Question on FR 66s

Thanks, John. As it happens, I own both an original metal Dennesen and a UNI. I tend to use the Dennesen only to set P2S. (I mark the desired distance on a piece of white paper and then set up the Dennesen so its pointy end is on one mark and the center of the spindle hole is over the other mark. Then set the adjusted Dennesen on the spindle and "Bob's your uncle".) I don't like using it for cartridge alignment because I have a very difficult time seeing its grid and sensing the position of the little dimple that marks the target for the stylus tip. (Also, many of the vintage Japanese tonearms are not meant for Lofgren A.) The UNI is a little better for that purpose. As I mentioned privately, I have a bias against twisting the cartridge in the headshell, based on one bad experience doing that. So I tend to favor using the geometry for which a particular tonearm was designed.

John,
If one were to do the calculations as you suggest......with and SPU or FR-7 type of fixed headshell......surely the Off-Set angle cannot be changed?
Nor can the Overhang or Effective length.
The only parameter able to be changed is the Pivot to Spindle distance?
To calculate the new P to S....one needs to know accurately (to within 0.1mm) the 'actual' Overhang Distance.
To do this with a 'J' shaped tonearm like the FR-66s.....one needs to set up the arm accurately to the recommended P to S Distance (295mm) and then measure the stylus point Overhang?
One would imagine that the FR-7 series (because they are made by the same manufacturer as the tonearm) would be spot-on the specified 12mm?

The problem that Jazzdax poses

The length of the SPU is 52 mm instead of the 50 mm recommended by Ikeda.

does not necessarily indicate a 2mm difference in stylus Overhang?
One would need to accurately measure this as I describe..... before plugging those figures into the Vinyl Engine Calculator to ascertain the new P to S distance and the consequent new Null Points with the accompanying distortion figures.

There must be a way....but for the life of me I can't see a way to accurately measure this Overhang to within 0.1mm?

Thuchan has a fine collection of SPU cartridges.
I suspect he uses his original Ortofon tonearm to run them?.........but I wonder how he sets their geometry and whether he has mounted them in the FR-66s?

Chris,
Your new P2S would be fine. To get the new effective length it is more useful to also take 307 * sine 16.8, as this gives the linear offset, which is a constant for any particular alignment, and doesn't change when using integrated headshell cartridges. Not that it makes much difference to the calculation, except to illustrate the change in cartridge offset as the effective length increases. You can get more of a sense of this if you imagine an elongated SPU with stylus at say 200mm. The headshell offset of the arm doesn't change -it is still 16.8 - but the angle between the plane of the cantilever and the arm pivot would be much much reduced as the effective length increases.

In your case, 307* 0.289 = 88.73mm. Together with your new extended third side at 295.9 this gives (by Pythagoras) the new effective length of 308.9mm and an effective offset of 16.69 degrees. A 12mm overhang would be a good choice. To maintain the original alignment it should be trifle less, but it is neither here nor there. As you say this gives a P2S of 296.9mm /297mm.

Halcro,

If one were to do the calculations as you suggest......with and SPU or FR-7 type of fixed headshell......surely the Off-Set angle cannot be changed?
Nor can the Overhang or Effective length.
The only parameter able to be changed is the Pivot to Spindle distance?

The offset changes as the effective length increases, and overhang is simply what is left after P2S is set, or vice versa.

Ideally, you are correct in saying that one should measure the actual effective length if you wish to set an exact P2S for a particular alignment. Alternatively with a sliding base this is not necessary, as the P2S will be correct when the cartridge is aligned with the arm's two original nulls.

One would imagine that the FR-7 series (because they are made by the same manufacturer as the tonearm) would be spot-on the specified 12mm?

One would hope so, though I don't know, in which case altering the P2S would not be a good move.

The problem that Jazzdax poses
The length of the SPU is 52 mm instead of the 50 mm recommended by Ikeda.
does not necessarily indicate a 2mm difference in stylus Overhang?
One would need to accurately measure this as I describe..... before plugging those figures into the Vinyl Engine Calculator to ascertain the new P to S distance and the consequent new Null Points with the accompanying distortion figures.

The thing to realise is that it is effective length that increased by 2mm if that is the case. The overhang is the effective length minus the P2S, whatever it is. With a slotted headshell, if effective length varies, then because P2S is fixed, overhang varies. With a sliding base, if P2S varies, then because effective length is fixed, overhang varies.

Unoear,
Thanks for that.
John

One way to deal with SPU cartridges and its alignment is to remove them from their SPU headshell and go nude. They are aftermarket adapters (though hard to find) that will allow a nude SPU to mount to a slotted headshell. Unfortunately, you don't have this option with the FR7s since they can't be removed from headshell.