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Old 29th March 2010, 07:01 AM   #11
lowpoke is offline lowpoke  Australia
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Wood.

Or have you thought about bamboo? Seriously ... I've been impressed by this Lenco plinth fashioned from a bamboo chopping board! Owner says it sounds amazing.

Click the image to open in full size.

Click the image to open in full size.
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Old 29th March 2010, 05:55 PM   #12
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Binspaul, the answer to your question depends on a number of things. What is the deck, how will it be attached, what is the arm, how will that be attached, what will it sit on, and what type of sound do you like. There is no universal correct answer, lots of factors contribute to the overall sound.
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Old 30th March 2010, 02:06 AM   #13
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Old 30th March 2010, 05:08 AM   #14
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Hi,

> The turntable is a custom made one with acrylic platter. It is also having a thick sub-platter made of solid wood.
> The player is driven by an AC synchronous motor from Premotec.
> The belt is 1mm surgical silk thread.
> The tonearm is a DIY Schroeder reference model.

What I am planning to build is a layered model with 3 layers of wood, each having a thin layer of acrylic/cork between them (Wood-Cork-Wood-Acrylic-Wood). The motor will be completely isolated from the main board to remove the vibrations from getting transmitted. The whole assembly sits on a solid granite/marble block.

1. What is the best medium for making the platter mats - Felt, Cork, Leather, Rubber ... ?
2. Which is the best position for the motor - Back (Normal Players) or Front (DPS Turntable) ? What benefit does we gain if we move the motor to the 7-o clock position ? Please suggest...

Best regards,
Bins.


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Originally Posted by sq225917 View Post
Binspaul, the answer to your question depends on a number of things. What is the deck, how will it be attached, what is the arm, how will that be attached, what will it sit on, and what type of sound do you like. There is no universal correct answer, lots of factors contribute to the overall sound.
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Old 30th March 2010, 03:28 PM   #15
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There's no correct answers here, otherwise all decks would be the same. If you motor is standalone then put it wherever you like, the further away from the cartridge the better.

On suspended decks where the motor is separated from the main bearing and the belt will pull the suspended elements of the deck then there is some reasoning to lining up the motor pulley, main bearing and tonearm bearing in one straight line- 7 O'clock. But this depends on suspension compliance and ability of motor to load the suspension.

Try different platter materials, they all either damp- rubber, silicone, cork, felt, or couple, acrylic, copper etc, the ratio of damping to coupling varies with material as does the speed of energy transmission through the medium. It's also worth considering the effects of reflection from the stylus and how they differ with platter material and surface area contact. You could even float the record in the middle for minimal platter contact, several manufacturers have used a variety of lines, dots, slices and circles over the years to do this.
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Old 31st March 2010, 05:03 AM   #16
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Hi,

Great tip and will definitely try out.

Best regards,
Bins.

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You could even float the record in the middle for minimal platter contact, several manufacturers have used a variety of lines, dots, slices and circles over the years to do this.
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Old 20th April 2010, 10:29 PM   #17
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I am building one up now, and have done a lot of research on the subject (probably too much at this point ), and as a former custom guitar builder, have a reasonable amount of experience with wood as well as carbon fiber laminates and many metals.

To keep it short and on topic (which failed as you can see by the length ), I am using three materials for my plinth. For the very top and bottom 'layers' I am using standard Baltic Birch Ply; ~16mm thickness. Inboard of this on each side, I have 3/4" MDF which has been bonded with wood glue. At the very center of the 'sandwich' I have acrylic sheet (1/4"). So it's (from top to bottom) Birch ply / MDF / Lexan / MDF / Birch Ply. I may epoxy the lexan, or I may bolt the sandwich together to reduce the coupling of the materials (and make servicing easier).

Wood is fantastic stuff, and has been used in Plinths for a long time. No two pieces sound exactly alike (not even from the same log) It tends to be 'warm' sounding (but not always), and can be quite resonant. The more 'joints' it has (i.e. laminations and/or butcher block gluing) the more the sound waves are broken up and either dissipate or the harmonics cancel each other out. A butcher block sounds more like a chunk of concrete than like a solid wood board of similar size and species. This is why my neck-through guitar designs have one piece of wood (well, longitudinally laminated vertical grain actually) from the nut to the bridge, to complete the 'harmonic circuit' ("Harmonic Circuit" is a term I use by the way, so no one else may have used that particular term before) with the string above. Resonance and sustain are VERY long this way. Compared to a Gibson (known for sustain) with it's glued-on neck, there is no comparison really. The glue line ACROSS the 'harmonic circuit' in the case of the Gibson causes some of the harmonics to die due to reflection off this glue line. Alembic uses a similar method as I do (or rather I do it like them- they did it first!). Bolt-on Fender designs are of course worse in this regard with even less coupling than glued-on necks (although we press-fit our bolt on necks and they were not too bad for a bolt-on...)

