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Dead Wax Cafe

 

CONSTRUCTION DETAILS FOR THE SANDTABLE


A HEAVY DUTY TURNTABLE ISOLATION SYSTEM

By David Allcock

The Sand Table was designed to address a real need here in the UK, for a turntable support that would deal with a turntable which was wider than 19" and could be floor mounted bringing the turntable to a reasonable operating height. Any turntable that is wider than 19" in the UK requires a support system to be custom ordered for it to be wall mounted. The wall mount solution was not one which I was comfortable with for 2 reasons, the first being the weight of the deck which was in excess of 60 lbs. The second being the wall strength, as my extension is constructed using stud construction and the stud centres are not the correct distance to act as secure mounting points for a wall mounted support system. The idea of having a support custom built was sunk completely by quotes of over 400 UKP from a couple of support manufacturers and neither of these would deliver the level of isolation I was looking for. A further point was my desire to use a sandbox type system as I've heard these used on floating sub-chassis turntables to great effect.
After looking at my main requirements then I decided that whatever I used would have to meet the following criteria
1. It had to be floor mounted on spikes.
2. It had to use a sandbox and the deck was to sit on the sandbox
3. It had to bring the deck to a normal operating height (for me 36" off the ground)
4. It had to be fairly cheap (as I'd spent most of my money on the deck)
Taking these factors into account and after toying with a few ideas I hit upon the idea of building a sandbox bigger than anything so far commercially available. Built about the size of a coffee table it would bring the deck to just the right height, would be practically unmoveable due to it's extremely high mass and as such would offer excellent protection against footfall and floor transmitted vibration. As a home built design it would also be cheap!
Having now refined my idea in my head dimensions and practical construction had to be considered. The deck which had caused me to go to these lengths was a recently acquired, used Basis Gold Debut Standard MK.1 / Graham arm / Benz Glider cart. This deck is of similar size to a SME model 30 of VPI TNT IV, but you can manipulate the construction described below to any size of deck. But I'd go for something a little larger than you need for the sake of the extra mass and you'll then have extra room for your next upgrade.
I decided to add to the basic idea of a huge sandbox on spikes a low level shelf under the main box. This was to house the phono stage, so I could use a shorter length of phono cable and the very delicate MC signals (less than 0.1 mV) have to travel as short a distance as possible. The T/T power supply would have somewhere to sit which was out of the way but still convenient to get to if needed. The eventual design had a box that was 36" wide, 24" high and 28" deep mounted on legs which would lift the base of the box a further 8" off the ground. This 8" clearance under the box would give me room to add a shelf to hold the phono stage and power supplies. The top plate was to be granite (though you could use marble or toughened glass) so without sand the box would be supporting over 100 lbs. The box, therefore, had to be extremely strong, as it would take nearly 600 lbs. of sand to fill the box!
Well, that's the philosophy of the design out of the way, let's start building the Sand Table.

DANGER WILL ROBINSON!!!

Before I get going a quick word of warning, this unit uses MDF for it's construction. Now MDF is glued together and when the glue gets hot (like when being power sanded or cut by a jigsaw) then it gives of a gas and very fine dust, which are both highly toxic. If you are going to user power tools to cut or sand this stuff please wear some kind of dust mask to keep out these particles. If you do not posses the necessary protective apparatus then either get it before starting or get your local timber merchants to cut the MDF for you. Now on with the show!

Tool Kit Required

Jigsaw
Power Sander
Electric Screwdriver
8 G cramps
Hammer
Approx. 100 small tacks ½" long
Very strong wood glue (I use the white PVA wood glue but you probably have your own favourite). 8 - 10 fl oz.

