Question on FR 66s

Hi Lewm
The Dennesen principle allows any arm to align to LofgrenA/Baerwald.

If the arm is designed to that alignment to begin with and is mounted at the correct P2S the cartridge will align with the grid when square in the headshell.

If the arm is mounted with P2S incorrect or is designed with a different alignment (say, Stevenson) it can still be aligned if it has the facility ( ie has slots) to move the cartridge to the correct offset and effective length to align with the grid.

In the case of Dertonarm's variant, various alignments are possible. The physical structure of the arm's headshell doesn't matter if it allows twisting by a few degrees and some fore and aft movement.

The way it works is that the protractor alters the angle of the grid relative to the arm pivot automatically as the sliding arm is moved back and forth, because their relationship is fixed for whatever effective length. So if the arm pivot is in a fixed position, the only adjustment available is to twist and slide the cart to obtain the correct offset and effective length for the fixed P2S whatever it is.

John

Bill, John, Lew and others, I would like to have your opinion about the following calculations I made regarding the geometry of the FR-66S with a SPU (52 mm length). Please correct me if I'm wrong.
The effective length of the FR-66S with needle to arm distance of 50 mm is 307 mm.
Draw a imaginary line (line 1) between the needle and the pivot, which is the same as the effective length.
Draw another line (= line 2) from the needle, parallel to the head shell.
Between line 1 and line 2 there is an angle, which is the offset angle (16.8 degrees for the FR-66S).
So the projection of line 1 on line 2 is cosine of 16.8 degrees * 307 mm = 293.9 mm (right triangle).
293.9 mm + 2 mm (because the length of the SPU is 52 mm) = 295.9 mm.
The new effective length will be: 1/cosine 16.8 degrees *295.9 mm = 309 mm.
If we want to have an overhang of 12 mm, the P2S distance would be: 309 mm - 12 mm = 297 mm.

Chris

Halcro,
As an aside, if Dertonarm's recommending setting the P2S at 231.5mm for the FR64 with FR7, that presumably means that when using the FR7 pickup, the effective length is changed as is the cartridge offset, and he reckons that is the best way to adjust for that, using the reduced offset and increased overhang to allow alignment at different nulls of around 63 and 115. Simply changing the P2S if the effective length remains the same is not a good idea with an integrated cartridge.

A friend of mine has pointed out that these discussions as to P2S distance for integrated headshell pickups would be moot had the FR arms been designed with sliding bases like the SME. Perhaps someone will put one on the market, like the aftermarket adjustable VTA base which I believe was available, and put FR owners out of their misery...?
John

Hello John_Gordon,

I do like the way that your mind works through these well thoughout solutions...scientific, without a hint of marketing, thank you!

Cheers

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?

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.

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.

Having been listening to FR 66s for the last couple of months with a few cartridges, I think that it is definitely outstanding for low compliance high mass cartridge. In my system, Koetsu Coralstone and Ikeda Kai sounded exceptional.
I tried Koetsu with JWM 10.5, TW 10.5, Graham Supreme 12 inch, Reedd 3Q and heard it with Vyger linear tracker, current version of Triplanar in other systems and none came close to what FR 66s can do with Koetsu. I prefer Air Tight PC-1 supreme with Reed, Dynavector XV-1s with Graham. Both work well with FR 66s as well but not on the same performance plane as Koetsu and does not outperform other arms in my system. I only try Ikeda Kai with FR 66s so far and it really sings such that I have no urge to hear it with another arm just yet.

@suteetat 
I read on this thread that you have a few protractors including a clearaudio and have an FR64 arm.
I have both the FR64S and a Clearaudio protractor. Using the 231.5 Bearwald pivot to spindle length my cartridge fully forward in the ehadshell still does not reach the little circle for the stylus. If I use 230mm I can - just. I've read that the Clearaudio is very similar to Bearwald - is that correct, or did you have the same issue finding that you had insufficient headshell to get the right overhang

thanks

Using the 231.5 Bearwald pivot to spindle length my cartridge fully forward in the ehadshell still does not reach the little circle for the stylus.

It depends on the cartridge mounting slots and your headshell size and slots size too (jelco), your cartridge is Denon 103 designed in the 60’s.