So when designing a tonearm...

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I have read some stuff on tonearms, various builds etc. I plan to make a unipivot, but don't see too many measurements i can borrow from so had a question or six....

Does the pivot to stylus distance have to be predetermined and set in stone? I intend to work angle into my headshell, and am shooting for about 12". How far back past the pivot should the counterweight end go? Shorter the better or? Or are we shooting for a certain weight to the weight and that determines stub length? Thanks
 
I just got an SL QL5 up and running for a friend the other day. So nice.

I guess the things I am worried about are of little consequence, because once the arm is built, I can then design a protractor to align the cartridge? I am looking at the Rats Paw DIY tonearm on AudioKarma, and I think I am going to contact him and get some questions. Thanks
 
Hi morton,
You can use any practical length and calculate other dimensions. Below is a link for Excel spreadsheet calculator
Free Cartridge Protractor And Speed Discs!

I believe that shorter counterweight distance and heavy weight (lead) is better.
Marek
 

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The effect of counterweight mass on inertia is usually overestimated; doubling the CW mass and halving the stub length will generally only reduce inertia by around 10%.

A more practical reason for going the short stub / heavy CW route is to reduce the real estate required for the rear end of the arm.

It has its drawbacks, for instance it increases bearing reaction force and therefore friction.
 
Hi everybody,

Why are we looking for low inertia?
Are we talking about whole tonearm inertia or cartridge inertia?

I am building a high mass unipivot (see "man on wire" thread) because I wanted a good tracking of the grooves, which causes a very slow lateral motion, but I seek for high inertia of the cartridge in order that the stylus senses and reacts better to the micro-accidents of the groove.
Am I completelly wrong here??? :confused:

Thank you,
M
Analog débutant.
 
If the center hole is exactly on center and there are no warps, the mass becomes a non-issue but in the real world those things are not guaranteed so low mass/inertia helps. However low you manage to make the arm mass, it's orders of magnitude greater than the stylus assembly.

 
The inertia to move the arm across the record is felt by the stylus, as the stylus suspension wears or dries up in the case of Audio Technicas' small rubber O ring the inertia creates record wear. Force times distance is the amount of weight you bring to bear when tightening a nut and bolt, so if you imagine removing your car wheel nuts with a small hand spanner against a socket set with extension arm you can see that less inertia is required with a long extension arm than a small spanner. Apply this back to your arm/cartridge and the longer arm requires less force from the stylus to move the arm across the record.
 
Once the static inertia (or moment of inertia) is overcome in the first revolution then there is dynamic inertia related to the rotational velocity of the arm that is present. As the rotational velocity of the arm increases ever so slightly with each subsequent revolution the inertia of the rotating arm builds. I would definitely like to see some experimental data that show these almost infinitesimal changes in inertia related to rotational velocity actually cause any audible distortion. It occurs to me that the rolling friction of the gimbal bearings is more important that the moment of inertia of the tonearm.

John
 
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I have Made, and Listened to this style Nanook Arm...And, it's really the Most Satisfying and Great Sounding Uni-Pivot DIY Arm that you can do without a Shop...I am Planning on making another, with a Carbon Arrow Shaft...So, I removed the Out-Riggers to see if they where Needed...And Yes, They Are...It will Wobble on the Vert. as soon as you Lift It...I put Them back On...And, I can Lift It, and Drop It into the Groove with No Vert. Wobble..
300694d1347279400-man-wire-unipivot-tonearm-debbie-tone-arm.jpg
 
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