Question on FR 66s

Hi Bill, thank you for your recommendation. It appears to me that the manufacturer specified S2P distance is not some kind of "holy grail" that cannot be touched by mere mortals.
According to an geometriy calculator as supplied by Vinyl Engine you can calculate the distortion if the geometry is changed.
If I change the S2P distance to 297 mm (instead of 295 mm) and the overhang can be kept at 12 mm, I would end up with reasonable distortion. But you will deal with other null points!

Chris

Chris,
If you change the mounting distance to 297mm it will be fine if this gives a 12mm overhang. If you are using an SPU the headshell offset is fixed, so the only variable is P2S.

If the arm was designed for a 50mm as opposed to 52mm pickup, then the real effective offset will be slightly less as the effective length increases, but the basic arm geometry remains the same, it just needs more P2S distance. You can use the original protractor to check, as the nulls will be the same.

John

Hi John,

Yes, I've come to accept that the offset angle will be a little off using my arc protractors, both of which are designed for Baerwald, with the SME and SPUs. I just don't see any way around it. It seems to me that SPUs are inherently compromised in this regard--and inconsistent. For example, if I set the P2S to enable my Royal GMII to trace the Baewald arc and then swap on my Mono GMII, the Mono is slightly off, which I read as overhang inconsistency.

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. And because the UNI-Pro is orienting the stylus using a single point rather than the multiple points available using the arc protractors, I trust it less--unless its controlling parameters like P2S remain fixed.

I suppose I could reorient the template and further change P2S until the stylus drops in the hole and the cantilever looks aligned (which I would take to mean offset angle is correct). However, I assume that the setting on the Uni-Pro's micrometer has been determined according to the manufacturer-specified P2S. Is this not so? Then changing the P2S scrambles this variable, too, doesn't it? With these two primary coordinates thrown to the wind, this alignment procedure seems rather random and chaotic.

But I'm certainly no expert in these matters, just a guy wrestling with SPUs and alignment tools in hopes of good sound, so please correct me if I'm not seeing things correctly.

Hi Chris,

Yes, that's what I've come to accept by shifting the P2S: slightly different null points and slightly incorrect offset angle in exchange for minimal overall distortion. I just don't see another way with SPUs.

Bill

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