How important is the tonearm?

A question worth to think about, there are differences in Design (not every Arm is done perfect), the ability to guide a cartridge, to handle the resonances coming from the cartridge, the quality of the internal cable, the quality of the bearing, the material from the Armtube (wood, composite, Aluminum ...).

The better your System is (has nothing to do with price) the more you will hear the differences. The main problem is the table (and the connected electronics). Most are nothing special in vibration control and based on this, most think, the cartridge or the Arm has to be replaced when they don't "like" something in the listening..
Next is the Phonostage, most can only do 100 Ω because that is easy to design and with such a damping the higher frequencies are dead anyway.

When you have absolutely no idea from anything, go for a Graham Phantom Arm, it is clever made, works with very much cartridges on a superior level and you can concentrate the later upgrade bugs to other objects.

When I upgraded tonearm from Rega RB250 to Kuzma Stogi Reference I heard a substantial sound improvement. When I replaced Benz ACE H with Benz LP the same happened. Now I am waiting Benz Lukaschek PP-1 to replace Pro-ject Phono Box SE II. I am expecting sound improvement again.

I don't disagree at all that it is the cartridge that is the main focus in getting the music from the grooves. In the context of this thread, however, the device that is responsible for allowing the cartridge to work the best it possibly can is the arm. I have never seen or heard a cartridge work without an arm of some sort. (Those little VW microbus toys don't count!)

Obvisouly, we're leaving out every other link in the chain from cart to speaker, but why cloud the issue when the question here is about the arm.

I prefer the Triplanar to Graham because of the PITA of adjusting the damping fluid on a Graham to get it to sound it's best. The Triplanar is much easier and faster to get set, i.e. it is more user friendly IMO. Still, Graham arms are excellent. The Talea outperforms both of these right out of the box, is the easiest of all three to setup, and will allow one to really hear what a cartridge can do.

SME?!?! Give me a break.

With respect and deference to all the learned responses above, I think it's safe to say that, like everything else in our hobby, ultimately it is synergy that will yield the best results.

A top-shelf arm with a low end cart or a low-end arm paired with a top-shelf cart will both probably be bettered by a mid-grade arm and a mid-grade cart whose mass and compliance are optimally mated.

So neither the arm nor the cart can claim top billing!

Deare Acadie: For many years I " supported " that the tonearm and cartridge are one and only one audio item not two audio items.

The in between relationship is so critical on quality performance level that made a hard " task " try to separate one each other.

Yes, there are different build quality level tonearms and differences on " user/cartridge friendly " set up level in its design.

I think it is easy to hear the difference between and expensive tonearm vs a cheaper Jelco if the cartridge is a wrong/bad match with the cheaper tonearm but if the cartridge makes a good match with this tonearm then it is not so easy to heard/hear differences.

I like Benz Micro cartridges that I own and I agree with Elizabeth the SME is a good option with that cartridge.

Now the Jelco is so unexpensive that if I was you I will try the SA-750E witn that Ruby 3 and if you don't like it you always could put on sale and sold it very easy.
The Jelco is a removable ( universal. ) headshell design and you could try with different buil material/weight headshells to know which one mates better with the Ruby 3. In the other side you can buy a good IC cable for the Jelco that degrade the less the cartridge signal.

All options named here are good.

Btw, I agree with Halcro: the source is the most important link in an audio chain, either digital or analog.

I posted elsewhere that the source ( any ) is the EMPEROR and all the other audio links ( including our system set up skills. ) in that system audio chain are mere subdits/slaves working in favor of the source signal trying to lose the less and adding the less ( any degradation form. ) to that source signal.

+++++ " I have never seen or heard a cartridge work without an arm of some sort. " +++++

me either, well I seen it but not heard it with out an " arm of some sort " in the same way that with out IC cables/TT/PS/speakers/etc " of some sort ", all of them are only cartridge's slaves.

IMHO as better synergy between slaves ( each to other ) and Emperor/slaves as better system quality performance.

Regards and enjoy the music,
Raul.