Turntable - The Empirical

Design Outline and some Photos

 

 

 

 

 

 

 

Peter F. Kelly

To my knowledge, this is the only triaial air-bearing table in existence.

The design work is first and the construction photos follow.

Lastly, don't forget to enjoy the music and have fun!

 

 



Subject: Turntable, Platter, Plinth, Armboard, Feet, Bearings, Tonearm, Pneumatic Power, Electronics, Motor, Electric Power, Base

Object: Make an analog turntable to match proportionate quality of existing designed constructed Stereo, which is modular and serviceable.

Designed: February 21, 2004, staged design throughout construction


Constructed: March 2, 2004 - October 3, 2004

Research Organized: October 3, 2004 - November 25, 2004
 

The EMPIRICAL

Platter
The platter weighs 41.5 lbs.
Pure 1" lead contacts the record.
The lead is damped by resting on a constrained layer of 3/16" sorbothane 40 (Shore 00) durometer.
The lead is a doughnut-shape and rests in cast and machined methyl methylacrylate (clear acrylic).
A vertical precision acrylic insert is fitted for the vertical steel air bearing shaft snug fit.
The record spindle is concentric with the shaft and isolated in the acrylic.
The record spindle has a 17/64" sleeve and can be removed for further isolation.
A clamp above and washer below bring the record into total contact with the lead surface.
A white ready-to-transfer plastic strobe is applied to the bottom surface of the platter acrylic.


Plinth

The plinth has an isolated tonearm board.
The plinth has four separated legs with nonadjustable feet.
The plinth is from a wood superstructure. Wood has the ease of the manipulation and beauty. It is used as an acoustic dissipater and a splint to hold dampening material.

The wood is Acacia Koa. Koa has a unique grain and iridescence giving the grain a "cats eye" gemlike appearance changing with the angle of view. It is fluorescent under ultraviolet light. The tree is rare and protected by law. It is endogenous only to Hawaii and only fallen trees can be harvested. Frequently used in to guitar soundboards, this medium density hardwood is difficult to cut due to its growth in heavily mineralized volcanic soil.

The feet and armboard are connected to the plinth via nonmagnetic brass bolts, washers and locking nuts with zinc-coated brass spacers.
Each area of contact with the leg and the armboard contains a large dampening module.
There is a module filling the entire leg and entire armboard.
In these modules:
- are a tar/sand mix and have a durometer of about 10, a time-proven acoustically dead combo,
- are enclosed in Saran wrap, thus are removable for servicing,
- the Koa wood is coated with polyurethane to prevent tar migration,
- the inserts are sealed on the bottom with a layer of lead shot and silicone
In addition, there are 28 more dampening modules in the plinth which are filled with no. 4 lead shot and silicone.
The feet and armboard are connected to the plinth via nonmagnetic brass bolts, washers and locking nuts with zinc-coated brass spacers.
The bottom is protected with a 1/16-inch clear polycarbonate sheet attached with brass screws
Three .078/.156 ID/OD inch air bearing supply hoses pass through the plinth internally via 7/32" aluminum pipe conduits and exit through brass grommets on the wood.

Armboard

The armboard is described from upper to lower layers
The first is Koa wood matching grain with plinth as this is cut from joined pieces of Koa lumber.
This is epoxy glued to two layers of pure solid lead.
The lead rests on, and is dampened by, 1/4 inch of Sorbothane 40 (Shore 00) and achieves the proper elevation.
This is secured to a hollowed Koa wood bottom which is filled with lead shot and tar of very low durometer.
Nylon bolts secure the lead/wood layer and also compress it against the Sorbothane.
The bottom Koa wood portion connects to the plinth with 5 quarter-inch brass bolts.
The bottom Koa portion is also screwed into the two adjacent feet to decrease LF resonances.
The .078/.156 ID/OD inch air bearing supply hose passes through the armboard internally via 7/32" aluminum pipe conduits and exit through brass grommets on the wood.

Feet

The feet footers in the plinth are carbon fiber reinforced nylon (Kevlar Hydlar Zf).
The feet are pure lead in direct contact with the Kevlar footers. The adjustable aspect is not used.
The lead is machined on top to avoid contact with the polycarbonate bottom cover of the plinth..
The lead bottom is machined to internally accommodate 1/4" Sorbothane 40 (Shore 00) durometer upon which the turntable rests.
Nonmagnetic screws secure the two adjacent feet to the armboard to stabilize the armboard from LF resonance.
The feet are aligned by 1/4" nylon bolts threaded into the Kevlar footers.

