GARRARD 401 MAHOGANY PLINTH

[mouse]

Hi peeps

i have to decide on a material for a plinth for my 401. I have access to a lovely piece of mahogany 40mm thick however it is only 14" deep so it will mean sticking two pieces together - my joiner ensures me he uses resin rather than a standard wood glue so to all intents and purposes would be as solid as a 1 piece block. any thoughts out there? Also is mahogany a good option (sapele - i think is the spelling)?

[Bigears]

Sapele is a popular wood, favoured particularly in the 1970's for furniture due to the stripy grain pattern. Personally, I would use it for the edges and use birch ply for the motorboard.

[cats squirrel]

Hi peeps

i have to decide on a material for a plinth for my 401. I have access to a lovely piece of mahogany 40mm thick however it is only 14" deep so it will mean sticking two pieces together - my joiner ensures me he uses resin rather than a standard wood glue so to all intents and purposes would be as solid as a 1 piece block. any thoughts out there? Also is mahogany a good option (sapele - i think is the spelling)?

have a look here, hopefully you will be able to sort the facts from the beliefs.


http://www.vinylengine.com/phpBB2/viewt ... sc&start=0

[Chris H]

Birch ply, the void free metric stuff. Try a Sapele armboard, or well aged Ebony. Try a layer of mdf in there somewhere, or Basswood. Maybe a layer or pocket of something dense.

Simple stack of Baltic Birch ply, with an armboard of some different material is a sure winner. Bronze for the armboard is also a possibility for an armboard layer or armboard.

[J.D.]

have a look here, hopefully you will be able to sort the facts from the beliefs.

Could you offer an insider's-guide to the facts vs the beliefs ?
That would be very interesting. And maybe a roadmap to correct plinthing strategies.

[mouse]

Hi Cats Squirrel some of this is above my head. My dilemna is i have the opportunity to use this mahogany (quite cheap source - budget is forever a massive factor in my case) . There is enough to double or even treble the thickness (40-120mm) of the plinth. Supposing i am using this material, in your opinion ar there any other building techniques (i'm thinking sandwiching with something else perhaps) that you can advise on.

Hi peeps

i have to decide on a material for a plinth for my 401. I have access to a lovely piece of mahogany 40mm thick however it is only 14" deep so it will mean sticking two pieces together - my joiner ensures me he uses resin rather than a standard wood glue so to all intents and purposes would be as solid as a 1 piece block. any thoughts out there? Also is mahogany a good option (sapele - i think is the spelling)?

have a look here, hopefully you will be able to sort the facts from the beliefs.


http://www.vinylengine.com/phpBB2/viewt ... sc&start=0

[Chris H]

Labor is likely to be a significant expense in this venture, even if it is measured purely in time.

Baltic Birch is your best bet.. but, If you must use solid wood, Mahogany is probably a better choice than many woods. Its resonant qualities are not too lively, but not dead, not that far from Cherry, which Shindo uses for his plinths. ( The use of thin slices is a whole different story though.) It is relatively stable, and does not ring as much as some wood. Actually , the Mahogany plinth is likely to sound better than some of the damped plinth schemes proposed in the other thread mentioned. Make sure it is completely dry, or it may warp or come apart. Slicing the Mahogany in thin layers, then laminating in alternating grain directions would yield a very stable block. You might consider using one layer, joined for width, with a very precise, stiff spline in each end grain end, to help keep the slab flat, pinned in the middle of the plank, not glued the entire length or it may cause the plank to split. This can also be an area for the artistic element to come into play. Then designing a plinth along the Loricraft lines. Finding cores or pieces of slate, bronze, brass, and precisely 'letting' them into the underside of the plinth might be an interesting idea to try. Maybe a decent sized chunk of bronze under the armboard side of the plinth.

Hard to say until you try...

If I had to choose a solid wood for building a plinth for a 401, Mahogany would be one of my top choices because of its tonal qualities, and it's stability.

As far as 'the best way to build a plinth' there are many ideas. Probably many strong opinions come from people who have very little, or no actual experience in designing, building PLINTHS, and listening to the results, people who have built maybe one or two, and therefore know the whole world of plinths and the relationship of all components in a turntable, or, maybe they own an SME, Clearaudio, or Acoustic Raven turntable, read the brochure about this or that factoid and some convincing words describing the plinth and why theirs is the best, and extrapolate a world view from this. As far as I know, there is no measuring equipment that you can set in front of your system, and read the results saying 'this sounds good', other than the human ear. True, that we can measure many things, but, in the real world, there are so many things that we cannot accurately explain. Theories yes... and many theories have at least some validity....

[mouse]

thanks Chris H perhaps you could also explain to me the comparable benefits between gluing say 2 layers together or using one layer sat on spikes on another massive layer but unjoined, and this bottom layer also on spikes (skeletal)? a pal of mine had a heavy mass plinth (plywood i think) but says he's got best results when just using the top layer on some cone feet??

