Grado "wobble"...?

I should probably clarify a few things. First, the cartridge wobbles only rarely: three records so far, out of several thousand. On all the others it performs far better than a $40 cartridge has any right to.

Also, I've tried to find some common denominator regarding these 3 records but have come up with little so far. Each has a very slight bit of warp, but no more than many others in my collection. Two are 45 RPM, one is 33 RPM. None has vast dynamic shifts. But these 3, for whatever reason, all cause the cartridge to wobble every time I try to play them, while (so far) no other records in my collection seem to. And one of these records (I don't recall playing the other two) played fine, no wobble, when the cartridge was in the Thorens arm.

Thanks for the tip regarding this question at Vinyl Asylum.

Hmm. Though I know very little about this stuff and am highly math-phobic, I ran a calculation according to the figure on Galen Carol's "tonearm/cartridge capability" web page and came out with a resonant frequency of 8.635, which though lower than the recommended 9-11 range doesn't seem to miss by much. I didn't think the Grado's compliance of 20cu was considered "low." But admittedly I have a lot to learn in this regard. Thanks for all the help so far.

OK, I've had a chance to look through the archives at VA, and am more confused than ever. Some posters there suggested that the wobble was due to unclean vinyl (my soul, perhaps, but never my records). Others suggested that the VTF was set incorrectly (I'm at 1.55g; Grado recommends 1.5). Still others suggested that the 'arm/cartridge match was improper. This last point is what has me still concerned.

Factoring in an effective mass of ~16.5 grams (11 g for RB-250, 5.5 g for cartridge, plus some miniscule amount for two mounting screws), and Grado's published rating of 20 cu for the cartridge, I calculated the Grado/Rega resonant frequency at about 8.6 Hz. The chart at the bottom of Van den Hul's phono FAQ webpage essentially confirms this.

Is this really too far outside the recommended 9-11 Hz range?

And, isn't the problem that the Grado has slightly too *high* a compliance for my 'arm, rather than too *low* a compliance?

It seems that Jlazart's recommendation of a total effective mass of ~14 g is spot-on, but also that I'm in the ballpark. So I have to think the Grado wobble (or wiggle) is due to something other than 'arm/cartridge matching, at least in my case. (My latest theory is that the slightly wider grooves of a 45 RPM pressing and/or the wider lead-in grooves prove difficult for the Grado to track.)

I'll certainly look for something a bit lower in compliance when I upgrade (soon).

Thanks again. Sorry to beat this topic to death--just trying to learn something from it.