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rookster 5th August 2003 06:16 AM

DIY Turntable plinth
 
I don't want to re-invent the wheel, but I have a couple of ideas for a plinth for my DIY turntable, but I need some advice from others.

My thoughts are;

Solid Jarrah chopping board drilled to take the spindle and tonearm. Nice looking but expensive.

Laminated MDF plinth, painted a pretty colour. Cheap and heavy.

Laminated MDF plinth with pockets for sand or lead-shot. More labour intensive, but well damped. Sand is cheaper, but lighter. What is best?

I also have access to a nice round Jarrah chopping board that could be used as a platter. It looks like it was turned. It too is expensive, but would look great. I was thinking of adding periferal brass weights to increase inertia and reduce any likelihood of imbalance due to variations in wood density.

What do you think?

Brett 5th August 2003 07:48 AM

Re: DIY Turntable plinth
 
Quote:

Originally posted by rookster
Laminated MDF plinth with pockets for sand or lead-shot. More labour intensive, but well damped. Sand is cheaper, but lighter. What is best?
IME, this one. Mass, mass, mass.
Lead shot is reasonably expensive, about $A30/10kg in the guns shops in Fortitude Valley. Legal to buy too, but don't laugh maniacally or talk to an invisible friend when you're in the store.

My DD TT's and my suspensionless Gyro have very heavy plinths that are full of a leadshot, fine sand and mineral oil mix. When you've finished routering out the holes in the plinth, coat it inside and out wirh epoxy resin. Inside it will make it watertight for the oil, and outside, once sanded gives a great smooth finish that won't look like laminated MDF when it's done.
Forgot to mention to laminate with epoxy too.

A pic is worth a thousand words right?
http://www.teresaudio.com/haven/
Go to Teres TT, and look at the construction pix. Mine is similar, but I have a big motor assembly in the middle.

Quote:

I also have access to a nice round Jarrah chopping board that could be used as a platter. It looks like it was turned. It too is expensive, but would look great. I was thinking of adding periferal brass weights to increase inertia and reduce any likelihood of imbalance due to variations in wood density.
Here are some ideas
http://www.teresaudio.com/t-265.html
(check out the rest of the site too) as well as
http://www.redpoint-audio-design.com/

I don't know what you're using as a bearing, but it'd want to be good to bother with all the effort.

Do you have access to a lathe?

BobM 5th August 2003 06:08 PM

How about Corian
 
Find a kitchen contractor that installs Corian countertops. He's probably got a stack of sink cutouts in a wide variety of colors. Find one you like. Have him cut it to your dimensions and bond 2 1/2" pieces together, making a 1" plinth. Let him do the work - Corian can be dirty to cut and sand, and he's got the tools and the glue and the experience.

Enjoy,
Bob

rookster 5th August 2003 09:59 PM

BobM,

I do have a friend who builds kitchens. I will ask him. I was thinking of a plinth about 50mm (2") thick at least.

Brett,

I assume you are from around Brisbane also. I think I know which gun shop you mean. I had thought of ringing them up for a quote on lead shot. I take your point about sealing and using epoxy resin.

I have purchased a Teres bearing which will fit into something about 50mm thick.

I do have access to a lathe. What did you use as a platter? I am thinking acrylic, PVC or the wooden one I mentioned. I can machine the platter here at work during lunch time.

wrankin 7th August 2003 06:03 PM

More on Corrian
 
What are the thoughts about corrian instead of acrylic as a platter material? Is it easier to machine? Has anyone played with this?

Thanks,

-b

fdegrove 7th August 2003 08:59 PM

Hi,

Quote:

What are the thoughts about corrian instead of acrylic as a platter material? Is it easier to machine? Has anyone played with this?
Acrylic, AKA metacrylate as the advantage of having an impedance characteristic that's very close to vinyl.
In fact it's only slightly higher making for a good path to drain away energy from the record into the platter with little chance for back reflections.

It's not easy to work with, has to be treated with linseed oil craie to make it anti-static but has the advantage of being a monolithic polymer where as corian is much more difuse in structure and behaviour.

It would probably be O.K. as a plinth material but would be way down on my list as a platter material.

Just my 2 cents,;)

Brett 7th August 2003 11:16 PM

Quote:

Originally posted by fdegrove
Acrylic, AKA metacrylate as the advantage of having an impedance characteristic that's very close to vinyl.
In fact it's only slightly higher making for a good path to drain away energy from the record into the platter with little chance for back reflections.

PVC is available here at similar cost to acrylic, and I think that would give an even better impedance match. I use it as platter mats on two of my TT's.

Redpoint is the only manufacturer I know that uses it as a platter material.

My opinion is that acrylic looks better and that's why it's used more.

fdegrove 7th August 2003 11:27 PM

Hi,

Quote:

My opinion is that acrylic looks better and that's why it's used more.
Nope.

Better do the homework on this, Brett..

Quote:

and I think that would give an even better impedance match.
While you may want to augment perceived record mass on the top layer of the platter, this is not a material you'd want to use throughout...

We want to sink energy, not reflect it back to the stylus.

Cheers,;)

analog_sa 8th August 2003 08:55 AM

Quote:

We want to sink energy, not reflect it back to the stylus.
Surely a better impedance match, such as offered by PVC will reduce reflections.
On a different note i've used the same thickness of PVC and Perspex as equipment shelves and greatly prefer the intrinsic sound of Perspex.

cheers
peter

Nat Eddy 8th August 2003 01:54 PM

Could we have a little more explication of what you all mean by 'better' impedence match? I assume that better impedence match ought to mean the impedences are similar, so that (theoretically) there isn't much of a boundary. But of course there is, in fact, a layer of air between the record and the platter, even if it is only in the grooves (this assumes a perfectly flat record and a similar platter -- we should be so lucky). What, if any, effect does this have? And why is fdgroove so dismissive of impedence matching? Am I missing something?


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