[digitalmind]

What/why?

My latest project, my speakers, is nearly completed (ha! who am I kidding?), so I'm on the lookout for something new. Thanks to Dexdexter, I have a Rega Planar 3 sitting here.
It's not complete at the moment (no cartridge or tonearm cable). I ordered a Denon DL-103 and am still looking for a nice DIN to RCA cable for the tonearm. If I can't find one here locally, I'll grab one on eBay where there are multiple affordable nice ones.

While the P3 is a classic, it's far from optimal. The motor isn't suspended and is close to the platter and to the cartridge/arm. The dampening isn't very good. It's currently sporting a Linn Basik LVX arm, a decent starters tonearm but also not a very high end arm. Still, it's what I plan to use for some time to come, though I'll most likely move up to a Rega 300B (or something in that league) in the somewhat near future. An overall decent table, but not the best...

Ok, so why in the DIY section? Simple: I'm going to build a new turntable with the P3 as a source for parts and am keeping a log here. This isn't a project that'll move along very quickly, so don't expect daily updates though.

A turntable is a relatively simple machine and, unlike speakers, can generally be designed by anyone.

Goals

I have two goals: to get the best possible sound quality from as little money as possible, and for it to look like a product that could be bought in a store. Completely opposite of my speakers, I'm going for a 'proffesional' look with nice finishing.

Parts

I'm sourcing my parts from the P3. I'll be using the motor, bearing, platter and tonearm from the P3. Will be using a Denon DL-103 MC cartridge, and still have to find the tonearm cable. I might move on to a different tonearm at a later stage, but for now, the Linn Basik will have to do.

Ideas

High frequency vibration is bad. With that in mind, there are a couple things I want to do.

1. Get the motor further away from the platter and tonearm. Get the platter and tonearm on a seperate part. I'm not sure if I'm going with a single belt to the platter or two with a second subplatter in between.

2. I'm going to have the part with the platter and tonearm (let's call this the Table) seperate from the part with the motor (let's call this the Base), and will have the Table suspended on elastics in the Base. The Base will be made as heavy as possible without going too far and hindering possible transport. The Base will be filled with sand for vibration dampening.

3. Keep the possibility open for tonearm relocation to the Base.

4. The entire thing will be placed on feet, possibly rubber.

5. The Table will essentially be a better built clone of the P3 without the motor. It will have the same dimensions.

6. Material will be 18mm MDF. Every part used is two 18mm plates on top of eachother, possibly milled out in the middle and filled with leadshot.

7. While parts are seperated, I still want it to be a one-piece unit.

How?

I've doodled this up in Sketchup last night.
You can see the suspended table hanging 'in' the base, and the base filled with sand for weight/vibration control.

This render isn't entirely accurate to my ideas. The Table will come to rest on elastics that span from one side of the Base to the other. It won't be attached to them like in the render, the elastics will go under the Table.

Comments, tips, help, ideas, everything is highly welcome! Like I said, this won't be a project that'll move along very quickly, but there should be updates here from time to time.

Thanks for looking!
Rik

 

[xnothingpoetic]

Why not magnetically suspend it?

 

[digitalmind]

Quote:

Originally Posted by xnothingpoetic /img/forum/go_quote.gif Why not magnetically suspend it?

I figured this would be very hard to get right, and magnets aren't cheap, so I quickly dismissed it. The added weight of the LP itself and the puck may prove troublesome for the balance. Then there's the motor belt pulling it one way.

If I can find a cheap source for some small and strong magnets, that might be a very cool idea indeed to play around with though...

 

[Bjornboy81]

MAGCRAFT® Neodymium Magnets

They have all different sizes with different pulling forces...not badly priced either! Cool idea

 

[InSides]

Ah! You couldn't wait just a tiny bit! And now I look at my Debut III all alone in the corner, thinking what I could do with it's bearing, motor and platter.

OK, just a few thoughts, then.

Have you set your mind on a suspended design? Since you already have all th necessary parts, why not go the massloaded design and put the bearing, subplatter, platter in a sandwich mass loaded plinth [MDF, ply, MDF], and the AC motor in a standalone smaller base cosmetically matched to the main plinth - think Walker Proscenium turntable.

That way, the tonearm will be isolated from the table, and it should be fairly simple to execute. Not to mention that you have a much larger chance to achieve a professional looking finish.

Also, a good point are interchangeable tonearm bases. Just in case.

Oh, and since it is a AC motor, and this is a DIY effort, maybe throw in a AC motor controller, such as the kit offered by Mark Kelly?

And finally [and I know I've already told you this

] you might want to look into the Jelco line of tonearms, specifically the 250 and the 750. The lesser can be had for ~$270, and it comes with a detachable headshell for when the cartridge madness strikes.

Ah, now to see how to dismantle that Debut bearing...

 

[digitalmind]

Quote:

Originally Posted by Bjornboy81 /img/forum/go_quote.gif MAGCRAFT® Neodymium Magnets They have all different sizes with different pulling forces...not badly priced either! Cool idea

Hmm, that's not expensive at all.

