciate your responses.

 

[J.R. Boisclair]

One of the nice things about the Triplanar is the ability to set the VTA on the fly if you want. It has two graduated scales for this purpose; since LP thickness varies you can record and repeat settings for individual LPs (although its nothing I've ever done). Its a much more adjustable arm (which includes zenith) than the SME and has lower friction bearings too.

You are listening to changes in vector forces, not VTA, when you raise/lower the arm. I did a video on this too.

SRA is a bit trickier since the actual cutting angle of the cutter head is set to obtain the lowest noise groove rather than going for 92 degrees. The cutter stylus only goes about 10 hours before it needs to be replaced. My Westerex cutter head had to be removed from the mastering lathe to do this and that is true of the Neumann cutter as well. So there's a bit of setup required (including sorting out stylus temperature) to get the whole thing working again once the stylus is in place. As a result, the 92 degree SRA is really an approximation.

You are correct. I no longer weigh much importance to SRA for a number of reasons (which I also did a video about). Cutting angles can be way below 90 degrees but nothing is known about lacquer spring back and the "effective" cutting rake angle. In any case, in my video I share my doubt about why it may not be important anyway.

The 1981 article on SRA (the only one ever written) was hardly scientific and had a less than optimal control of variables which would affect the outcome. It deserves a real effort which we plan to give it next year.

 

[PeterA]

I was aware of that. In conversations with Triplanar (the owner was an employee of mine about 25 years ago) he mentioned that many users just don't put any weights on the anti-skate mechanism to good effect. I just followed his lead.

One of the nice things about the Triplanar is the ability to set the VTA on the fly if you want. It has two graduated scales for this purpose; since LP thickness varies you can record and repeat settings for individual LPs (although its nothing I've ever done). Its a much more adjustable arm (which includes zenith) than the SME and has lower friction bearings too.

SRA is a bit trickier since the actual cutting angle of the cutter head is set to obtain the lowest noise groove rather than going for 92 degrees. The cutter stylus only goes about 10 hours before it needs to be replaced. My Westerex cutter head had to be removed from the mastering lathe to do this and that is true of the Neumann cutter as well. So there's a bit of setup required (including sorting out stylus temperature) to get the whole thing working again once the stylus is in place. As a result, the 92 degree SRA is really an approximation.

Yes, I met a bunch of guys years ago in CT who all had the Triplanar arm. They loved it. The VTA on the fly is great as long as rigidity is not compromised. I have not owned or examined this arm careful to answer that.

I agree that SRA must be adjusted by listening, and that it varies by LP. I never followed MF's 92 degree compromise recommendation. Results all depend on how deep one wants to dive into it. There are tradeoffs. I respect people's various approaches and priorities.

 

[PeterA]

You are listening to changes in vector forces, not VTA, when you raise/lower the arm. I did a video on this too.

You are correct. I no longer weigh much importance to SRA for a number of reasons (which I also did a video about). Cutting angles can be way below 90 degrees but nothing is known about lacquer spring back and the "effective" cutting rake angle. In any case, in my video I share my doubt about why it may not be important anyway.

The 1981 article on SRA (the only one ever written) was hardly scientific and had a less than optimal control of variables which would affect the outcome. It deserves a real effort which we plan to give it next year.

J. R., are you suggesting that we not adjust arm height and listen to the results of these changes to vector forces? What is the alternative if one can not make the adjustments at the headshell or cartridge? I do not want to add shims to the interface of the cartridge and headshell, though I know this is what you do and sell. If we do not know the actual cutting angle and resulting groove profile each individual LP, to what standard are you creating the angles of your shims? In other words, what SRA angle are you targeting and correcting for when you examine a cartridge and making the shims?

I know that I and others do indeed hear improvements to the overall presentation of the music in our rooms when we fine tune arm height by listening. When it sounds right, it is audible and seems to matter for our enjoyment.

 

[Atmasphere]

The 1981 article on SRA (the only one ever written) was hardly scientific and had a less than optimal control of variables which would affect the outcome. It deserves a real effort which we plan to give it next year.

There are other studies about LP performance in general which are long accepted but as best I can make out are bad science.

