tonearm parameters

I've been reviewing turntable recommendations, on this and other forums, and what I'm struck with is advice that often you should upgrade the tonearm. This is especially true of vintage Thorens, Technics ,Luxman,and many other turntables Frequently, [not exclusively] Rega tonearms are recommended. We'll, I've had Rega P3,P5,RP6, and currently, RP8 turntables as well as Music Halls and Project TTs. In addition, I've had VPI TT's. I'm at a loss as to what is optimal in Tonearm qualities, and respectfully request from Audiogon members what exactly are the paramaters to look for.
Choose an arm that is appropriate for your cartridge. Low mass cartridge should be installed in a low mass arm. Choose an arm for its adjustably. All aspects of cartridge setup should be clear and easily adjusted. Good bearings and precision of manufacture will be important especially for long term performance.
That's a really open-ended question, Boofer! The answers (there are quite a few) really depend on vinyl condition, the table you're mounting the arm on, what kind of cartridge you prefer and how much adjustability you want. Oh, and your budget, too. Personally, I prefer arms that can adjust VTA on the fly; that one feature makes a huge difference to my ears simply because no two records are the same thickness. An arm designed for cartridge alignment via some sort of fixture is also a feature I prize. My eyes aren't so good anymore, and the old-school protractors are just too hard to for me to see clearly. As you know, proper alignment is the be-all and end-all of getting the most out of your rig. The third important feature to me is a unipivot bearing; the ability to track the groove at whatever odd combination of angles is necessary just seems to make a lot of sense.

Rega arms have none of those features. That does't make them bad, just different. Some of the best TT performance I ever experienced was with a Planar 2 with the original arm and a Dynavector MR23 back in the day. The current crop of Rega, Pro-Ject, Music Hall and VPI tables are all wonderful products at their various price points. With any of them, give thought to SME, Tri-Planar, Graham, Clearaudio, Ortofon and Dynavector. They all make great arms that, depending on your particular system combination, can return awesome performance. Each one has advantages and disadvantages, so make sure you read up on them, because none of them are cheap. Good luck!

Good luck!
Take a look at the Transfi-Terminator tonearm and read some of the reviews on Audiogon and AudioAsylum.
Yes, cartridge-tonearm matching is key. And the Cartridge and Tonearm Databases over on Vinyl Engine are an excellent resource for determining a good cart-tonearm match.

One tonearm maker that offers considerable versatility in this area is Moerch, which has easily swappable armwands, which are available in a number of different effective masses. It is the effective mass of the arm that needs to match up well with the cartridge's compliance. An additional advantage of Moerch's armwand system is that it becomes easier to use multiple cartridges without the structural compromises inherent in swappable headshells.

As for Rega's, they are well-thought of arms, but you will also find many upgrade kits that will improve their performance. From rewires, to structural reinforcement, to VTA on-the-fly, to upgraded bearings. I really liked my Audiomods arm, which is the most extensively modified Rega arm, IIRC. It served me very well before I moved to Moerch arms for the reasons cited above.
I MY experience, adjustment of azimuth is a vital contribution to proper vinyl playback. After you get the proper geometry for your arm length, and get proper downward force, azimuth is next in importance...though all parameters are vital.
Dear Stringreen: +++++ " Low mass cartridge should be installed in a low mass arm. " +++++++

cartridge compliance is the " key " to define low mass or high effective mass in the tonearm. Yes, cartridge weight is important but the critical parameter down there is cartridgecompliance.
Raul is correct. A statement like, "Low mass cartridge should be installed on a low mass arm" is incorrect. A better (though still simplified) statement would be, "High compliance cartridge should be installed on a low mass arm, or vice-versa".

Examples: ZYX cartridges (especially without the optional SB weight) are fairly low mass. Koetsu cartridges are fairly high mass. Put either one on a low mass arm and it will sound anemic. This is because both have relatively low compliance suspensions (for their weight). Put the same cartridges on a mid-high mass arm and they will spring to life.

To the OP: your question is so open-ended that you'll receive a confusing maze of responses. It'll be fun to watch but I'm not sure how helpful it will be. Tonearms range in cost from a few hundred dollars up to, well, you probably wouldn't believe it. Within this expanding universe the number of different theories and their execution is beyond counting. Fasten your seat belt!
I'm with Redglobe. Hard to do better for a grand or so. I would give up my SME-V before I'd let go my Terminator T-3. Adjustable in all areas from azimuth, mass, as well as VTA on the fly if you care.