Also (if using mahogany which is pretty much nailed on now) should the t/table baseplate sit directly onto the wood plinth or should i introduce some "damper" there, rubber grommets or some other material?

Probably will use an SME and a HADCOCK arm - what do you think of the latter as a partner.? (using MM or high output MC cartridges)

mouse

[J.D.]

My general take on the "stacked ply layer" vs the "skeletal" is that it has more to do with the intrinsic quietness of your deck's mechanics than anything else.

A highly-maintained, quiet & behaved 3/401 can do brilliantly well on a good skeletal design. An older, looser-tolerance, higher noise-floor version of 3/401 will probably have better luck with the rumble-attenuating stacked birchply standard model.

So while all will sound good on the stacked birchply, the super-quiet ones can get away with a skeletal.

(if you've got time you may find some of the info worthwhile at my site, http://home.earthlink.net/~transcrubbers/ )

Good luck.

[J.D.]

Chris, agree with much of what you've posted thus far.. I think there is a better answer, though, to the idea of building new experiments again and again... Especially if all you're after is a nice plinth that does what it's supposed to.

I think it's worth it to look at the majority of Garrard Plinths done post-1980 or so, and they are stacked birchply without too much exception. Yes, shindo, yes slate, sure, and the dozens of wacky experiments people have dreamed up, but -- for the one-&-done participant who doesn't want to be filling his house with sawdust & glue fumes for years before deciding, the modest stacked-birchply does the job for the garrard everyman.

There is absolutely nothing scientific about this, but, notably, it's proven itself around the world. Which is proof enough for many of us.

[Chris H]

I was suggesting two layers glued together as a means of increasing the mass of the plinth which will help act as a drain for vibration, and to give a likely increase in the stability of the finished 'plank'. If you do join two layers together, think about the type of glue you use. Titebond 3, or other wood glue will introduce water moisture into the wood, which will cause some movement of the wood. Since Mahogany is relatively stable, this effect is minimized depending on the grain pattern of the wood. If you have means to surface a thick, wide plank ( wide overhead sander) and have patience to wait three weeks after laminating the 'plank' then do so. Epoxy will probably exaggerate the ring in the wood, but will not introduce moisture problems. Epoxy may make a more visible line at the joint due to the slow set time, and very effective penetration of epoxy into wood. If you use epoxy, do your research, mix accurately, and remember to use an adhesive filler. A resin glue such as Unibond 800 is very good, as would be hot hide glue, if you are experienced with working with it. Wouldn't use polyurethane glues unless you are very careful in acheiving a very tight fit, and clamping well ( like in a vacuum press)

With a single layer of 40mm Mahogany, I would be concerned with warping and twisting over time. Perhaps if you used rigid columns between the layers, firmly fixed to top and bottom, you could minimize this. A little warpage in the wrong place could give you some problems in being able to achieve the correct azimuth in your cartridge setup. The plinth needs to stay flat. ( one of the disadvantages of solid wood)

With a massive Baltic Birch stacked plinth, mounting the motor plate directly to the plinth with no grommets will help to couple and drain vibration from the motor. With some plinths you may find the grommets to be helpful, like with a slate plinth.

As for tonearms for the Garrard, I like the newer SME arms better, 309, IV, V, 312, than the 3009 or 3012, though there is something to be said for the old school classic match-up. Arms with bias weights, damping plates, and other dangly extensions can amplify any vibrations making it to the tonearm, and noisy idler drives tend to vibrate. I do not know the Hadcock arms.

If you are going for a skelatal plinth with two layers of Mahogany, you might think about four very rigid columns separating the layers. Maybe some deep threaded inserts in the underside of the upper layer, through bolted from the underside of the bottom layer. Columns of 3" brass rod, or maybe 3" aluminum pipe, filled with lead shot, and maybe epoxy. The rigid mounted columns will help keep things flat.

J.D. I agree about the BB ply stack, it works very well.

[cats squirrel]

Hi Cats Squirrel some of this is above my head. My dilemna is i have the opportunity to use this mahogany (quite cheap source - budget is forever a massive factor in my case) . There is enough to double or even treble the thickness (40-120mm) of the plinth. Supposing i am using this material, in your opinion ar there any other building techniques (i'm thinking sandwiching with something else perhaps) that you can advise on.

Hi peeps

i have to decide on a material for a plinth for my 401. I have access to a lovely piece of mahogany 40mm thick however it is only 14" deep so it will mean sticking two pieces together - my joiner ensures me he uses resin rather than a standard wood glue so to all intents and purposes would be as solid as a 1 piece block. any thoughts out there? Also is mahogany a good option (sapele - i think is the spelling)?

have a look here, hopefully you will be able to sort the facts from the beliefs.


http://www.vinylengine.com/phpBB2/viewt ... sc&start=0

Hi mouse,
sorry for the tardy reply, but I'm on holiday, and can't always get to a computer. If you have decided on mahogany, then I can suggest how to make the best of it. And contrary to JD's beliefs, it is all about science, physics, material science and acoustics (yep, another science!).

