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View Full Version : Granite plinth or birchply + SUT or how to save some money.



Wakefield Turntables
25-12-2013, 21:37
OK, you own a garrard 301. Some would say that the ultimate plinth is Granite. Personally I found this option costly and sonically no better than ply. I found that birchwood ply + a SUT was a far superior and cheaper solution to provide superior sonics than a granite plinth. Personally I think granite plinths are a fad and no better than ply. Controversial? Lets have your comments...... :mad:

walpurgis
25-12-2013, 21:45
Granted some TT motor units are heavy, but there's a limit to how much mass a plinth would need. Rigidity and a lack of resonance (within and around the audio bandwidth) should be the main considerations I'd have thought.

Wakefield Turntables
25-12-2013, 21:48
Well granite to my ears really dampens the 301 too much.

Clive
26-12-2013, 00:17
Granite is not an ideal plinth material IME. I'm not surprised birch ply was better. At least your experience bears our what I've heard.

PaulStewart
26-12-2013, 01:34
When I was working with Loricraft/Garrard we had a look at stone plinths including marble, slate and granite. We found that sporious energy was trapped in the stone plinths and reflected back into the deck. The Loricraft plinth uses Harold Leak's trick of using squash balls to isolate and disperse this spurious energy. The vestigal version of this plinth uses birch ply and does a good job.

Wakefield Turntables
26-12-2013, 11:17
Somewhere on the net exists an article about how various plinth materials resonate and how they spread and remove the various spurious nasties that can get back into the deck. I choose plywood for this reason and because it was so much cheaper than slate. The squash balls are something I'm going to have to try.

JazzBones
26-12-2013, 11:51
Somewhere on the net exists an article about how various plinth materials resonate and how they spread and remove the various spurious nasties that can get back into the deck. I choose plywood for this reason and because it was so much cheaper than slate. The squash balls are something I'm going to have to try.

Andy, sometime ago I was talking to Terry O'Sullivan of Loricraft at a show and he showed me his usuage of squash ball isolation on his modified 301, 401 TT and he does in fact use squash balls but not the ball as a whole. They are cut in half so that might be worth keeping in mind if you experiment? T O'S told me that he had also experimented with sorbothane but his preference was for halved squash balls.... don't ask what velocity dot grading :confused:

I've heard Garrards in the past and liked them especially T O'S top dog, the 501 which he has manufactured from scratch I believe. Will be interesting to follow your mod progression on your 301 especially as you also use a high mod/spec Techie. The latter I use as No1 in my system but sometimes and on some records I would like it to sound just a little bit different. Maybe the odd touch of romance now and again? I guess thats what makes me go back to my modded LP12 every now and again.

Hope 2014 is going to be a good'un fo all of us :)

MCRU
26-12-2013, 12:11
Its' not just about the plinth, what is the entire TT sat on? how is it coupled to the floor?

a granite plinth sat on a glass rack on a concrete floor will sound totally different to the same plinth on a wooden rack on a carpeted wooden floor

and so on and so forth so to dismiss granite or slate or corian etc is a bit silly IMO

PaulStewart
26-12-2013, 12:17
Hi Ron, When I worked for the company, doing the very tests you mention talking to Terry about, the squash balls were not halved, they were in a tight recess so only half showed. I think my brother still has the prototype sorbothane block plinth.

We found speed rating did not effect sound, but one trick that did work, but only slightly was to punch a hole in the rear left (motor corner) ball and fill it with silicone rubber as that was the corner that needed the greater support. Almost no difference in sound however.

Cheers

Ali Tait
26-12-2013, 12:50
Slate is the best I've heard to date. From what I've read, granite is a no no due to it's crystalline nature. Slate is a natural CLD material. My 401 sounds great in it's double layer slate plinth.

brian2957
26-12-2013, 13:00
Sounds ,and looks , fantastic too .

Mr Kipling
26-12-2013, 13:11
Last night when I saw this thread I was going to suggest that energy might be getting reflected back with granite, but I went to bed. It used to said the reason the Ittok worked well on the LP12 was due to the fibrus armboard absorbing the energy from the arm. When mated to solid metal armboard decks it was said to perform less well as the energy from the arm was being reflected back into it.