Take a piece of string and stretch and pluck it. Now cut the string, tie it in a knot and stretch it the same way (pitch at length). Notice how the vibrations die sooner?

So, using multiple materials can be advantageous, but bear in mind the sound you want at the end at all times. Hard plastics, glass, metals and rock (i.e. granite) tend to be bright; with soft materials (cork etc.) tend to be more 'dead' (concrete tends to be dead too). Do the 'wrap' test and see if you like the tone of a piece of material before you use it. If you want dead, make sure the tone dies quickly. Rosewood, Cocobolo, ebony etc. can resonate for a LONG time (used for Marimba bars), whereas MDF dies more quickly- but about the same rate as Birch ply if you listen carefully to similar sized pieces suspended at their nodes. MDF is not as 'dead' as some think; just different.

So, if you have an overly bright cartridge/tonearm, go for wood/MDF to balance the sound. Like a bright guitar might go for pure nickel strings rather than stainless to take it down a notch. You have to think about the entire system. A glass platen on an MDF plinth with a laminate surface (A la REGA) is a pretty good sounding combination, because the balance is there.

I went with what I did to get the warmth of the wood (and the nice grain for a finish later- note the finish chosen can affect sound as well!) with the stability of the MDF. The glue line(s) do a lot to dampen errant resonances in the stack. If the frequency is too low (solid MDF) it COULD cause more rumble, or at least allow it to continue. Probably not, but anyway... Coupled with the somewhat brighter ply and lexan, it seems (to my ear) to be a better mid range balanced pile of material. Until it is finally glued up and has a finish on it, I won't truly know (so it has to at least LOOK good), but the resonance it DOES have now is quite short lived, which should prevent building harmonics that can cause feedback in a worst case scenario.

Motor should be as far as possible from the cartridge; in line as stated for the reason stated. I have no idea exactly where mine will be yet- probably inside one of the legs (I am belt-driving the OD of the platen directly for the torque advantage) around 10:30 position.

Another thing often regarded as an afterthought is the bearing itself. Is it able to carry the weight of the platen you have in mind? Overloading it can cause (or contribute to) rumble. Often a Teflon disc is used as a thrust pad; however I disagree with this line of thinking. I believe the 'pad' should be hard like the bearing itself (and have a very fine finish) to prevent any compression. If you form a 'pocket' with the ball (from all the weight on it), you increase the surface area, which increases drag (even on Teflon) and the possibility of rumble increases as well. I am hashing out design ideas for my bearing now, although my platen with not be as massive as the current trend seems to be (and conversely my bearing will be quite massive).

For my platen I am leaning toward Delrin with copper weight slugs at the perimeter at the moment; although PVC might be a better choice... Or a copper ring rather than slugs...

It is a simple machine, but because of its simplicity every detail must be carefully thought out to get a nice harmonious package when done! I believe this is a big reason why changing a tone arm can have such an impact. Not just the sound of the particular arm; but rather the way the entire machine is changed. Also why an arm can sound 'good' on one table and 'bad' on another. The arm didn't change now did it...

I equate it to a single-action revolver. Very simple, but when it is done well (such as USFA) it is just a true pleasure to shoot. Everything just WORKS. That is the goal for me. Simple, effective and good.
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Last edited by Jim Leach; 20th April 2010 at 10:32 PM.
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Old 21st April 2010, 01:27 AM   #18
lowpoke is offline lowpoke  Australia
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Nice post Jim! Very informative.
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Old 21st April 2010, 04:43 AM   #19
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Hi Jim,

Great post. I too am in the direction of using multiple layers...

Best regards,
Bins.
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Old 21st April 2010, 06:43 AM   #20
Nanook is offline Nanook  Canada
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Default second the bamboo...

I absolutely love mine (Sugden Connoisseur BD2, custom arm). The plinth is from a chopping block. Feet are wood. 3/4" aluminium square tubing separating the plinth pieces (see attached picture). Sounds way better than it should.
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