As mentioned before, the plinth can be thought of as having three frequency regions, controlled by stiffness, mass and damping.

As you have chosen mahogany, lets have a look at it. It isn't stiff, but it may be stiff enough. The mass depends on its dimensions and density, so having decided on its breadth and width (as near in ratio to 1:1.61 for best results), its mass then depends on its thickness. It will vibrate most at certain frequencies (if excited) depending on the things I've mentioned before. These are the modal frequencies, or resonances. Now comes the down side.

Mahogany has a damping factor around 0.04, not a damping material, but about the same as plywood, and double that of mdf. As, at resonance, damping factor is 1/Q, the resonance peaks will have a Q of about 25, not a good thing. Only damping will bring these down. Then there is the critical frequency, which, once you have decided on the material, will depend solely on the material's thickness. I don't have data to hand for mahogany, but for plywood, it is 16kHz/mm, meaning a 100mm thick plinth will have a critical frequency of 160Hz. At this frequency, the plinth will be transparent to the sound, and above the critical frequency, it is controlled by damping, which it doesn't have! And they say glulam (glued laminate) plinths are good! If you make your plinth less thick, you lose mass. Bummer!

Having two or more spaced layers of solid mahogany will help, as long as they are of different thicknesses, to spread the resonance and critical frequencies. Of course, you could add damping! If not, your mahogany deck would sound, shall we say,'enhanced' say strong boomy bass, lively midrange and sparkling top end. If that floats your boat, you're onto a winner!

Good luck, <any questions, just ask>

ps connect the deck directly to the plinth, what you are trying to accomplish is to transfer the vibrations from the deck to the plinth, although, unless it has damping qualities, it isn't going to help much. Having a separate arm pod is a good thing, as mounting an arm directly onto a vibrating plinth isn't going to win any votes in the 'clarity and focus' department.

[J.D.]

Ever designed or built any actual plinths for phonographs, mr catsquirrel ?

If so, it doesn't quite seem to translate in your posts. Your post strikes me as something written about, say, croissants, from the point of view of a chemist. Nice theoretical analysis, not so clever re the actual resulting pastry.

Your remarks re 'separate armpod' run directly contrary to my own limited but not completely inconsequential experience, for example.

Ever designed & built any plinths out of solid hardwoods .. ? Or ply ? Done side-by-side comparisons on outboard vs onboard armpods ? It doesn't exactly invalidate your remarks if you haven't, but it would help to contextualize them.
Just like to know; that would help calibrate your commentary.

[cats squirrel]

Ever designed or built any actual plinths for phonographs, mr catsquirrel ?

If so, it doesn't quite seem to translate in your posts. Your post strikes me as something written about, say, croissants, from the point of view of a chemist. Nice theoretical analysis, not so clever re the actual resulting pastry.

Your remarks re 'separate armpod' run directly contrary to my own limited but not completely inconsequential experience, for example.

Ever designed & built any plinths out of solid hardwoods .. ? Or ply ? Done side-by-side comparisons on outboard vs onboard armpods ? It doesn't exactly invalidate your remarks if you haven't, but it would help to contextualize them.
Just like to know; that would help calibrate your commentary.

I see that you are taking the 'personal attack mode'. Because what I have to say (with the rest of science) is not what you have experienced, somehow it is my credentials that are called into question. Mmmm!

For the record (sorry) I have constructed plinths since the sixties, and continue to do so. I measure what I build, and listen to them. Measuring and listening show me the same thing (if they don't, I re-measure).

Let me tell you about my church. It relies on the components of a hifi system to reproduce what has been recorded without enhancement to give me the excitement. If it doesn't excite me, its because the original wasn't exciting. I don't want to add anything, I want to listen to the music, warts and all, and make my assessment.

I currently have four idler wheel drive decks, and one belt drive. I have owned (and built plinths) for a Thorens TD150, but it didn't give me what the idlers give. I still haven't played anything on my Michell belt drive tt, despite having bought it 4 years ago; the idlers are doing fine. I run a Goldring G99 with separate arm pod, and very advanced (technically) plinth, and I am getting the same kind of musical experience and enjoyment I get from my Leak troughline FM tuner, both of which being far far better than a mid priced cdp.

As I know a bit about science, including material science and acoustics, I don't need to make things out of inappropriate materials to test them. I assure you that SME's factory is not knee deep in failed prototypes, just in case inappropriate materials just might have been suitable as a tone arm material. That is why we have science.

I have had similar responses from people who swear by slate plinths. They are still chasing their tails, looking for something better; now, their sheds/garages are knee deep in prototypes!!