Bearings

There are three air bearings, a vertical and horizontal bearing for the platter, and the ET-II tonearm bearing

Vertical Bearing

The platter has a vertical cylindrical porous carbon air bearing 1.0008" diameter (+0.0002 - 0.0000)
This houses a precision vertical shaft of 440C stainless steel 1.0000" diameter (+0.0000 -0.0003) Rockwell "C" 10-16 RMS.
The vertical shaft is confirmed round and linear to 0.0001 inch throughout.
The vertical shaft is cryogenically treated.
The vertical bearing is potted in the Koa wood plinth with 700-vinyl ester (404) resin epoxy.
The shaft fly height is 0.0008 - 0.0010" (8-10 ten-thousands).

Horizontal Bearing

The 440C vertical shaft rests on a precision horizontal 440C steel disc.
The upper and lower surfaces of the horizontal disc are flat, parallel and perpendicular to the vertical bearing by 0.0001", with the bottom surface is finished at 10-16 rms.
The horizontal disc is cryogenically treated.
The disc floats on a horizontal porous carbon air bearing.

Horizontal Bearing Suspension

The bottom of the horizontal porous carbon air bearing pivots on one ball bearing.
This compensates for off angles from absolute vertical. The ball bearing does not turn.
The ball is a precision ceramic silicon-nitride 0.50000" (+0.00005", -0.00004") Grade 5 bearing, density 3.21 gm/cc.
The horizontal porous carbon air bearing has installed a PTFE Teflon insert.
The bearing, rests on the ceramic ball via its PTFE Teflon
The bottom bracket is clear acrylic is indented centrally and has a PTFE Teflon insert.
Thus, the ball is sandwiched between two Teflon inserts, one above and one below.
PTFE Teflon is self-lubricating. Silo-Kroil was nevertheless sparingly applied.
Surrounding the bearing on the bottom side of the plinth are 8 clear 1" acrylic rods tapped for 1/4" threads.
These rods are suspended within silicone adhesive within larger holes drilled into 1.5" deep in the plinth.
The bottom bracket acrylic is mounted with 8 nylon bolts threaded into the 8 clear threaded acrylic rods
This provides for leveling adjustment of the bottom bracket supporting the horizontal bearing, of which angulation errors are compensated by rotation the ceramic ball on the Teflon inserts.
This also allows adjustment of platter elevation.

Tonearm

The ET-II uses a traditional discrete setscrew orifice jet air bearing and a hollow aluminum shaft.

Tonearm

The tonearm is a modified ET-II
The ET-II uses a traditional discrete setscrew orifice jet air bearing and a hollow aluminum shaft.
The manifold runs a maximum of 15 psi, but is noisy above 6 psi.
The aluminum and magnesium armtubes have been replaced with a carbon fiber one.
The headshell is carbon fiber and is attached with 700-vinyl ester (404) resin epoxy.
The interior is damped with rubber cement and filled with lambs' wool.
A separate aluminum tube glued to the bottom of the armtube carries the lead in wires.

Pneumatic Power

Air pressure is supplied from a nitrogen tank having a moisture content less than 3 PPM.
The outlet is 100 psi via a Northern Brewer regulator.
Alternatively room air compression is provided by a 125 psi 6.6 SCFM compressor with 33 gal reservoir.
The intake is filtered.
The output filtered with Wilkerson 5 u particle filter followed by a Watts coalescing filter .008 PPM, 0.3 u.
This travels through 100 feet of 1/2" tubing.
The turntable input is regulated by a series of four Iron Force regulators, using upgraded +- 2 % gauges.
The four regulators independently control, air input, horizontal and vertical air bearings, and the tonearm.
Three .078/.156 ID/OD polyurethane inch air hoses supply hoses conduct pressure to the bearings.
The hoses pass through the plinth and armboard via 7/32" aluminum pipe conduits and exit through brass grommets on the wood.

Wire, Electronics, Head Amp

The wiring is two tightly twisted pairs of 41 gauge Teflon coated gold wire (75 u, 0.0055"), cryogenically treated.
The twisted pairs are balanced to ground and also have an independent ground.
The small diameter and dense twist of the wiring is such that 2.5 linear feet are reduced into 14 inches.
The wire travels through a shielded tube below the arm and hangs below the armtube.
The connections are soldered directly to the head amp, which is mounted on the plinth.

