tonearm cable, do you need one?

Not unless there is something wrong with what you're currently using. If you do require a new cable and want the best quality - search ebay and other sites for "made in Japan." 

Some IC's may be noisier than others due to build(shielding) If you choose to not use phono   cables, just use a piece of wire  for the ground(table to phonostage). You may not even need it. My VPI doesn't depending on cart used for whatever reason.

Zu Audio Phono cables with ground wire are excellent!
You need shielded phono cable.
Read more here.

And on ebay you can find their auctions for Mission Phono RCA cables with starting price at $1, normally goes for $80-100 on those auctions. They are great for the money! 

If your phono cable does not have this third ground wire then you can still try it, and if you hear some hum then you can’t use it without separate ground wire, just try it.

You do need a cable that is specific.

The reason is capacitance, something that occurs with any interconnect cable. With a phono cartridge, which has inductance, the capacitance will form an electrical resonance. If its a high output cartridge this might be at or just above the audio passband.

If you don't have a low capacitance cable, the resonance will be in the audio band with that high output cartridge. It will sound peaky and bright. So you need a low capacitance cable, nor more than about 20picofarads per foot. The ground wire is there to prevent buzz from being audible. It is connected to the ground of the arm itself and the chassis of the phono preamp.

+1 what @chakster  said.

Also you have shielded IC's you can run a  separate ground wire using an inexpensive 16-18ga wire

Easy peasy ADD a ground wire. From the source to the phono stage and the phono stage to the preamp... No phono stage! Go from the source to the preamp.. I use good copper... 1.00 usd.. for the GREAT stuff...

NOISE... connect it..

Regards

Thanks Ralph @atmasphere . I think I may have known that but its been a long time since I had an arm without the captive cable. Its good to be reminded of error. But don’t tell my wife I said that. (-:

The VPI cables are made using the same Discovery wiring that the VPI arms are wired with, that is unless it is the upgraded arms with the Valhalla wiring. There are those who believe as I do that the combination would have a given synergy. Enjoy the music

I don't need one, I have 3.

"I don’t need one, I have 3."
How special! What does that have to do with the question that was asked from the OP? Nothing!

Low capacitance, screened, relative flexible and not too heavy.
For ground you can use any piece of wire made from good copper.
You may benefit by using the same kind of wire, silver or copper, that is in the arm tube.

G

@petg60 he’s asking about RCA to RCA type, his TT has RCA output with ground pin.

Thanks chakster, i know, but i suspect that same would apply for rca to rca. Relative flexible and not too heavy would  have less stored energy and be easier to route. 

G

I use a VPI phono cable with my Classic 1 which is an extension of what the arm is wired with good system synergy.

I did end up getting a couple phono cables.  The VPI phono cable and also an Audio Envy phono cable.  I like the Audio Envy better all around. The VPI is a little thinner and brighter, it's close but I'm keeping the audio envy.  I don't notice anything different with or without the ground attached so maybe you can just use an interconnect and don't need the specialized phono cable.  

The difference between phono cable and interconnect cable is SHIELD , not a ground wire. Do you understand why 99% phono cables are shielded? The signal from phono cartridge (especially MC) is much lower than line level signal from any other component. Without shielded cable you can hear a radio signal in your speakers or noise and hum when you connect it to your tonearm/turntable with MC cart.
Some interconnects are shielded, but most if them are not shielded and using them instead of phono cable is bad idea.

As for the ground wire you can use any thin wire (it will not affect sound quality) between turntable ground terminal and phonostage ground terminal if needed.