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jrubins 13th November 2009 04:38 PM

Building my own TT need some advice
 
3 Attachment(s)
Hi all,
I've been into DIYaudio for a while, but new to these forums.

I've been doing some reading online (esp in these forums) and I'm ready to try to tackle a turntable build.

My main questions have to do with tonearm design:
I'm trying to build a (loose) copy of the well tempered design.

My questions are:
How far away (spindle to pivot) must the arm be mounted for a 10.5" armtube? Does it actually matter?

Antiskating: does it need more or less towards the center of the record?




I've seen a few discussions on bearing design, and I'm including mine here, for reference and discussion.

The main break with tradition I'm considering is the inclusion of a plastic bearing sleeve. The plastic would probably be delrin or ptfe or some combination thereof.
Probably something like this one
McMaster-Carr

The platter and plinth will probably be 3/4 plywood, although mdf is a possibility, and I *may* be able to make the platter out of acrylic or lexan.


The only other thing of note about this TT is a separate armboard. I think physically separating the armboard from the motor *and* the bearing should decrease noise even further, although it could complicate setup.

Anyhoo, thanks for your thoughts.
James

jrubins 15th November 2009 07:14 PM

Anybody?
Bueller?
Buuueellllllleerr????

Steerpike 15th November 2009 09:19 PM

Quote:

Originally Posted by jrubins (Post 1979556)
How far away (spindle to pivot) must the arm be mounted for a 10.5" armtube? Does it actually matter?

It DOES matter. But it depends on the chosen offset angle, the chosen overhang, and what method you choose for minimising tracking distortion (i.e., where you decide to place the so-called null points.)

If you are cloning an existing design, easiest to consult the documentation for that one to find the arm pivot position.
If you are making it entirely to your own design, you'll have to calculate it from the rules of geometry.

Jeffrey Davison 15th November 2009 11:53 PM

check this out.....

There is an Excel spreadsheet that may interest you, it's very useful

go to the bottom of the page....you can plug in your desired effective length of the tonearm and the spread sheet will compute the pivot to spindle distance, offset angle of the cartridge etc.... it will give you a graph of distortion and you can use either the Lofgren A (Baerwald) or Lofgren B calcs...


Free Stuff

Studio Au 16th November 2009 12:49 AM

Always a good place to start:

The Altmann DIY Tonearm

If you wanna get a little better:

JoŽl Durand - Unipivot project

The above link 'free stuff' the protractor was fantastically useful.

The schematics for SME tonearms and such are easily available, most probably worth cloning.

As far as bearing goes, unless you have an incredibly accurate machine shop, it is far more practical, and less expensive to buy one new or old. Lenco ones for $20, new technics 1210's for about the same, or buy a Teres one if you want exceptionally good quality.

I made my tonearm from a 12" piece of wood, could be maple. I used a bronze U shaped bolt as counterweight. One end screwed into the tonarm, the other hangs below. This allows quite precise tweaking of the weighting in all directions. Supported on solid copper speaker spike (eBay) and has a 50mm diameter 40mm high 1.4kg solid bronze base.

My Platter is a 30cm Gumtree solid wood engrain chopping board. It is beautiful, heavy, has large amount of inertia (and requires a little spin to get it going as the belt is single loop of thread) also seems very inert. And at 15gbp far cheaper than most other options, next step will be drilling and filling with lead shot.

I have changed the base to a 1" thick piece of acrylic and so it all needs to be re-assembled, but when i tested it, it did sound rather fantastic.

kevinkr 16th November 2009 01:06 AM

Bearings can be a major problem. I am currently building a TT, based on a custom machined 1.75" thick acrylic plinth that I designed, a good Thorens TD-125 bearing and sub-platter/platter which I scored on eBay. There are a lot of guys on eBay also selling replacement TD-124 main bearings - with the right spindle it is hard to imagine doing much better than this other than the Teres set up which I suspect is a lot more expensive.

I had Allied import a TT specific Premotec motor from Holland for my table. A friend made the custom two step pulley. The motor will live in a small pod which I am still in the process of getting together. THe pod is completely independent of the plinth, but lives between the sub-platter ring and the outer ring of the main platter.

I wimped out on the arm - I had originally thought to clone the Hadcock HA-228 arm but ended up buying a Rega RB301 instead.

This table does not have a floating suspension but will be isolated to some degree from the heavy shelving system it will be installed on by 3 supporting points which I will have to evolve based on experience.

How about some details on the plinth, motor, bearing. I'll post some of my stuff as an inspiration if you would like - still have to snap some pix.

john65b 16th November 2009 01:31 AM

I have an old, still working B&O 1800 I was thinking of gutting and reusing the platter, and motor. I will not be using the arm that requires the MMC type B&O cartridges that are obscenely expensive...which is the real reason I was thinking of building a TT in the first place.

Still have my B&O TX2 Tangential with MMC3 cartridge as a backup. Not a horrible TT BTW...

jrubins 18th November 2009 05:25 PM

Thanks for the advice gang!
here's what I have so far.
Note: pics are Facebook hosted, so if you can't see them, I'll move them to flickr or some other ridiculously named online app :)

http://photos-c.ak.fbcdn.net/hphotos..._7013153_n.jpg



http://photos-h.ak.fbcdn.net/hphotos..._6937260_n.jpg

http://photos-h.ak.fbcdn.net/hphotos..._6937260_n.jpg


The armtube is a carbon fiber arrow shaft. Headshell is a piece of balsa, as is the bit that attaches the tube to the golf ball.
The golf ball bearing is a take off of the well tempered design.
The bearing itself will be fishing line attached to the two screws in the golf ball.

Once I've got the geometry figured out, I'll attach a counterweight and cartridge (somehow :) )

jrubins 20th November 2009 05:53 AM

Ok gang, I've got the tonearm working :)
http://photos-a.ak.fbcdn.net/hphotos..._1534252_n.jpg

http://photos-h.ak.fbcdn.net/hphotos..._7265252_n.jpg

http://photos-f.ak.fbcdn.net/hphotos..._4394769_n.jpg

http://photos-b.ak.fbcdn.net/hphotos..._4170927_n.jpg

I'm too tired to go into all the details, so I'll post some in AM.

'night all

jrubins 25th November 2009 12:08 AM

So, I've been using this DIY arm for a couple days now...
Thus far the impressions have been very positive.
Despite sitting on a stack of slippery cds, which necessitates a realignment every session. :sigh: The sound is very good.
There is a lot more bass than with the stock Pro-Ject arm.
The bass also seems tighter and more focused.

At first I thought this extra low-end might be a result of improper VTA, but after raising and lowering the VTA (hence the Cds) I feel that it's a real gain in bass performance.

The top end still sounds the same as the stock arm, which I suppose I expected. To be honest I am really blown away by the sonic improvement the arm has brought, I didn't expect the tonearm to have that large an effect.


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