Question on FR 66s

Chris,

The issue about P2S and overhang using SPUs is something I've also struggled with using my SME M2-12R. Especially aggravating is the small de facto variance among SPUs that purport to have the same overhang. I read surprisingly little conversation about this issue, which will wreak havoc if one's armboard and tonearm-mount are unmovable.

I do what Henry recommends, which is to adjust P2S so that the SPU aligns with my selected geometry. Fortunately, the SME has a sliding mount; otherwise I'd be out of luck. I use arc protractors from MintLP and Accutrak, and I'm able get the stylus to track the arc almost perfectly. The UNI-Pro, which I also have, doesn't really work in this instance because it is contingent on a prescribed P2S.

Bill

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

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