One thing I have never seen with any 301/401 plinth (or the vast magority of decks, for that matter) is having the arm on it's own chassis, which surely must isolate it from noise. It's what I would do.

Mr Kipling
26-12-2013, 13:19
Slate is the best I've heard to date. From what I've read, granite is a no no due to it's crystalline nature. Slate is a natural CLD material. My 401 sounds great in it's double layer slate plinth.

JBL seemed to think slate was ok.

The Grand Wazoo
26-12-2013, 13:45
The idea that slate is made of layers is wrong - it's made from individual grains continually laid down over a long period of time.

Ali Tait
26-12-2013, 14:10
Didn't say it was, just said it acts LIKE a CLD material. However, my other half, who has a Masters in geology, tells me it does form in layers.

Ali Tait
26-12-2013, 14:17
Informative article here-

http://www.bbc.co.uk/bitesize/ks3/science/environment_earth_universe/rock_cycle/revision/5/

Seems it does indeed form in layers during the high pressure part of the formation process.

Clive
26-12-2013, 14:43
One thing I have never seen with any 301/401 plinth (or the vast magority of decks, for that matter) is having the arm on it's own chassis, which surely must isolate it from noise. It's what I would do.
The twin tier plinth ftom the now defunct Slatedeck had the armboard sitting on the lower tier.

Ali Tait
26-12-2013, 14:44
As does mine.

The Grand Wazoo
26-12-2013, 14:45
Well, I think it is a question of degree Ali. You will find a layer of slate, among other strata, but the entire slate layer is formed from the compression of shale is it not? Since shale is a sedimentary rock, it's made from material laid down from a suspension in water.

Ali Tait
26-12-2013, 15:01
Which will form in layers surely? :D

Clive
26-12-2013, 15:02
I've not seen how roofing slates are cleaved from larger pieces of slate, does this process rely on some form of layering?

The Grand Wazoo
26-12-2013, 15:03
.....just said it acts LIKE a CLD material.

I'm afraid this is another misnomer as well.
I think that CLD's are sandwiches of stiff and squishy materials.

The Grand Wazoo
26-12-2013, 15:05
Which will form in layers surely? :D

No, when a river silts up, it does it gradually: grain by grain, not by dumping everything down in one go, then again later in another layer.

The Grand Wazoo
26-12-2013, 15:06
I've not seen how roofing slates are cleaved from larger pieces of slate, does this process rely on some form of layering?

No, the cleaving happens because the particles separate along the line in which the force is applied. I think you'll find that there is a 'grain' to slate, which means it won't cleave in the direction in which the metamorphic pressure that Ali's link refers to lies, but this is not the same as a layering effect.

Clive
26-12-2013, 15:09
I'm afraid this is another misnomer as well.
I think that CLD's are sandwiches of stiff and squishy materials.
That though too is a matter of degree. I've seen ply and lead layers but also simply different types of ply or even the same ply with the grain in varied orientations.

Ali Tait
26-12-2013, 15:10
Well according to the link, it says the crystals form in layers, which I guess is why it can be split into thin sheets.

Ali Tait
26-12-2013, 15:14
No, when a river silts up, it does it gradually: grain by grain, not by dumping everything down in one go, then again later in another layer.

Yes, but what is laid down is going to differ over time, resulting in different compositions being laid down in layers.

The Grand Wazoo
26-12-2013, 15:18
Well, I regard a layer as something which has a definite boundary at it's top and at it's bottom. If you define it as a strata of different material with an indefinable boundary, then, yes, you will have a layer!

Ali Tait
26-12-2013, 15:25
Looks like layers to me -

http://img23.imageshack.us/img23/9066/7zn4.jpg (http://imageshack.us/photo/my-images/23/7zn4.jpg/)

Clive
26-12-2013, 15:26
Well, I regard a layer as something which has a definite boundary at it's top and at it's bottom. If you define it as a strata of different material with an indefinable boundary, then, yes, you will have a layer!
You could layer slices of meat together, are these boundaries sufficient for your definition? This is getting down to semantics.

