What does a tonearm contribute to the sound of a turntable?


Curious about how a tonearm affects a turntable sound. I guess it's the piece of the turntable I know the least about and feel the least connection with. how does a really good tonearm affect the sound or not affect the sound? And what about the tonearm does the affecting?
128x128simao
I went from various iterations of the original SME 3009 arm to various VPI arms including two of their 3D arms to my current two arms, Reed 3P's.
I have had 9", 10.5, and 12. Steel, alloy, carbon, plastic (VPI 3D, call it "composite" if you like, it's junk IMHO), and now one Reed is 12" cocobolo and one is 10.5 in ebony.


@fsonicsmith welcome to the club, i have the same Reed 3p Cocobolo "12 :)) Wonderful modern High-End tonearm. I've met people from Reed in Vilnius, Lithuania to get my sample. It's definitely a top quality tonearm. Then i went to vintage route and it's an interesting journey with tonearms like FR-64fx and 64s, Lustere GTS-801, Technics EPA-100 MK2, Ikeda IT-345  
With the new Jelco, I now have not one, not two, but six signal interfaces between the cartridge and the speakers:
  1. cartridge to headshell/arm
  2. headshell/arm to Premiere Interface DIN (little box on the back of the VPI - which I desperately want to get rid of)
  3. Premier Interface DIN to RCA
  4. RCA to phono pre
  5. Phono pre to amp
  6. Amp to speakers
Is this normal?
Pretty much and if everything is of decent quality it should be fine, don't fret about it.
Now some will say that your losing tons of signal if your leads from the cartridge to the preamp are not one continuous lead but I say BS.
Any decent connection will have such a small loss to be unnoticeable. It takes special test gear to measure the resistance between good connectors, normal test meters won't pick it up.
So sit back and enjoy the music.
BillWojo
 It takes special test gear to measure the resistance between good connectors, normal test meters won't pick it up.
Do we have to go down that well-worn rutted road again?

@fsonicsmith welcome to the club, i have the same Reed 3p Cocobolo "12 :)) Wonderful modern High-End tonearm. I've met people from Reed in Vilnius, Lithuania to get my sample. It's definitely a top quality tonearm. Then i went to vintage route and it's an interesting journey with tonearms like FR-64fx and 64s, Lustere GTS-801, Technics EPA-100 MK2, Ikeda IT-345  

It was you Chakster who caused me to look into Reed.