Pivot to stylus spec. of tonearm?

[cgallery]

Before I go any further, I want to thank everyone for all the help that has been provided me on my tonearm questions. You guys have been extremely helpful.

I've been looking a lot at the SME Series V (they seem to know what they're doing).

https://sme.co.uk/audio/product/series-v/

I'm trying to sort of copy their measurements, as a good starting place for my own arm.

They specify a "distance from pivot to stylus" of 233.15mm.

The drawing would seem to indicate holes and not slots for cartridge mounting. I don't think the wand slides in the pivot (but I could be wrong).

So how do they know that the stylus will be 233.15mm from the pivot, don't cartridges vary in the spacing of the stylus to the mounting holes? Or is that spacing a standard?

 

[mkane]

My interpretation would make me believe it doesn't matter what cartridge you use. That distance will give you the correct overhang.

 

[cgallery]

My interpretation would make me believe it doesn't matter what cartridge you use. That distance will give you the correct overhang.

Is there a standard for 1/2" cartridge geometry? Maybe the the horizontal measurement from the diamond to the mounting screw positions is a standard I don't know about?

 

[cgallery]

I found this:

Cartridge installation begins by affixing the cartridge body to the tonearm headshell. Tonearm headshells typically contain either slots or holes through which screws (usually supplied with the cartridge, and should be of the non-magnetic variety) may be passed into the cartridge body. Slotted headshells allow for the position of the cartridge to be adjusted for correct alignment. Headshells containing fixed-position holes (such as those of the venerable Rega RB300 and Naim Aro) assume that the geometry of the partnering cartridge is such that correct alignment will be achieved using the holes supplied. Unfortunately, tonearms whose headshells contain fixed holes will not allow for correct alignment of all cartridges . They do, however, make setup of compatible cartridges relatively simple (tonearm manufacturers who advocate fixed-hole headshells usually have a particular cartridge, or set of cartridges, in mind at the time of design – namely their own or those of a manufacturer whose products are believed to work well with the arm in question).

Source: http://www.audiophilia.com/reviews/2016/1/17/a-beginners-guide-to-cartridge-setup

So I guess I should lookup compatible (to the SME V) cartridges, and try to determine the measurements of those?

 

[mkane]

 

[cgallery]

Reading through the SME manual a little more carefully, they indicate that most cartridges have a stylus to fixing hole distance of 9.5mm (.375").

So that is what I'll use as well.

 

[tabarddn51]

If you are going to make your own arm then go 12".
Pivot to stylus distance is not that important, what is important is setting the arm / cartridge up correctly the distance you have when you have completed your project. Also when designing an arm you need to ensure the Eff Mass is correct for the cart you what to use. SME V's are quite good arms, but there are many better & cheaper.

Cheers

 

[marcmorin]

Reading through the SME manual a little more carefully, they indicate that most cartridges have a stylus to fixing hole distance of 9.5mm (.375").

So that is what I'll use as well.

they may have meant most cartridges from "manufacturer X" have a distance of 9.5mm.

 

[WaynerN]

The more important distance is the tonearm pivot center to spindle center distance, which for the SME arm is 215.35mm. That produces a Lofgren A (Baerwald) alignment (IEC). This produces a 17.790mm overhang with a 23.629° offset angle, provided that the cartridge you pick conforms to the stylus to mounting hole centers.

To be in the Lofgren A (Baerwald) alignment, all 3 perimeters must be met: 215.35mm spindle to pivot distance, 17.790 overhang, and 23.629° offset. If any of these numbers drift from theoretical perfect, the tracking error will increase, so it is very it is very important that care is used in doing an alignment.

I personally do not like arms with fixed mounting holes. They inhibit freedom of choice for the user. The Rega arms have a center hole and 2 slots to align their cartridges to their arms installed in their tables. It's done for simplicity, user wise. They provide 2 slots for the "other" guys that want their own alignments (Stevenson, Lofgren B, etc.).

 

[bimasta]

It doesn't matter where the stylus is in relation to the cartridge mounting holes. The measurement of Pivot-to-Stylus only measures where the stylus is — the cartridge body is irrelevant. It's annoying that cartridge makers just "do their own thing" when there could be a standard, but it doesn't matter.

The P-to-S measurement is called "effective length". It's determined by the tonearm designers: with the stylus in that position, the geometry is right. If the tonearm is mounted in the correct spot on the turntable (to the millimeter and degree °), effective length is all you need adjust.

 

[cgallery]

Well, I moved away from the aluminum tube arm. Just too many issues w/o a lathe.

I've decided on going back to wood and/or carbon fiber. Maybe aluminum with a weight-reducing pattern cutout.

