Shelter 501Mk2 or ZYX R100-02H

Cartridges of 22-30cu compliance tend to perform best on fairly low mass tonearms. That is not the case with a ZYX. On a low mass arm (say < 10g eff. mass) a ZYX tends to sound lifeless and bass shy. Instead of the arm stabilizing the cartridge, the (relatively stiff) suspension wags the arm.

ZYX's sound best on mid-weight tonearms, roughly 11-20 grams or so. Optimal performance (fullest bass and dynamics without overdriving the cantilever) seems to occur on arms in the 15-18gm range.

FWIW, resonance tests using the HFN&RR test record and my TriPlanar (~11g eff. mass) put a ZYX's vertical and horizontal compliance in the "desirable" 10-11Hz range - as expected. A 22-30cu cartridge on this arm resonates at higher frequencies.

Note: all this is with ZYX's that had the optional "SB" weight. A ZYX without that weight would only be optimal on a fairly massy tonearm, say 20gm or above.

Moerch recommends their heaviest armwand (the Blue, effective mass of 14g) with the ZYX carts.

As an aside, my do I love the Moerch's feature of swappable armwands of different mass (from 4-14g!).

I have a shelter 501 in a box, on the shelf, with all the other retired but still good audio paraphanailia I am collecting. The shelter was great, until I upgraded my phono stage. A couple xmas's ago I gifted myself a fosgat(from santa). The next morning I hooked it up, turned it on, cued up Hungarian dances....anticipation became lunch bag let down:(.
Instead of giving up on the well regarded fossgate, I bought a nice used zyxs airy 3( right here). After installing I repeated above process...and was happily blown away.
Sadly I don't know the r100. But I am planning to have santa bring a new airy 3 this year:).

If you've been really good, ask for a 4D. Love mine.