A couple of examples:
"there is less resolution and or bandwidth near the center of the LP."
I found this to be highly questionable as I was able to cut a 30KHz groove in the runout area and play it back on a Grado Gold mounted in a stock Technics SL1200 I had found on craigslist. We used this turntable as a standard to let us know if a groove we cut was actually playable.

"LP distortion is quite high"
The Westerex 3d cutter system using the 1700 electronics wraps 30dB of feedback around the cutter head and the cutter amps have their own feedback on top of that. This makes for extremely low distortion! What this means is the playback is the source of 95% or more of the distortion; none of the 'distortion measurements' seen in studies take this into account. On top of that, problems in the phono preamp section can cause distortion (even ticks and pops that are not on the LP surface) yet no provenance is shown in these 'studies'.

Once I got my LP mastering system running, a lot of the 'limitations' of the LP I thought I knew died an ugly death.

The VTA on the fly is great as long as rigidity is not compromised. I have not owned or examined this arm careful to answer that.

FWIW the Triplanar arm tube is quite rigid and also internally damped. The SME arm is not damped and does benefit from it (which is why the Sumiko Analog Survival Kit was offered years ago). The problem doing using that kit (which is long nla) is you increase the mass of the arm which causes the ideal cartridge compliance to be a lower value.

You are listening to changes in vector forces, not VTA, when you raise/lower the arm.

I freely admit I've never tried to do that since LP thickness is quite variable. I've always set the cartridge up to the manufacturer's spec, which is usually the front of the cartridge being perpendicular to the LP surface (which means the arm tube will be parallel to the surface). I would usually use an LP that was 150gram, about 0.06".

 

[J.R. Boisclair]

J. R., are you suggesting that we not adjust arm height and listen to the results of these changes to vector forces? What is the alternative if one can not make the adjustments at the headshell or cartridge? I do not want to add shims to the interface of the cartridge and headshell, though I know this is what you do and sell. If we do not know the actual cutting angle and resulting groove profile each individual LP, to what standard are you creating the angles of your shims? In other words, what SRA angle are you targeting and correcting for when you examine a cartridge and making the shims?

I know that I and others do indeed hear improvements to the overall presentation of the music in our rooms when we fine tune arm height by listening. When it sounds right, it is audible and seems to matter for our enjoyment.

I am not saying not to do it, but what you hear has next to nothing to do with what it sounds like when you change VTA/SRA exclusively. I am encouraging people to stop referring to "VTA on the fly" with respect to lower/raising the arm because that false attribution will prohibit you from looking at each parameter for its individual impact to playback performance and therefore make far more difficult the goal of hitting the optimal angular range.

I weigh VTA far more heavily than SRA because we know for certain we can hear VTA changes. Any client of mine who has had 3, 4, 5 or more degrees of "butt down" has heard the extra clarity, focus, separation of instruments in the soundfield and overall increased sense of "rightness" associated with getting the VTA closer to 18 degrees or even less. They do NOT hear what you hear when you lower the arm too much. Those are the effects of multiple vector forces changing.

We KNOW what the vertical modulation angle is of Neumann, etc. after lacquer springback. We do NOT know anything about lacquer spring back effects on cutting rake angle and I raise doubts it matters much for playback rake anyway - this is particularly true with lower VTF playback and records with higher Shore D hardness ratings.

Unless you have a DaVa or one or two other very rare cartridges, your VTA is way too high. It is an industry problem. I discuss why the industry does this in a few videos.

 

[J.R. Boisclair]

There are other studies about LP performance in general which are long accepted but as best I can make out are bad science.

A couple of examples:
"there is less resolution and or bandwidth near the center of the LP."
I found this to be highly questionable as I was able to cut a 30KHz groove in the runout area and play it back on a Grado Gold mounted in a stock Technics SL1200 I had found on craigslist. We used this turntable as a standard to let us know if a groove we cut was actually playable.

AGREED

"LP distortion is quite high"
The Westerex 3d cutter system using the 1700 electronics wraps 30dB of feedback around the cutter head and the cutter amps have their own feedback on top of that. This makes for extremely low distortion! What this means is the playback is the source of 95% or more of the distortion; none of the 'distortion measurements' seen in studies take this into account. On top of that, problems in the phono preamp section can cause distortion (even ticks and pops that are not on the LP surface) yet no provenance is shown in these 'studies'.