Ali Tait
26-12-2013, 15:31
Reading further, Wiki states that slate is a foliated rock -

http://en.wikipedia.org/wiki/Foliation_(geology)

Ali Tait
26-12-2013, 15:32
...which to me, suggests that it will indeed act like CLD, and that's what my ears tell me it does when I listen to it.

PaulStewart
26-12-2013, 15:34
We had a three bird roast the other day, that's got layers and dissimilar materials, wonder what that would sound like as a plinth material :laugh:

The Grand Wazoo
26-12-2013, 15:37
Halal and kosher plinths?!

PaulStewart
26-12-2013, 15:41
Halal and kosher plinths?!

You could start with a full plinth and eat your way to an SE version to hear the difference :lol:

The Grand Wazoo
26-12-2013, 15:46
Reading further, Wiki states that slate is a foliated rock -

http://en.wikipedia.org/wiki/Foliation_(geology)

....and it mentions 'the extremely fine grained preferred orientation of clay flakes in slate'.

Which is the grain I referred to - not what I call a layer.
The actual material has already been laid down before the foliation begins.
Anyway, enough - I'm off to do some experiments with doner kebab meat.

Ali Tait
26-12-2013, 15:47
Pizza?

The Grand Wazoo
26-12-2013, 15:49
Yeah! - deep fried.

Ali Tait
26-12-2013, 16:07
Yum yum.

Mr Kipling
26-12-2013, 16:21
What about sand filling?

PaulStewart
26-12-2013, 17:01
What about sand filling?

Don't fancy it it a meat plinth :lol: Just had a thought, is doner digital shish?

On a serious note mass loading with sand and other such materials can work wonders, many years ago I got from my dad an SME plinth which had contained his TD124. I put a Garrard 301 in it and it sounded crap as had the Thorens. I replaced the base with ply which helped a lot then mass loaded it with sand and things really started to cook. The final version saw the addition of bitumen panels fitted to all internal surfaces and 25% lead shot added to the sand. By this time the arm was an Acos Lustre and the cart was an M75 and it sounded awesome :)

Ali Tait
26-12-2013, 17:01
Thought about making a sand filled box for the plinth to sit on.

MCRU
26-12-2013, 17:01
sand filled kebab, no thanks :lol:

Mr Kipling
26-12-2013, 17:57
Thought about making a sand filled box for the plinth to sit on.

Fancy having a go myself.

walpurgis
26-12-2013, 18:52
That's a thought I've had in mind for my next TT project. A sand filled plinth!

Not hard to do, just two sheets of MDF or other suitable material separated with spaced out MDF blocks and any edge or opening gaps sealed with MDF batons. Leave a hole in the back to pour the sand in of course. Fill with 'kiln dried sand', last thing you want is damp sand. Then shake and tap and keep topping up until there's no more settlement and plug the filling hole. Bob's your uncle!

Kiln dried sand is used by local councils to fill gaps in block paving and it can be obtained easily.

awkwardbydesign
26-12-2013, 20:17
Somewhere on the net exists an article about how various plinth materials resonate and how they spread and remove the various spurious nasties that can get back into the deck. I choose plywood for this reason and because it was so much cheaper than slate. The squash balls are something I'm going to have to try.
Here? http://qualia.webs.com/plinthbuilding.htm

Wakefield Turntables
26-12-2013, 20:22
Yep thats the one.