Construction Details

All details relate to a table the size of mine (36" deep X 36" long X 24" wide) but you can adjust the dimensions to suit your requirements.
1. First off we need to cut the panels we are going to use for the main box structure out of the MDF (don't forget the dust mask!). The side panels are 36" long X 28" deep and you'll need a couple of these. The end panels are 24" long X 28" deep. Naturally you'll need two of these also. You will now have four panels, which make up the four sides of your box.
2. Now at this stage I brought the legs into play, which I made out of 1 1/2" square wood batons. This was not the ideal choice. I'd recommend at least 2" square batons due to the weight involved. These batons need to be 2" shorter than the total height of the box i.e. mine are 34" long for a 36" high box. I cut mine about 1/8" too long and then sanded them all down to size with the power sander to ensure they were exactly the right length.
3. Now you have a choice to make. You can either nail the MDF panels to the legs (the wood batons) or you can use dowel pegs to build the MDF box and then screw the legs to the box. I cheated and nailed the MDF to the batons with a lot of small tacks, which I then filled over and sanded down. My cabinet making skills were not up to using dowel and precisely drilling the holes but it would probably give a more solid construction.
4. Now at this point you could really do with cutting the inside corner of each leg so all of the legs have a flat face, which faces the diagonal opposite corner. This is to allow you to fix a supplemental support if you are not having a lower shelf or a support to the leg to hold a lower table for the PSU etc. Only sand down or cut the lower part of the leg and make sure the sanded face finishes before the bottom of the MDF box section.
You should now have a free-standing box made out of MDF with four wooden legs on it.
5. Now you need to put a bottom on the box. This is where the G clamps come in. You now need to cut 3 pieces of MDF 35.5" long by 23.5" wide. These 3 pieces need joining together VERY securely. You cannot over secure these panels, as this panel will be taking over 800 lbs. of weight, if the box is as large as mine. Once you've glued these panels together and left them to dry thoroughly (24 hours should do it) you should have a single panel 2 1/4" thick and rather heavy. Don't be afraid to put a few tacks or nails through these panels for good measure just to be sure they're stuck together properly! Now trim the four corners so they'll slide down the four legs and sit inside the bottom of the MDF box. You'll find that this easier if the box is on it's side! I cut out too little material from the corners and power sanded them to fit. Try to keep the fit tight so you won't need much sealant to seal the bottom of the box.
6. Now screw four batons inside the box. This can be achieved either by screwing into the sides of the box or you can screw at an angle into the legs. These batons will take a lot of weight on them so make sure they are very secure! Now screw through the batons into the base plate. To be absolutely sure you can, if you wish, nail through the base plate into the batons for good measure with some small nails. I cannot stress strongly enough how you must ensure that this base plate is fixed in such a way that it will happily let you stand on it without even deflecting. Deborah (my very tolerant wife) and I actually stood in the box on the base plate to ensure it was strong enough.
7. You should now have a box on legs with a bevel on the inside of the legs. Now would be a good time to fit the lower shelf (if you're using one). I just cut some small pieces of wood, which were basically a 3" equilateral triangle. I then drilled 2 holes through the base of the triangle at a 90 degree angle to each other, then screwed then into place with the lower shelf on one side of the triangle and the leg on the other. Please see figure 1 for a view of the lower shelf being held by the triangular supports.
8. Now grab a tube of silicone sealant and go mad in the box. Basically wherever there is a joint blast it with the sealant. Sand will seep through even the smallest gaps in the panels (my Hoover spent a good couple of hours paying the price for me not knowing this at the time) so take your time and don't spare the silicone! You can see how thorough I had to be with the silicone sealant in figure 2.Now leave this to dry and take a look next day to see if there are any panel gaps. If there are give it another blast of sealant, if not then pat yourself on the back for a job well done and turn the box over (get some help with moving the box, it will be very heavy by now) for the last part of construction, the fixing of the spikes.