AGREED!!!! Most "studies" have not properly controlled playback variables and therefore had poor conclusions of what the data was telling them.

 

[J.R. Boisclair]

I agree that SRA must be adjusted by listening, and that it varies by LP. I never followed MF's 92 degree compromise recommendation. Results all depend on how deep one wants to dive into it. There are tradeoffs. I respect people's various approaches and priorities.

Don't blame Fremer. Blame WAM Engineering (US!). Wally and I were highlighting the "importance" of SRA based on that article. With the support of my engineering team, we concluded it was not conducted well and was hardly peer reviewable as not enough detail was offered in order to test the reproducibility of the results.

Yes, we are at fault for making it "a thing", but we approach mechanical transcription for the science it is with far greater rigor now than we once did.

Now, once we do the real research on it and IF we find it is in fact very important and have reproducible data to prove it and publish that data, then I reserve the right to change my mind...again!

 

[PeterA]

FWIW the Triplanar arm tube is quite rigid and also internally damped. The SME arm is not damped and does benefit from it (which is why the Sumiko Analog Survival Kit was offered years ago). The problem doing using that kit (which is long nla) is you increase the mass of the arm which causes the ideal cartridge compliance to be a lower value.

Sorry, I was not clear. I mean the rigidity of the VTA on the fly mechanism. SME apparently did not do VTA on the fly opting for a more rigid coupling of the arm post to the armboard, if less convenient. I did not mean the Triplanar arm tube, and again, I have not closely examined the Triplanar arm. Those guys in CT all seemed to love it.

 

[Atmasphere]

Don't blame Fremer. Blame WAM Engineering (US!). Wally and I were highlighting the "importance" of SRA based on that article. With the support of my engineering team, we concluded it was not conducted well and was hardly peer reviewable as not enough detail was offered in order to test the reproducibility of the results.

Yes, we are at fault for making it "a thing", but we approach mechanical transcription for the science it is with far greater rigor now than we once did.

Now, once we do the real research on it and IF we find it is in fact very important and have reproducible data to prove it and publish that data, then I reserve the right to change my mind...again!

OK I gotta ask. There was this guy named Wally that used to live in this area (passed away a few years back) that had a protractor he was really proud of. He was always trying to convince us he was a champion tennis player and dancer. People wanted to buy his product but as best I can make out he really wasn't a very good businessman. He really didn't like what I had to say about SRA adjustments (which is what I've said here). One time he challenged me saying we didn't do any measurements to which I replied we looked for the lowest noise floor when setting up the cutter head. He insisted on taking that as if we had made no measurements... Did you take over his operation?

I mean the rigidity of the VTA on the fly mechanism.

Once you tighten the knurled screw down its quite rigid.

 

[J.R. Boisclair]

OK I gotta ask. There was this guy named Wally that used to live in this area (passed away a few years back) that had a protractor he was really proud of. He was always trying to convince us he was a champion tennis player and dancer. People wanted to buy his product but as best I can make out he really wasn't a very good businessman. He really didn't like what I had to say about SRA adjustments (which is what I've said here). One time he challenged me saying we didn't do any measurements to which I replied we looked for the lowest noise floor when setting up the cutter head. He insisted on taking that as if we had made no measurements... Did you take over his operation?

I did - along with his son who is also a mechanical engineer. I could not be doing what I am doing now with respect to exploring the performance limits of mechanical transcription without my relationship with Wally, but following his death and after conducting our own analyses I have diverged from a couple of his opinions. SRA is one of them.

 

[mtemur]

This is geometrically impossible. It may appear this way because your magnifying power is insufficient to resolve it, but it is a geometric impossibility.

You are wrong, @J.R. Boisclair — @PeterA is right. It is certainly and geometrically possible; maybe you misunderstood.

@PeterA is simply pointing out that an SME arm (or any sliding-base arm) alters the P2S distance by moving the tonearm base to match the specified overhang on the protractor. It does that while keeping the effective length constant. That’s where Peter is mistaken.

 

[J.R. Boisclair]

You are wrong, @J.R. Boisclair — @PeterA is right. It is certainly and geometrically possible; maybe you misunderstood.

