How critical is the exact placement of the tonearm

Hello All,
There is a minefield of information on this thread for newbies. It does explain however, that when I put a different type of allignment tool on my Rega P3 many years ago, I couldn't get the geomtry right.

Anyhow, that arc protractor sounds helpful. Does anyone have a link for that Gent in Hong Kong who makes one for under $100?

Also, where does that old Mobile Fidelity alignment disc (the one that was the size and shape of an LP) fit into all this? Is the Mobile Fidelity disc Baerwald geometry? Is that disc an accurate enough tool to use in the correct alignment of arm and cartridge?

Hi Rene,

You didn't miss anything. You are correct that there is no preferred effective length (as long as you are not using an arc style protractor which is drawn for one and only one set of parameters).

The benefit of a two point protractor is that with enough diligence, flexibility in the headshell slots, etc. you can get a perfect alignment irrespective of your pivot to spindle distance being off - as long as you have enough movement in the headshell slots to adjust the effective length and offset angle to match your "wrong" pivot to spindle distance.

With an arc style protractor, the price you pay for ease of visualizing and solving the problem is that the pivot to spindle distance must be very close to perfect, because the arc is drawn from the theoretically correct arm mounting (pivot) point.

Dsa - A few posts up, I have a link to an arc protractor thread. In that thread, Richard posted a link to the protractor fellow. He loves it even more than his "original" arc protractor.

Cheers,
Thom

Hong kong guy Arc protractor link http://www.mintlp.com

Very easy to deal with, fast turn-around. Not sure I've got the alignment right yet; its pretty tough when you wear progressives and are really far-sighted, but it appears to be well made and the instructions are not bad.

Hi Swampwalker- thanks for the link. Looking at the info on their site- the customer sends their tonearm and turntable brands (and also cartridge?) and they make a tractor specifically for that set-up?

That's correct, Dsa. The proprietor, Yip, makes the protractor for the tonearm parameters you specify. I had given him the numbers for the protractor I need without the name of the tonearm and table. I guess he is building a database as he asked for these before accepting my order. Another thing that came out in the thread on Thom's forum is that you will also need to specify the spindle hole diameter. Yip does cut to high tolerances so keep that in mind with the spindle hole. Oh, I also like the way he personalizes them.

Yip also asked if I wanted a lupe he recommends for seeing what is going on while adjusting with his protractor. I ordered one since I liked the look of it and feel I can never have too many tools for seeing what I'm doing.

What I like about the arc-style protractor is that you have a single tool that allows you to get the pivot to spindle right at the same time you get the cartridge alignment right. It is possible to get things right with most any 2 point protractor, but you would still need a tool and method to measure the pivot to spindle to get it really, really close. So if you are getting accurate results with a 2 pointer, that's all you need. In my case, I didn't realize how off I was until I tried the arc-style. I was clearly off the arc. Once I got things adjusted closer and re-checked using my 2 pointer, I found I was off by less than .5 mm with pivot to spindle. But the difference in the sound of reproduced music was noticeable, especially in the articulation of consonances. Well, that's what I noticed first. I suppose the benefit is to all micro-dynamics. Getting this adjustment closer to theoretical perfection provides for just that much more of an "in the room" presence from practically every LP I played since. There is probably still a small error in my setup but I'd say it is limited to the width of the printed arc. Once Yip's protractor arrives I'll adjust things again.