Perhaps, instead of having the whole Table floating, it'd be an idea to only have the platter float? Multiple magnets on the underside of the platter and on the Table, it should be possible to support the weight of the platter and puck. How would I keep it centered? Using multiple Arc-Segment magnets? The Cylinder and Ring magnets unfortunatly don't have their poles on the in- and outside.

 

[digitalmind]

Quote:

Originally Posted by InSides /img/forum/go_quote.gif Ah! You couldn't wait just a tiny bit! And now I look at my Debut III all alone in the corner, thinking what I could do with it's bearing, motor and platter.

Strip it and play with it!

Quote:

Originally Posted by InSides /img/forum/go_quote.gif OK, just a few thoughts, then. Have you set your mind on a suspended design? Since you already have all th necessary parts, why not go the massloaded design and put the bearing, subplatter, platter in a sandwich mass loaded plinth [MDF, ply, MDF], and the AC motor in a standalone smaller base cosmetically matched to the main plinth - think Walker Proscenium turntable.

Also possible, but I like the idea of a single unit more than two seperate parts. I know, suspending the table is hardly 'single unit', but still. It is something I'm thinking about pursuing rather than the suspended design though, and you shouldn't be surprised if I end up going that route.

Quote:

Originally Posted by InSides /img/forum/go_quote.gif That way, the tonearm will be isolated from the table, and it should be fairly simple to execute. Not to mention that you have a much larger chance to achieve a professional looking finish.

In what way is the tonearm isolated from the table? Through the mass-loading?

Quote:

Originally Posted by InSides /img/forum/go_quote.gif Also, a good point are interchangeable tonearm bases. Just in case.

A very good idea, since I'll most likely swap tonearms later on. Will probaby execute this in much the same way as I have the swappable driver baffles in my speaker.

Quote:

Originally Posted by InSides /img/forum/go_quote.gif Oh, and since it is a AC motor, and this is a DIY effort, maybe throw in a AC motor controller, such as the kit offered by Mark Kelly?

Maybe, but my last turntable was electronically switchable, but I never used it. 33rpm will do me fine, and with the motor out from under the platter, switching speeds manually isn't much work. Or are there other upsides of such a motor controller?

Quote:

Originally Posted by InSides /img/forum/go_quote.gif And finally [and I know I've already told you this ] you might want to look into the Jelco line of tonearms, specifically the 250 and the 750. The lesser can be had for ~$270, and it comes with a detachable headshell for when the cartridge madness strikes. Ah, now to see how to dismantle that Debut bearing...

I know, and I will most likely move up to a better tonearm somewhere along the way, but it's not in the cards for now. The recommendations are most welcome though.

About that bearing....

Always works for me.

 

[InSides]

Quote:

Originally Posted by digitalmind /img/forum/go_quote.gif In what way is the tonearm isolated from the table? Through the mass-loading?

Apologies, when I said table, I actually meant the motor.

One true way to isolate the tonearm is to locate the tonearm base on a subchassis, and the motor and bearing on the chassis. Or the other way around.

There are I believe pros/cons to either approach, as some designers prefer to have all the 'vibrating' elements of the turntable on a single plane.

I have been thinking about a split design for some time now... I have been looking into the Scheu offered 80mm acryllic platter and main bearing, and with a combination of hard wood plinths, I might be able to achieve that true separation.

Of course, with that platter/bearing I will have exceeded what I paid for my RPM9.1, and that one comes with a tonearm.

But a guy can dream. I might finish that drawing today for my idea, and if you don't mind, Rik, I will post a photo in the thread.

Quote:

Originally Posted by digitalmind /img/forum/go_quote.gif Maybe, but my last turntable was electronically switchable, but I never used it. 33rpm will do me fine, and with the motor out from under the platter, switching speeds manually isn't much work. Or are there other upsides of such a motor controller?

AC turntable motors depend on the mains frequency to control their speed. To sustain true 33.33 operation though, one needs to control the frequency of the AC, as it will usually vary, bringing speed variations in the level of +/-5%.

What the Speed Box did for your ProJect, and what an AC motor controller will do is make sure that the turntable motor produces the _exact_ AC frequency to keep the motor spinning at the precise 33.33 RPM.

 

[digitalmind]

Quote:

Originally Posted by InSides /img/forum/go_quote.gif Apologies, when I said table, I actually meant the motor. One true way to isolate the tonearm is to locate the tonearm base on a subchassis, and the motor and bearing on the chassis. Or the other way around. There are I believe pros/cons to either approach, as some designers prefer to have all the 'vibrating' elements of the turntable on a single plane.

Most "high end" units have a seperated motor though.
Suppose the tonearm is on the same chassis as the platter, would it be a nice idea to seperate the two parts and reattach them with bolts and rubber o-rings in between?
All this might be going slightly over the top... but that would be very easy to do and can't be a bad thing.