Yes, I did misunderstand that the comment was being applied solely to an SME style adjustment system. I corrected myself above.

@PeterA is simply pointing out that an SME arm (or any sliding-base arm) alters the P2S distance by moving the tonearm base to match the specified overhang on the protractor. It does that while keeping the effective length constant. That’s where Peter is mistaken.

 

[mtemur]

Yes, different tonearm lengths can have different offset angles. If you draw a line straight back from the stylus through the offset and on into space and draw a line from the stylus to the cartridge pivot point (effective length), the angluar difference between the lines measured at the offset point is the offset angle. At least as I understand it.

View attachment 159846

I believe you are correct that the headshells for the 4Point and the 4Point 14 are different because of the different offset angles of the arms.

Wrt protractors I think it depends on the protractor. For example: the original Wally protractor is specific to the effective length and is thus arm specific. The newer Wally Universal Protractor v2 supports multiple effective lengths. The db Systems protractor supports multiple arm lengths. The Acoustical Systems Uni-Protractor from Dieter Brakemeir supports different length arms but will have a separate mirrored insert for each arm.

The thing, Linear Offset, you mentioned isn’t directly related to the offset angle on the headshell. Linear Offset is a result of the chosen geometry by the arm manufacturer. It’s directly linked to overhang, and only indirectly linked to offset angle.

• There is overhang on tonearms because it allows for two null points along the arc, which drastically reduces tracking error compared to having just one.
• There is an offset angle to reduce tracking error even further.
• In the drawing you shared, the vectors are drawn at one of the null points for simplicity. That’s the point where the offset angle corresponds with the Linear Offset distance. It doesn’t correspond at other positions along the arc.
• Finally—and more importantly—Linear Offset is a distance, which is why it’s expressed in millimeters. It’s also the cause of skating force.

Linear Offset isn’t some new concept—it’s been mentioned in SME arm manuals for decades. It may be mentioned in different names, but it’s the same thing. The longer the Linear Offset (and overhang), the higher the skating force.

 

[mtemur]

Good question - it depends on your approach to acceptable vinyl tracking error. SME is a fixed offset angle, fixed length arm with variable distance from pivot to platter spindle. It was originally supplied with a single point protractor - you would get zero tracking error at a fixed distance (around 66 mm , I think) and forget.

Using it with a double point protactor means you must find a point where the average errors at the two points is minimal - only by extreme chance you will get zero at both fixed points!

BTW, fixed offset angle tonearms are not acceptable for fans of tonearm alignment - the debates in the letters to editor in magazines between proponents of particular formulas in the 70's were as fierce as our current ones about vinyl versus digital - but we had to wait a couple of months between letters!
View attachment 159850

Here are the basic differences between tonearms for a given cartridge (or for a given distance from mounting holes to stylus):

• SME arms keep the Effective Length constant while altering the Pivot-to-Spindle (P2S) Distance.
• Arms with slotted headshells alter the Effective Length while keeping the P2S Distance constant.
• Offset angle is fixed on all of them (excluding tangential arms).

Even SME, or any other overhung arm supplied with a single-point protractor, still has two null points. You can clearly see this in the drawing you shared. They provide a single-point protractor purely for convenience, and it’s most likely based on Stevenson geometry.

All known geometries — Baerwald, Löfgren, Stevenson, and UNI-DIN — have two null points. Overhang and offset together enable these two points and inner and outer groove radii define where null points are located. That’s the essence of the overhung tonearm design — the most sensible, mathematically correct solution with the lowest overall tracking error. Tangential arms offer less tracking error but they're not sensible since they're the opposite of rigid.

There’s no “variable offset.” arm. All of the arms (conventional, pivoted) are fixed-offset tonearms.

However, regardless of the chosen geometry (Baerwald, Löfgren, etc.) in the tonearm’s design stage, you can still use whichever geometry you prefer — as long as the slots on the headshell allow it. In that case, the cartridge may appear slightly skewed to one side due to the different offset angle.

 

[Atmasphere]

Tangential arms offer less tracking error but they're not sensible since they're the opposite of rigid.

That was the advantage of the Rabco, although it might be a stretch to call it rigid. IMO/IME there was too much slop in the track and arm bearings.