Current generation pictured. I'm waiting for supplies from McMaster (I cobbled this together with parts from a local hardware store that has a limited selection).

The current arm's important dimensions are copied from the SME V. So the cartridge mounting holes are at 23.635 degrees, the pivot to stylus is 213.15mm.

I've ordered both aluminum and stainless threaded spacers from McMaster, which should allow me to change the response of the tonearm quite a bit. With the spacers ordered, I'll be able to change the height from 1-1/2" to 2" (in the pic it is 1-1/4"). So aluminum and stainless in two sizes should allow me quite a bit of flexibility.

I ordered a rod-end bolt (https://www.mcmaster.com/2434K35) for the counterweight. So basically this will be between a 1/4" high bottom spacer and the top spacer (either 1" or 1-1/2"). To adjust azimuth, I should be able to adjust the counterweight left/right.

The slots in the top are to secure the wiring. The shielded wire will run down the middle of the top, and then dive under via that last wider slot.

Should be very easy for me to make arms of any length I like. I'm starting with the proportions of the SME because I had to start somewhere, and I'm hoping for some early success to keep me going.

 

[cgallery]

Oh and I'm also going to need to make something along these lines...

 

[bimasta]

View attachment 1582222
Should be very easy for me to make arms of any length I like. I'm starting with the proportions of the SME because I had to start somewhere, and I'm hoping for some early success to keep me going.

For all it's simplicity it's very attractive. Maybe because of its simplicity. Is it a working model, or a design prototype?

I made a tonearm years ago. 12", so I used the SME 3012 specs. The offset angle is different at that length, around 17°; 9" arms are around 23°. But I couldn't drill the holes as accurately as SME (hand-drill) and it was a bit off.

I found a document online from the US Patent Office. It was a table showing the offset-angle for every length of tonearm, by 1 millimeter increments, so it covered every conceivable length. I was thrilled to see that my hand-drilled holes were spot-on. It was sheer chance: I didn't get the length exactly the same as SME, and my erroneous offset angle was just right for the length I ended up with.

Two wrongs made a right.

 

[cgallery]

For all it's simplicity it's very attractive. Maybe because of its simplicity. Is it a working model, or a design prototype?

I made a tonearm years ago. 12", so I used the SME 3012 specs. The offset angle is different at that length, around 17°; 9" arms are around 23°. But I couldn't drill the holes as accurately as SME (hand-drill) and it was a bit off.

I found a document online from the US Patent Office. It was a table showing the offset-angle for every length of tonearm, by 1 millimeter increments, so it covered every conceivable length. I was thrilled to see that my hand-drilled holes were spot-on. It was sheer chance: I didn't get the length exactly the same as SME, and my erroneous offset angle was just right for the length I ended up with.

Two wrongs made a right.

Once I have the right spacers and the rod-end, it should go on to be a working model. But first I'll have to assemble the platter/motor so I can start testing.

I do think it has potential for looking kinda neat. I'll use colored crochet thread to secure the wiring to the arm (using those slots). The spacers (aluminum and/or stainless) and the stainless rod-end (for the counter-weight) should jazz it up a little, too.

And you're right on the two wrongs making a right, that has gotten be out of the fryer more than once!

I'll post pictures of my progress. I'm sure I'll have a lot more questions.

Oh and BTW, the wand is easily replaceable. So if I want to try a longer arm, I can just cut one and swap it out. I'd just have to adjust the pivot location but I can likely have a single table with multiple pivot locations, it just needs a 1/4-20 hole. Perhaps when I make the base of my table, I'll drill a row of holes for arms of various lengths.

 

[bimasta]

I didn't read your post #11 closely enough, sorry. It's all subjective and it's your baby. But the wires on top? Colored threads? It's so simple and clean now and for me that's a big part of the appeal.

"Oh and BTW, the wand is easily replaceable. So if I want to try a longer arm, I can just cut one and swap it out... et al..."

You'll also have changeable arms, with cartridges firmly mounted — much better than swappable h'shells and connectors with "play" and lots breaks in the line.

I'd like to see more angles, details. Its simplicity seems to conceal some ingenious touches, such as the pivot and c'wt. If you prefer to keep them secret I get it.

Do you plan to add some kind of cueing thingie?

 

[cgallery]

I didn't read your post #11 closely enough, sorry. It's all subjective and it's your baby. But the wires on top? Colored threads? It's so simple and clean now and for me that's a big part of the appeal.

"Oh and BTW, the wand is easily replaceable. So if I want to try a longer arm, I can just cut one and swap it out... et al..."

You'll also have changeable arms, with cartridges firmly mounted — much better than swappable h'shells and connectors with "play" and lots breaks in the line.

I'd like to see more angles, details. Its simplicity seems to conceal some ingenious touches, such as the pivot and c'wt. If you prefer to keep them secret I get it.