Quote:

Originally Posted by InSides /img/forum/go_quote.gif I have been thinking about a split design for some time now... I have been looking into the Scheu offered 80mm acryllic platter and main bearing, and with a combination of hard wood plinths, I might be able to achieve that true separation. Of course, with that platter/bearing I will have exceeded what I paid for my RPM9.1, and that one comes with a tonearm. But a guy can dream. I might finish that drawing today for my idea, and if you don't mind, Rik, I will post a photo in the thread.

Sure, I'd like to see it! This thread might as well be a more general thread about the design and build of DIY turntables.

Quote:

Originally Posted by InSides /img/forum/go_quote.gif AC turntable motors depend on the mains frequency to control their speed. To sustain true 33.33 operation though, one needs to control the frequency of the AC, as it will usually vary, bringing speed variations in the level of +/-5%. What the Speed Box did for your ProJect, and what an AC motor controller will do is make sure that the turntable motor produces the _exact_ AC frequency to keep the motor spinning at the precise 33.33 RPM.

I would have figured there to be a small ac-frequency regulator in the Rega. If not, then the motor controller is pretty much a must... Though I'll check it out with a stroboscope to see how well the P3 keeps up to speed.

 

[Bjornboy81]

Quote:

Originally Posted by digitalmind /img/forum/go_quote.gif Hmm, that's not expensive at all. Perhaps, instead of having the whole Table floating, it'd be an idea to only have the platter float? Multiple magnets on the underside of the platter and on the Table, it should be possible to support the weight of the platter and puck. How would I keep it centered? Using multiple Arc-Segment magnets? The Cylinder and Ring magnets unfortunatly don't have their poles on the in- and outside.

I would have the whole table float just so that there's more mass and it would be less suseptible to vibrations from the motor/belt. Too little weight and any vibration will be transmitted, even through the belt. One magnet in all four corners' bottom, and two vertical sides would be plenty to stabilize it.

 

[InSides]

OK, here goes the preliminary design...

...named Rik's TT, just to remember who helped towards yet another wallet killer. The sketches are pretty rough. I do admit some packages like SolidWorks create more life-like images, but I like the simplicity of wireframe, so please bear with me on this.

Overal idea is two separate plinths, coupled together via massive brass spikes. The lower plinth houses a variation of a massive bearing design and the 320mm / 90mm Scheu platter. The upper plinth has a 330mm opening for the upper part of the platter and houses the interchangeable tonearm bases.

The motor reside in a separate enclosure mimicing the main plinths. Reason for dual plinths here as well is the possible usage of dual AC motors with a central flywheel. Just a thought.

With the motors separate from the plinth and the arm boards on a separate plinth that the bearing/platter reside on, the tonearm should be effectively shielded from motor/bearing/platter vibration. Whether that is a good thing, I can only tell you when [and if] I ever have this thing built.

Here is a wireframe overview to get a look at the location of the platter, bearing, separate motor base and coupled plinths:

And here is the rendered view:

Note the motors are not drawn yet

as well as the armboards. If I decide to pursue this design [who am I kidding, I know I will, this is yet another distraction] those will come in a day or two.

Here is the wireframe view from the front - the bearing/platter/coupler relations can be seen:

And here is the rendered view:

Enough for now - I should really get back to work.

 

[HiGHFLYiN9]

Very cool renders Insides, that's going to be gorgeous when you're done with it.

I'd personally avoid the magnets as I would think they would have a chance to screw with the cartridge if they are strong enough.

 

[InSides]

Thanks... although I am again regretting not being able to locate a proper machine shop to execute this. And even if I did, who knows how much they would charge. Ah well...

Also, one potential problem with using the Scheu platter/bearing is that the 320mm diameter makes it difficult to properly mount 9" tonearms, so I might need to go with something like the Pro-Ject 10cc or some 12" variant.

But I will stop derailing Rik's thread - I promise to come back with some designs to reuse the P3 bearing/platter.

 

[digitalmind]

Quote:

Originally Posted by InSides /img/forum/go_quote.gif Thanks... although I am again regretting not being able to locate a proper machine shop to execute this. And even if I did, who knows how much they would charge. Ah well... Also, one potential problem with using the Scheu platter/bearing is that the 320mm diameter makes it difficult to properly mount 9" tonearms, so I might need to go with something like the Pro-Ject 10cc or some 12" variant. But I will stop derailing Rik's thread - I promise to come back with some designs to reuse the P3 bearing/platter.

Actually -- your design has inspired me quite a bit. I can try something with a different platter. Not derailing the topic at all, great stuff. Back to the drawing board...

 

[amb]

It is absolutely imperative that the tone arm and the platter/bearing assembly be fixed to the same base, and rigidly coupled. The geometry between the two must be relatively fixed in order for the cartridge to be aligned to "read" the record correctly.

Imagine what happens it it isn't... if you were the cartridge and the tone arm is a boat floating in the ocean, and the platter is a mass of land off the distance somewhere!