Anyone "Handy" interested in a DIY Turntable Project?

I'm going for sub platter on this one. I'd post drawings up, but I don't have any as of yet! Well, I've drawn the platter but thats it!

The only qualm I have with my design atm is the platter mass will be low. I don't want to build too much peripheral mass into the platter due to the flywheel effect, which may be a problem using the Linn motor. I may well make a heavy clamp ~1.5-2kg to help dampen the entire assembly and add general mass.

Where did you get the platters from for your project? They look nice :MILD:

 

The platter's from the project comes from Pro-Ject Its the running gear off an RPM9.

How much does the Linn platter weigh? I wouldn't have thought it'd be that light. Is it about the same as a Thorens TD150 say?

Now maybe I've misunderstood, but isn't getting your platter to act like a flywheel a good thing?

 

I think allowing the platter to act like a flywheel can be very good, but only if you have the electronics to control the speed accurately.

I think that if I built a lot of peripheral mass into the platter on my projected TT design, the motor/Geddon clone wouldn't be able to keep the speed constant. I mean, if the speed was to rise, and the mass around the platter was high, the inertia may be too great for the motor to effectively 'break' the speed increase to within acceptable levels. You have to compete here with varying stylus drag amongst other things I can't think of at the moment(!).

The Geddon is after all a 'dumb' controller!

 

I would have thought that having a high mass platter especially around the edge would help the speed control of a low torque motor. Your argument works both ways, once up to the correct rpm a small fluctuation in speed caused by the Geddon would be unlikely to increase the platter speed by the very nature of the large mass, also areas of high stylus drag would not affect platter speed for the same reason. A light platter on the other hand.

 

Tony
Have you had a chance to review the plan plot of the deck yet ?

 

Hi Granville,

I have now. Looking good. We may need to sink the platter by a few mil less, I'm a bit worried the belt might snag the top plate.

Also , should there be a gap between the armboard/top plate part and the piece the bearing is attached to?

Otherwise its pretty much exactly what I was thinking.

Re the flywheel thing. I'd have thought with an AC motor and a "dumb" controller, a massy platter acting like a flywheel is exactly what you want. I can see how, if you had a DC motor and a "clever" controller which adjusted speed on the fly, you might get problems.

 

This is the space for the compliant layer, forgot to mark it in.

Do you see my point about the feet ? any futher thoughts

Bearing plate is fixed to 8mm steel plate bonded to the laminate.

I would also like to add another 8mm plate in the top half of the deck, this would give us something substantial for the arm board
block to fix into, also adding more mass to the deck.

 

Starting to sound good ....can't wait to hear it !

 

Aha. That makes sense (sorbothane sheet yes?). This would effectively mean that the top plate, arm board and arm are seperated from the platter/bearing by a compliant layer ... are there any positive or negative consequences?

Its certainly common practice that the arm/armboard/bearing/platter are part of the same piece, so to speak, but i don't know if this is good practice or merely common practice.

I mean its certainly the case on something like a Linn, Thorens or Michell, but there you are talking about a serious degree of bounce, rather than the little bit of give we are going to see here. If I think of a deck that has a bit of give in the plinth (rather than full blooded suspension), the Roksan Radius 5 comes to mind. The compliant layer is below the piece of plinth where the bearing and the arm are mounted.

I must admit I don't know.

Don't see why not so long as it doesn't come too close to the cartridge.

Er. refresh my memory ... what point about the feet

 

You need to decide what sort of feet you are going to place under the deck. This needs to be decided as any change in their thickness will change the position of the platter relative to the pully. You would then have to raise / lower the motor pod to re align (have i spelt that right ) them.

How far is too far

I don't see an issue with the design, re armboard on top part of plinth. IMO the high mass of this part along with compliant layer should make it act like a seperate plinth. Decks seem to fall into two main camps, 1) arm board fixed to same piece, decks with or without suspension. 2) arm is fixed to seperate massive high mass pod, decks costing 10 K. Perhaps it's only been done this way because everybody does it this way !

