Question on FR 66s

I think Bill's method is the only rational one for use with fixed headshell cartridges like the SPUs and FR-7 types.
Yes.....the off-set angles may be slightly different to the prescribed ones at the null points......but only by 1 or 2 degrees in most cases?
If you can align your styli to all be 'visually' within these limits......I'd suggest you're doing alright?
That's why I recommended to Chris to check the geometry of the stylus at the null points after adjusting the arm to follow a preferred arc geometry as Bill does.
John appears to be offering no solution at all......and if he thinks the UNI-protractor uses Baerwald alignment.....I believe he is mistaken?
Dertonarm has developed his own alignment called UNI-Din which places the null points differently to the others.
He also recommends moving the FR-64s tonearm to a S to P distance of 231.5mm rather than the recommended 230mm.
As he is a rather renowned fan of the FR-7 series of cartridges.......I can't imagine him sabotaging these cartridges with damagingly incorrect off-set angles?

Bill,

With the UNI-Pro, if I set the tonearm to SME's prescribed P2S and check alignment with the Baerwald template, which Daniel says is the one to use with the SME, it's way off, as one might expect. So, I can slide the SME along its base, changing P2S until the stylus drops in the template's hole. But then offset angle is wrong because the orientation of the template itself is no longer proper, seeing as how has been situated in relation to the prescribed P2S.

The Uni Protractor functions in the same way as the Dennesen - the principle does not require the actual dimension in millimeters of P2S distance to be known. It is irrelevant to the principle, and for some arms with sliding or movable bases like the SME, saying that it is necessary to measure P2S is just plain wrong. It is not my opinion, just a fact.

The micrometer function adjusts for the different alignment options and, if it is set for LofgrenA/Baerwald IEC, then, just like the Dennesen, when the movable arm is correctly positioned over the tonearm pivot point, the null is correctly orientated, and the cartridge should line up with the grid lines.

SME give an effective length dimension, but it is nominal, based on a notional standard cartridge mounting hole to stylus dimension. And the related P2S refers to this. The SME sliding base accommodates variations in cartridge dimensions (which alter the effective length and cartridge offset), thus allowing your SPU to be set up correctly even though is has no adjustment.

However, I assume that the setting on the Uni-Pro's micrometer has been determined according to the manufacturer-specified P2S.

The micrometer setting relates only to the particular alignment (LofgrenA, B Stevenson) which is initially derived from the inner and outer recorded radii (IEC, DIN etc), which gives rise to fixed numbers for the linear offset and the nulls, which in the case of your arm (and any other using that alignment of whatever effective length), LofgrenA/Baerwald IEC.

It is easy to get lost in all this stuff. And I know there are many people confused by it, which is why I try to comment when I see misunderstandings.

Regarding the SPUs, the fact of differing compliances might cause slight variations as VTF and VTA change when changing from one to another. How much of a variation is there in effective length?

John

John

Thanks for the explanation. I stand corrected on the relation between P2S and alignment using the UNI-Pro, and on how the micrometer settings are determined. I had concluded (erroneously, it turns out) that they were related because the UNI-Pro requires centering over the pivot, which, in turn, has typically been located according to the manufacturer's prescribed P2S. I use the UNI-P2S, which is extremely handy.

As I recall, the variation between the SPU Royal GMII and Mono GMII is tiny--easily less than 1 mm off the arc. But that's too much.

I hadn't thought of it as a VTF and compliance issue. Could be. The differences between the two SPUs are a non-negligible half a gram in tracking weight (3g for the Royal v. 3.5g for the Mono) and 4 µm/mN in compliance (8 v. 12). I imagine that the extra weight and higher compliance of the Mono could cause it to splay, pushing the stylus beyond the arc, which is the direction of the error. That's a very good point.

Still, I've felt more comfortable--and gotten better sonic results--using the arc protractors on this arm with SPUs. After this discussion, though, I'll experiment further with the UNI-Pro.

Apologies to the OP if I've pulled the thread off topic.

Bill

John, Is it not the case that for your statement that the P2S is irrelevant for the Dennesen or the UNI to be true, the cartridge must be aligned (ideally) perfectly with the long axis of the headshell. If the cartridge is "twisted" inward or outward with respect to the headshell, then the P2S dictated by the alignment grid on the template surface would put the pivot at some position different from ideal. I guess this would still "work", in the gross sense of the word, but if you want highest precision for a particular specific classic geometry, what I say must be true. Yes?

Of course, for an SPU cartridge, the point I raise is moot.

Halcro,
Yes you are correct: the only way to adjust cartridges like the SPU on arms like the FR64 and 66 is at the base, as the headshell offset is fixed. Which is why on a specific arm you have to use the existing specific arm alignment which uses that headshell offset. In other words, the given nulls. Only by doing this will the cartridge line up correctly.

John appears to be offering no solution at all......and if he thinks the UNI-protractor uses Baerwald alignment.....I believe he is mistaken?

The solution I gave for SPUs is straightforward: adjust the base to fit the original nulls. Don't use an arc.

If you have two SPUs or FR7s or whatever, and they don't have the same dimensions, then the base has to move or you accept a compromise.

For removable headshells with slots, you can use whatever alignment you like, but as I have told you in a past post, if you want to swap with an SPU you have to set it up first, and only then use a slotted headshell to mount and adjust another cartridge, without moving the P2S.

and if he thinks the UNI-protractor uses Baerwald alignment.....I believe he is mistaken?
Dertonarm has developed his own alignment called UNI-Din which places the null points differently to the others.

You are right to question your belief ;-)
As it is the Uni (for universal) protractor, DT has incorporated an adjustment to allow different alignments, one of which is LofgrenA/Baerwald IEC, and another is his version of LofgrenA which is derived from inner and outer recorded radii parameters which differ from IEC and DIN, thus giving different nulls. In the case of the SPU, unless the arm has an offset which corresponds to that alignment, then the alignment can never be achieved, and the cartridge will only ever align at one null. That is the way it is. All else is compromise. Whether the compromise is to accept a misalignment of a couple of degrees is up to you.

In the case of the FR66 the original P2S and overhang seem fine to me. A change to 296 makes little difference. Nulls around 63 and 115 would work ok. The thing is to get the offset as accurate as possible, as this is the parameter most prone to error.

John