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-   -   Turntable design theory (http://www.diyaudio.com/forums/analogue-source/183105-turntable-design-theory.html)

SevenPointSixTwo 13th February 2011 09:07 PM

Turntable design theory
 
I want to build my own turntable, and probably a tonearm as well.

I'm in the lucky position of having my own small machine shop, and I'm reasonably skilled ( my day job is a rather specialised form of engineering )

So actually constructing a turntable isn't going to be too much of a big deal for me ( except the platter, my lathe can only accomodate an 11 inch workpiece )

What is a big deal is that I have no idea of the design methodology. Not a coherent one anyway. I have already read most of the threads here on DIY turntables ( very, very impressive work ) but I could really use a basic primer which sets out the principles I need to adhere to.

Are there any web documents I could refer to ?

Jonathan Bright 13th February 2011 09:58 PM

Not exactly sure what you mean by the term "design methodology".


Do you mean heavy Versus light platter?
Type of drive, belt, rim, direct drive?
Type of suspension or none at all etc?
Pivot or parallel tracking arm?

So when you say "principles" you do open the inevitable "can of worms" as there are different (and quite conflicting) theories about what works and what doesn't.

I mean the obvious ones are that the thing goes 'round at 33 1/3 RPM.
The minimum of spurious vibrations get transfered to the stylus......is that the sort of thing you are after? I suspect you will need to go into the whole area of mechanical vibration and how to minimize and damp them. The study of pivot geometry is pretty well understood and will be easily accessible.

Is that the sort of thing you mean?

I have some literature in the form of mag' and journal articles that may be useful later.

Look forward to your project and further thoughts.

Jonathan

SevenPointSixTwo 13th February 2011 10:31 PM

Quote:

Originally Posted by Jonathan Bright (Post 2467660)

Do you mean heavy Versus light platter?
Type of drive, belt, rim, direct drive?
Type of suspension or none at all etc?
Pivot or parallel tracking arm?

Jonathan

Yep, all of those, that's about the size of it :)

The room where I will be listening has a wooden floor and is very close to a road which has quite heavy traffic passing by - trucks, kids in 'hot' hatchbacks with noisy exhausts playing that awful drum and bass music at ten million decibels, etc etc.
So resistance to vibration from external sources would be a high priority.

Or I can always buy another house :D

vinylkid58 13th February 2011 11:35 PM

Quote:

Originally Posted by SevenPointSixTwo (Post 2467689)
The room where I will be listening has a wooden floor and is very close to a road which has quite heavy traffic passing by - trucks, kids in 'hot' hatchbacks with noisy exhausts playing that awful drum and bass music at ten million decibels, etc etc.

The boom boom cars are "the" worst. It's pretty quiet around here, so you came hear them coming a mile away.

Quote:

Originally Posted by SevenPointSixTwo (Post 2467689)
So resistance to vibration from external sources would be a high priority.

Wall shelf.

Quote:

Originally Posted by SevenPointSixTwo (Post 2467689)
Or I can always buy another house :D

Not if you have a nice shop.

jeff

Jim Leach 14th February 2011 01:35 AM

It's not easy!
 
I am doing thew same thing right now. Actually, I have been at it for about a year so far with not much 'stuff' to show for it.

I am on my third design of the tonearm and will finally begin cutting metal.:)

I thought I had a main bearing design and recently learned new (to me) information which literally turns my main bearing upside down. (scrap all those drawings!)

The more I learn, the more I need to know...:headbash:

It seems easy enough- spin the record and drag the cartridge across... Not that easy I'm afraid (if you want something more than you get from the local Wal-mart (do you have them there?))

Please become a member of www.vinylengine.com and do a TON of reading there. Lots of great information, and people with so much knowledge and experience with turntables is is rather scary.:eek:

Final bit of advice: Linear tracking provides the lowest possible tracking distortion. The down side is that it is so difficult to implement that you will have distortion from other sources that eclipse the distortion you would have from a 9 inch arm. (longer 'normal' arms have lower tracking distortion).

Good luck!

Jonathan Bright 14th February 2011 02:32 AM

Okay 7.62 (if I may) that is helpful. Like JIM my first thoughts were vinylengine. I'll do some digging around here and see what I can dig up.

Again as Jim says wall mounting is an option but you can pursue another option that a DIYer can attempt but which is "unsellerable" commercially and that is to go for a very high Q sprung plinth.
Get back to you with some reading in a day or so. I have a good design for a diy linear tracking arm that you'll love making.....ho ho

Jonathan.

limono 14th February 2011 03:53 AM

I say forget about it and since you seem like a reasonably skilled and paid professional just go around, listen to few designs and buy the one you like. It will be way cheaper and less frustrating than trying to build good sounding TT. My friend recently built a copy of commercial table thinking that aluminum is aluminum and bearing is bearing and no way he is paying the price they ask for those TT's. His table sounds OK ,but not quite as good , actually a miles behind the original TT (which is not as pretty like DIY clone).He probably would be happy with it if he didnt have a chance to compare it directly to original unit . This is what happens here all the time with various DIY attempts I guess. I do not say it can't be done it just not going to happen after one attempt. . Best of luck!
(I need it too, as I am also building one based on various ideas but the project started years ago and I want to finish no matter the outcome;)

benb 14th February 2011 04:14 AM

I see isolation as less of a turntable issue than a platform issue. IMHO, this google search link provides much good research on the topic. I'd go with the inner tube isolation AND the wall shelf.

benb 14th February 2011 04:55 AM

I read through the following thread a while back when I first started on DIYaudio, it makes for interesting reading as far as comparing direct drive and belt drive:
http://www.diyaudio.com/forums/analo...hy-dd-bad.html

Depending on what material you want to make a platter from, this webpage on making wooden (!) wheels for a bandsaw (!) may be instructive:
Bandsaw wheels

Jonathan Bright 14th February 2011 05:47 AM

Hi 7.62, as you can see from the replies there is a mixture of frustration and admiration at your intentions. True, you have not picked an easy task but, what the hell, there is some satisfaction from diyourself. I know what limono means but on the other hand things we build ourselves ALWAYS SOUND BETTER no matter what the objective evidence indicates...ha ha.

Okay. Just to get started on some of the design compromises. Heavy platters have high inertia and so it is harder to make them change speed. So they are less suceptible to being slowed by extraneous influences...........on the other had they take proportionally longer to get back to the right speed! It is the converse for lighter platter. (BTW 11" is not the end of the world. You can get round that at a later date.)

Arms. I will dig up the parallel tracking arm design simply as you may be attracted to the machining involved. Now pivoting arms are correctly aligned at only a few points (two, I think) as they sweep across the record and just slightly out for the rest. In theory P/trackers are perfect across the whole disc.......except that idea assumes that the diamond is aligned properly in the cantilever when the cartridge was made (if an an elliptical stylus, of course). Other wise if the axis of the diamond is out when assembled then the P/tracker is out by the same number of degrees over the whole distance!!! Now you can get around this problem with a decent test record and presetting the necessary compensating error correction into the headshell/arm connection. That is pretty simple.

I admire your intentions and don't want to discourage you but there is some work both in theory and practice ahead....

BTW what part of the UK are you in? I was from Bristol originally.

Cheers,
Jonathan


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