Ali Tait
26-12-2013, 20:44
Here's a good article on a sand filled base-

http://www.tnt-audio.com/clinica/sandblaster_e.html

Mr Kipling
26-12-2013, 20:51
Thanks Geoff. I was wondering how to deal with the curved cutout area for a 401 with regards sealing it.

awkwardbydesign
26-12-2013, 20:56
When Cat's squirrel talks about constrained layer damping using a shearing mechanism to dissipate energy, it reminded me of the last speaker cabinets I made. The design was a failure, but the cabinet damping was not. 18mm birch ply with bitumen damping inside (I make my own from heavy roofing felt with slate chippings, 2 or more layers, all glued with water based bitumen paint) and 15mm limestone panels stuck to the outside with Rewmar flexible polymer adhesive (designed to allow sideways movement of solid wood floors). In 40 years these are the deadest cabinets I have ever made. I hate the sound of cabinets, and these were dead, dead, DEAD! Pity I used the wrong drivers! With the new speakers I have followed the designer's instructions, but I can hear the cabinets. The design is a success, but the damping could have been so much better.
The flexible adhesive was the key, I believe.

Mr Kipling
26-12-2013, 21:12
Thanks Ali. Feel galvanised into some action to get a 401 into a proper plinth.

John
26-12-2013, 21:18
Slate works really well with Idler drives

walpurgis
26-12-2013, 21:19
Thanks Geoff. I was wondering how to deal with the curved cutout area for a 401 with regards sealing it.

Make a curved cutout spacer the same thickness as any spacers that will be used just to separate the top and bottom boards of the plinth. The cutout spacer should match the main cutout aperture on the inside of where the TT will go and just make it maybe 20mm wider all round outside and glue this in place at the same time as all other spacers and batons.

Remember that any areas where mounting bolts or screws go through will need to be solid, so glue bigger spacer pieces here. Best to cut all spacers, batons and cutout spacer from the same sheet of material. That way they should be all matching thicknesses.

I'd do all the gluing of pieces on the bottom first, allow glue to partly dry (maybe 20 mins) and turn over and lay on a very flat surface with a thick board and some weight on it. Gluing the top on 24hrs later. Me, I'd leave the filler plug removable, just for occasional topping up maybe, or experimentation with alternative filling materials (polythene granules spring to mind, they work, I've used them in speaker stands. They damp well but are light).

Mr Kipling
26-12-2013, 21:26
When Cat's squirrel talks about constrained layer damping using a shearing mechanism to dissipate energy, it reminded me of the last speaker cabinets I made. The design was a failure, but the cabinet damping was not. 18mm birch ply with bitumen damping inside (I make my own from heavy roofing felt with slate chippings, 2 or more layers, all glued with water based bitumen paint) and 15mm limestone panels stuck to the outside with Rewmar flexible polymer adhesive (designed to allow sideways movement of solid wood floors). In 40 years these are the deadest cabinets I have ever made. I hate the sound of cabinets, and these were dead, dead, DEAD! Pity I used the wrong drivers! With the new speakers I have followed the designer's instructions, but I can hear the cabinets. The design is a success, but the damping could have been so much better.
The flexible adhesive was the key, I believe.

That reminds me of the Townsend Glastonbury speakers. These were lined with a type of plaster of Paris which was slowly kiln-dried and was semi-solid when dried. It was then treated to a covering of some carpet material.

Mr Kipling
26-12-2013, 21:38
Make a curved cutout spacer the same thickness as any spacers that will be used just to separate the top and bottom boards of the plinth. The cutout spacer should match the main cutout aperture on the inside of where the TT will go and just make it maybe 20mm wider all round outside and glue this in place at the same time as all other spacers and batons.

Remember that any areas where mounting bolts or screws go through will need to be solid, so glue bigger spacer pieces here. Best to cut all spacers, batons and cutout spacer from the same sheet of material. That way they should be all matching thicknesses.

I'd do all the gluing of pieces on the bottom first, allow glue to partly dry (maybe 20 mins) and turn over and lay on a very flat surface with a thick board and some weight on it. Gluing the top on 24hrs later. Me, I'd leave the filler plug removable, just for occasional topping up maybe, or experimentation with alternative filling materials (polythene granules spring to mind, they work, I've used them in speaker stands. They damp well but are light).

Thanks Geoff. I'm chomping at the bit. Hope the enthusiasm lasts.

At the back of my mind I've also had the idea for a self-centering turntable support. I don't know if it would really work with the mass involved.

walpurgis
26-12-2013, 22:06
Thanks Geoff. I'm chomping at the bit. Hope the enthusiasm lasts.