We may have reached new heights in deck design


However I will yield to your greater knowledge

 

Okay. I'll dig in the spare parts bin and see what I can find. There are some quite nice pieces on the Xperience - large aluminium cup that screws onto the bottom of the plinth, a sorbothane insert and aluminium cones underneath. Height adjustable. Might do the trick. Might need sinking into the platter some or it could all ride a bit tall.

I was going to send you the parts I have over the next few days, but it might be 4 weeks before I can get hold of some nice feet. I'll check.

You've got me I dunno, but 3 or 4 cms probably - I say that because the latest Pro-Ject uses a similar platter but with opposing magnets underneath the platter and on the plinth (means the platter still has the same mass and momentum but much less "weight"). They are reporting no problems re MC carts and that designs puts fairly strong magnets within about 4 cms of the cart.

Looking at the plots - if the steel sheet is underneath the platter, I don't see it being a problem.

Unfortunately I don't have greater knowledge I suppose with a bit of smarts we could do it so both could be tried, do you think?

 

Sounds fine

I am going on holiday for a week on Saturday, so I'll wait to hear.

Let me know if you are happy with overall concept, and I will have a look for suitable plywood upon my return.

I would like to get hold of the arms you are wanting to use, so I can draw them up, and sort out clearance holes etc. I'll do some more plots, then if you are happy, I will cut a plywood sample for you to check alignment and geometry etc.

regards

 

Back from the snow

Hi Tony

Back now and back to the grind of normal life !

any further thoughts on the deck, next step ?

regards

 

Hi Granville,

Hope you enjoyed the break. Next step is for me to send you the parts, so that you have something real to mess with.

Only other thoughts after ahving a long chat with Zanash on the sunject regards those mild steel plates. Still some concern that they might set up some spurious magnetic fields that could affect the cartridge - are there any alternatives?

 

Thanks Tony, had a fantastic time, you realise what a crap hole the UK is when you visit Austria. The people a so very nice, the country is clean and tidy and they eat quality food. I wish I was back there now.

I suppose we could use Aluminium plate, but to get the mass it would need to be very thick. Brass would be a good choice, easy to work with and if I can find a high Pb content alloy, then all the better.
I guess that stainless would be a good bet, very expensive though and hard to work with.

I'll look into costs and availability.

Possible to use mild steel on the bottom and stainless at the top ?
The top sheet would act as a shield, if the bottom plate developed a magnetic flux, unlikley though I'd have thought.

If you are going to send anything, have I given you an address

 

Granville,

Hi, sorry for not getting back immediately. PM your address over and I'll organise some stuff to go your way. I suppose the thing to do is work out roughly how much mass would be sacrificed. I mwan yes a 10mm ali plate is going to be less massy rthan mild steel ... but its not exactly going to be a featherweight either I suppose.

Tony

 

Hi Tony

Have got some costs on metal for the deck, the price of Brass / Copper is totally mad at the moment. 2M x 1M x 9mm £910.00 + vat

Therefore to keep the price sensible how about laminating 3 sheets of 3mm stainless. If we use a suitable adheisive the resulting laminate would be very very heavy but also acoustically dead. exactley the result we are after

imo this would be an affordable but acceptable option.

It may be that 2 pieces will prove ok for the top section, I'll wait and see when I get all the bits.

regards Ian

 

:mana: Good lord. That's just silly ridiculous money.

At that price one might as wel go and buy a bloody record deck

Laminated stainless ... okay, for the amount we need I take it its not quite so silly.

I'll get it all in the post to you tomorrow. been a bit snowed under.

 

This metal is just to add mass ?

I'd really think twice about any Iron compound......

what about aluminium....or even perspex

there would be no issues with parasitc currents or stray magnetic feilds ...if it's just mass / damping you can get a load of those fake lead wieghts that fishermen use...the tiny little balls. You could fill a cavity in the bass of the plinth with them.....if you allow some movement this will aid damping. I don't mean so they can slop arround but if they are allowed to find there own best position ..like atoms in a crystal.

Anyway thats my two pence worth !

 

Granville, what do you think? the fake lead balls idea sounds sensible and cheap.