Do you plan to add some kind of cueing thingie?

The wiring can go on either side, I just think it would look neat on top. We will see.

I'll post better pictures once I have the other parts from McMaster, so the counterweight and azimuth adjustment are working properly.

 

[tabarddn51]

Gentlemen, It is virtually impossible to get the correct overhang with fixed cartridge mount holes & a fixed arm position. That is because the cartridge mounting point to stylus point varies to much from manufacturer to manufacturer, as much as 18 mm. So unless you are very lucky you are pissing into the wind, as they say. Because of the 18 mm possible variance it is also very difficult to set the correct offset angle, which is even more important to get right that the overhang. Possibly the only way to get these factors right is only drill one mounting hole in the centre on the arm tube & have a cartridge carrier headshell as they do with Temaad Arms. Then all you need to do is determine what your pivot point to stylus is, then you can print out a unique set up template. I always use the one kindly provided by Conrad Hoffman.

http://www.conradhoffman.com/chsw.htm

However you will most likely find that you need to move your arm, with is normally as simple as making a slot in you arm board.
I recently mounted a refurbished 11" Grace 707 arm on a Rega T/T using this method.

Cheers

 

[cgallery]

Gentlemen, It is virtually impossible to get the correct overhang with fixed cartridge mount holes & a fixed arm position. That is because the cartridge mounting point to stylus point varies to much from manufacturer to manufacturer, as much as 18 mm. So unless you are very lucky you are pissing into the wind, as they say. Because of the 18 mm possible variance it is also very difficult to set the correct offset angle, which is even more important to get right that the overhang. Possibly the only way to get these factors right is only drill one mounting hole in the centre on the arm tube & have a cartridge carrier headshell as they do with Temaad Arms. Then all you need to do is determine what your pivot point to stylus is, then you can print out a unique set up template. I always use the one kindly provided by Conrad Hoffman.

http://www.conradhoffman.com/chsw.htm

However you will most likely find that you need to move your arm, with is normally as simple as making a slot in you arm board.
I recently mounted a refurbished 11" Grace 707 arm on a Rega T/T using this method.

Cheers

I'm going off what SME indicated in their manual (in my post #6,) where their arm is intended for cartridges with a 3/8" stylus to fixing hole distance. I figured that would be a good place to start.

It will be interesting to see how closely the cartridge I order matches that 3/8". I'm going to start with a cheapie Audio Technica (so I don't destroy a good cartridge). 3/8" I believe is the Audio Technica standard, so we shall see.

Seeing as I've had better than anticipated luck keeping my center of gravity quite low, my V2 will attempt to tighten the stylus to pivot offset with some changes to the wand design. That will also be a good time to accommodate some adjustment in the overhang/angles if I find this arm has promise.

 

[bimasta]

Gentlemen, It is virtually impossible to get the correct overhang with fixed cartridge mount holes & a fixed arm position. That is because the cartridge mounting point to stylus point varies to much from manufacturer to manufacturer, as much as 18 mm.

I'm going off what SME indicated in their manual (in my post #6,) where their arm is intended for cartridges with a 3/8" stylus to fixing hole distance.

Tabarddn is correct. One could make such an arm to suit a single cartridge (3/8"), and then find others that fit; but many or most carts won't. SME added a sliding-base, at considerable cost, to adjust for the differences. SME thus keeps the offset angle constant, while headhsell-slots change it by changing P-to-S distance.

I'm intrigued by "as much as 18mm". Which cartridge has so big a distance between stylus and mount holes? Curious, I measured a few of my carts at random. Three had a total body length of 18mm; two were 19-20mm body length; Koetsu R'wd Longbody was longest, as it's name suggests, at 29mm. But none had Stylus-to-Holes distance exceeding 9mm, most were less. Your 18mm cartridge S-to-M seems very exotic. What is it?

 

[cgallery]

Tabarddn is correct. One could make such an arm to suit a single cartridge (3/8"), and then find others that fit; but many or most carts won't. SME added a sliding-base, at considerable cost, to adjust for the differences. SME thus keeps the offset angle constant, while headhsell-slots change it by changing P-to-S distance.

I'm intrigued by "as much as 18mm". Which cartridge has so big a distance between stylus and mount holes? Curious, I measured a few of my carts at random. Three had a total body length of 18mm; two were 19-20mm body length; Koetsu R'wd Longbody was longest, as it's name suggests, at 29mm. But none had Stylus-to-Holes distance exceeding 9mm, most were less. Your 18mm cartridge S-to-M seems very exotic. What is it?

Right, but as I indicated in my post, adjustment will come later.

You have to start somewhere, can't get bogged down in every detail.