9. In my listening room the floor is carpet - underlay - 3/4" MDF - 12" thick poured concrete :-) This means that the carpet piercing spikes also pierced the underlay, the MDF and buried themselves into the concrete. If you have a polished wooden floor then spikes are not the way to go. Also if you are on a suspended floor please check that the area under the T/T box is very secure i.e. on a load-bearing member. If not now is a good time to think of reinforcing the floor. I now fixed the adjustable spikes to my box, which came in 2 sections. The plate with a thread on it was sunk into the leg (I first drilled the leg and kept using a bigger and bigger bit until I could get a Dremel circular sanding attachment into the holes and expanded it out to the size I wanted). Now onto the upturned thread I screwed the spike. For more conventional spikes you'll want to drill into the leg with a bit slightly wider in diameter than the diameter of the spike. Now drill a wider diameter hole in the bottom of the leg into which you should glue a nut of a suitable thread to screw onto the thread of the spike. You can now screw the spike into and out of the leg to get it level. The fixing of the spikes can be seen clearly in figure 3.
Now all that remains is to sand the box down with 1000 grade wet and dry (by hand to get the optimum finish) and then seal it with a wood sealant.
It is now ready for painting. I used an acrylic aerosol paint (from a car parts stockist) to spray the box and then used an acrylic lacquer to seal it. It took me four coats of each to get a decent finish but someone who knows what they are doing could have got a much better finish then I managed to achieve. Now position the box in it's final position. This is essential, as this table will be unmoveable once it has sand in it. Once it is exactly where you want it you can start filling it with sand. I used some kiln-dried sand from a builder's merchant. The sand has to be totally dry and salt free so sand from a beach is definitely a no go area. My box took 11 55 LB bags to fill it up to 3/4 of an inch of the top plate. Try to ensure that when you're filling the box that it is poured in evenly over the entire base plate and check to ensure there are no leaks anywhere. Now continue pouring, levelling and pouring again until the box is full to within 3/4" of the top.
Remember how the legs were 2 inches shorter than the total height of the box? Well that is so the top 2" of the box hasn't got any of the legs in the way and to ensure that the top plate only makes contact with the sand, not the legs which might transmit vibrations through the spikes, into the legs and straight into the top plate wasting all of your efforts to build a box full of sand! You can clearly see the shorter legs here in figure 4.
Ensure that the legs are covered with sand and make the sand as even as possible and as flat as possible. Now put on your top plate. I had a local stone mason cut a piece of Granite for me 1/2" smaller than the inside dimensions of the box so there is about 1/4 of an inch around the top plate where sand is visible. It is vital that no part of the top plate touches the sides or the legs, only the sand. Any contact between the top plate and any part of the box structure will totally compromise the design! Also, DO NOT UNDER ANY CIRCUMSTANCES USE MDF AS A TOP PLATE MATERIAL!!! The sand will settle a little and the MDF just warps and throws out your entire T/T suspension, which completely defeats the object of the exercise. Trust me Granite is not only dense but it looks sensational when it is polished and bevelled. Here is a picture (figure 5) of my completed Sand table in situ awaiting the Basis to be installed on top of it.
If everything has gone right to this point you now have a box 36" long X 36" deep X 24" wide which probably weighs about 700 lbs., is on 4 spikes and whose top plate is totally isolated from the outside world. You have completed construction of a Sand Table.
Like I said I just took the idea of a sand box to it's ultimate conclusion and I feel it should be able to go up against these air platform bases in terms of isolation from outside vibrations. It is also utterly inert so it should protect your T/T as well. The finishing touch for mine will be a cover made of 1/4 " thick clear acrylic (i.e. Perspex) which will fit around the outside edge of my top plate and provide me with a T/T cover for my Basis when it's not in use. A friend of mine is in the glass trade so he'll be making one up for me (the Basis's piano black finish it a dust attractor so you NEED a cover like this to keep it looking it's best). See here for the completed installation minus the lid.
How does this perform you ask, well I've only used the Basis Gold Debut on the Sand Table, but to give you an idea of the level of isolation available, I rapped the side of the support directly very hard and the deck's suspension didn't even move. In terms of sonic performance, as I've not used any other support with this deck in this room, direct comparison is impossible. I can state that in the last 16 months I've been using the Basis on the Sand Table it has not once given me any indication of any sort of breakthrough or noise being transmitted to the deck from the actual environment. To me this represents a success.
At the end of the day for the 100 and something UKP this entire project cost me I do not believe that I could have purchased a T/T support which could have given me this kind of performance on a deck this size for so little money. So as a value for money exercise it has been a total success. As an aside the black Sand Table with the piano black deck on top looks great. Obviously you do not need to make it as big as mine but for the larger decks, which seem to proliferate from the USA then this might be a good solution for a cost-effective support.


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