At the back of my mind I've also had the idea for a self-centering turntable support. I don't know if it would really work with the mass involved.

Do you mean self levelling? A large rectangular 'bean bag' might achieve that and add a bit more isolation into the bargain.

Mr Kipling
26-12-2013, 22:18
Do you mean self levelling? A large rectangular 'bean bag' might achieve that and add a bit more isolation into the bargain.

Never thought of that.

Yes I was meaning self-levelling. A single-point gimbal bearing is what I have in my mind.

walpurgis
26-12-2013, 22:33
Never thought of that.

Yes I was meaning self-levelling. A single-point gimbal bearing is what I have in my mind.

For that to work you'd almost certainly need to use some form of hydraulic damping and maybe weak positioning springs to produce travel limits and have a quicker restore action than gravity/mass alone would provide.

DiveDeepDog
26-12-2013, 22:34
Having both ply and slate, I also prefer ply. I like the enthusiasm, but feel some of the ideas will lead to too much dampening.

I've experimented with sorbothane and squash balls and find they suck the life out of the tunes, Mission 775SM is a perfect example (to me) of over damped materials, sorbothane and MDF but the best platter and bearing engineering can't lift it above an average deck.

I'd be interested in hearing one of the resin deck around, but some of the feedback leads towards losing the Garrard-ness in favour of accuracy (something I've heard about the Classic 301), its all about getting a balance within the system, and taking it as a whole, not in isolation.

I went to great effort to isolate the arms on this plinth, they're only joined at the bottom layer;
http://farm6.staticflickr.com/5446/8759810068_1a5f9c6fef_o.jpg (http://www.flickr.com/photos/49381909@N08/8759810068/)
Garrard 401, twisted Dovetail (http://www.flickr.com/photos/49381909@N08/8759810068/) by levs the diver (http://www.flickr.com/people/49381909@N08/), on Flickr

but isolating an arm boards is just as affective

* My current favourite is ply plinth with either slate, or Corrian arm boards

walpurgis
26-12-2013, 22:38
That brings back memories. I had a 401 with 774 arm. The 401 is long gone, but the 774 is still in use. It's on my Toshiba SR-370, which sounds better (to me) than the 401 ever did.

anubisgrau
27-12-2013, 11:11
i think we're talking apples and oranges here. you can't talk plywood vs slate per se, it's about implementation and what sound you're after, do you want it cleaner or warmer. you can easily overdamp with thick, big mass ply plinths and make garrard sounding thick and congested. i believe actually it's easier to make it sounding clean and fast with slate, as long as you don't make a 50kg plinth - a good thing about slate is you can actually get away much cheaper than you can think of - 2cm top board is just enough regardless of if you go skeletal or closed box. you can actually do great results with old (and crap) SME plinth if you replace top board with 2cm slate do some plinth damping and add mass. and you still have the look of era where 401 was produced.

awkwardbydesign
27-12-2013, 15:30
That reminds me of the Townsend Glastonbury speakers. These were lined with a type of plaster of Paris which was slowly kiln-dried and was semi-solid when dried. It was then treated to a covering of some carpet material.
I think you'll find the kiln was Malta! I went to his "factory" when I was on holiday there, trying to get a pair of the tweeters he used. I already had the Jordan JX150s. No luck, but I talked to his workforce. One Maltese guy in a big empty warehouse! As I recall, he used 2 densities of plaster stuck to the pile of Wilton carpet, stuck to the metal outer skin. Lovely, but laborious, idea. I would still like to try a pair. I have found Max very easy to talk to, and ready to take on new suggestions. Or maybe he just humoured me!

awkwardbydesign
27-12-2013, 15:36
That brings back memories. I had a 401 with 774 arm. The 401 is long gone, but the 774 is still in use. It's on my Toshiba SR-370, which sounds better (to me) than the 401 ever did.
Still got my 774 too. Them little red plugs and sockets are a bugger to source. I found them years ago, but can't remember where now! :scratch:

Clive
27-12-2013, 17:13
i think we're talking apples and oranges here. you can't talk plywood vs slate per se, it's about implementation and what sound you're after, do you want it cleaner or warmer. you can easily overdamp with thick, big mass ply plinths and make garrard sounding thick and congested. i believe actually it's easier to make it sounding clean and fast with slate, as long as you don't make a 50kg plinth - a good thing about slate is you can actually get away much cheaper than you can think of - 2cm top board is just enough regardless of if you go skeletal or closed box.
This totally echoes my experience. I also tried squash balls and roller blocks, all have their own signature with slate being the cleanest and most transparent, it gets warmer as you go thicker. I use 30mm with my 301, twin tiers.

Ali Tait
27-12-2013, 17:19
Yep, agreed. My plinth is two tiers of 30mm, arm board decoupled and sitting on the bottom tier. Allows the best of the 401 to come through IMHO.

Mr Kipling
28-12-2013, 20:46
That brings back memories. I had a 401 with 774 arm. The 401 is long gone, but the 774 is still in use. It's on my Toshiba SR-370, which sounds better (to me) than the 401 ever did.

Geoff. . . Just when I was getting enthusiastic. Nevermind, I'm still going to try it. At one time I was thinking of using a single layer of slate about an inch think, but I'm not a huge fan of the looks of slate.

As for the support, some means of limiting travel would be needed. Never thought of springs. What I was thinking of was a heavy underslung weight to lower the centre of gravity and silicone damping on 3 outtiggers. The idea was just to issolate the deck as much as possible.

Richard, I'm pretty sure it was Jon Bamford who reviewed the Glastonburys in Hi-Fi Answers. Don't remember Madrid getting a mention, but I could be wrong. I remember it saying the plaster surface was flexable and not hard. Wasn't sure if the carpet was Axminster or not. Top quality all the same. Non of your cheap foambacked rubbish. I believe they were rather heavy.

I'm wanting a red plug and socket myself.

awkwardbydesign
29-12-2013, 15:58
Richard, I'm pretty sure it was Jon Bamford who reviewed the Glastonburys in Hi-Fi Answers. Don't remember Madrid getting a mention, but I could be wrong. I remember it saying the plaster surface was flexable and not hard. Wasn't sure if the carpet was Axminster or not. Top quality all the same. Non of your cheap foambacked rubbish. I believe they were rather heavy.

I'm wanting a red plug and socket myself.
Malta, not Madrid! The review I read mentioned plaster of paris, and I think Herculite. The drivers were mounted to the plaster and decoupled from the steel (?) casing. Definitely stuck to the pile of the carpet which had been stuck to the metal. It took six (or is that 12?) pourings as each pour had to set before turning for the next one. Of course this was what I read, but definitely saw the factory on Malta. I don't know how the reviewer got at the plaster to feel it. And yes, they are heavy! I have considered the carpet + plaster method myself, but it's a bit messy to do at home.

Mr Kipling
29-12-2013, 16:43
Sorry Richard. Short-term memory isn't what it used to be.

I think Jon Bamford just gave a general description of their manufacture. I'll have to dig it out. He did like them.

Have you ever made any round cabinets like JR 149s? Often wondered if it could be done using a inner and outer skin of glass fibre/kevlar and filling the gap with sand or expanding foam and using the drivers and crossovers from a commercial design, just to see if the sound would be any different from that using a typical square box.

awkwardbydesign
29-12-2013, 19:47
I've made several tubular cabinets using heavy cardboard tubes, 6"-8" diameter, ply or MDF ends with similar fronts and dividers. Transmission lines with small Audax drivers, I was planning to market them but never did. And yes, I think they sound better than boxes. Also with curved earthenware water pipes, but they rang a bit. If you can pick up (pinch!) some of those yellow plastic pipes from gas or water roadworks, they work well too. Many different sizes, too. Just fit the flat fronts before you slice the pipes, as they are under tension!
And thinking about the Glastonburys, if the inner plaster was browning, that would feel soft.