The head amp is a modified Black Cube modified as follows:
- The input circuit to the INA217 has been rewired to be a balanced input
- The op amps have been upgraded from SSM2017 to INA217, and
- From OPA2604 (dual) to two LM7171 mounted on a single-to-dual adapter board.
- Rectron Shottky fast recovery barrier type SR1001 replace stock diodes.
- The case has been damped with Dynamat.
- Assembly screws and added lockwashers are now electrically conductive.
- Battery power.

The head amp input is modified for balanced inputs with resistors and capacitors as follows:
- BC precision thin film BB0207 series resistors, and
- Panasonic ECQP(Z) series noninductive polypropylene film cap.
 

Motor

The motor is a Teres Reference motor (limited production Maxon RE25 25 mm Precious Metal Brushless CLL 10 watt, model 118743 which has been modified with sleeve bearings).
The electronics regulations design is by Manfred Huber integrated with the motor housing.
Motor modifications are:
- replacing all stock diodes with Rectron Shottky fast recovery barrier type SR1001
- metal case screws replaced with plastic screws,
- Sorbothane lining to canister interior,
- Sorbothane isolation of canister top plate from the cylinder proper,
- additional lead shot to fill base compartment completely,
- silicone dampening of all discrete electronic components vibrating adjacent to the motor,
- removal of tiptoes and application of sorbothane 40 (Shore 00) base.
The strobe is a thick plastic white applique to the bottom of the acrylic.

Electric Power - Motor and Head Amp

Powered by a SLAB battery and the Teres "Battery Unit" integral battery unit/charger.
Each SLAB has a 10,000 uf and 100 pf capacitors for noise and impedance matching.
CAT-5 twisted twin lead with independent shield for battery leads.
Ferrite attenuators on start and end of battery leads

Base

The base is a isolation and absorption design using constrained layers with suspension and leveling.
The Kevlar / Lead / Sorbothane feet contact a plywood wood shelf having leveling tiptoes for leveling.
This sits on a base of 2-inch grade B analytical bench of solid granite.
The granite rests on a constrained layer of Sorbothane durometer 40.
This rests on a Corion shelf sandwiching the sorbothane.
This is on a welded wrought iron frame, which currently sucks big-time at 5.9 Hz.

Materials Reference

Some lumber store on Maui, A-M Systems, Digi-Key, Electronic Surplus, Bruce Thigpen, Eminent Technology, Fastsigns, Grizzly Industrial, Industrial Plastic Supply, K&J Magnetics, Lowe's Hardware, McMaster-Carr, Michael Percy Audio, Motion Industries, New Way Precision and their machine shop, Northern Brewer, Redco Machine, Sorbothane engineers, Teres Audio, Teres Audio Board, True Value Hardware, U.S. Composites, Van Den Hul, Vulcan Lead machine and engineers, various physicists and audiophiles.

RESULT

Low mechanical background noise, high electronic noise rejection, low stylus-induced vinyl induction noise, and high-resolution reproduction.

PENDING WORK

Logos and lettering on RTA.
Do something about the iron frame.
Measure Q of turntable components' resonances.
Measure Q of vertical and horizontal tonearm/cartridge resonances
Cryogenic treatment of lead platter component.
Analysis of increasing turntable definition cannot be accomplished until construction of:
- Construction of gold balanced interconnects from preamp to equalizer, or
- Construction of nonmetal interconnects
Change base design to isolate Richter 6.0+ level vibration from sub-subwoofer.
Construct 60 psi tonearm with porous carbon air bearings, losing less gas.
Construct a moving capacitor cartridge from the MC-10. (C:\video\stereos\turntable\cartridge\new_cartridge_ideas\cantilevers)

My sincere thanks to all knowledgeable and unwitting participants,

Peter F. Kelly, DPM



Photographs in Chronological Order



Reduced engineering diagram, elevated view.


Reduced engineering diagram, view from above.

 
Two Koa wood boards joined and plinth is being cut. The wood is 2 inches thick.
This is my first wood joining of boards and scroll saw job, purchased for this project.


Wood oiled and simulated preassembly.


Plinth, bottom view: horizontal bearing suspension assembly.
Clear polycarbonate in foreground covers lead shot/silicone cover layer over the tar/sand dampeners.
Gold paint prevents migration of the dampening tar/sand into the wood.


Business section of the turntable.
Plinth, bottom view: the self-leveling horizontal bearing is in place on the H B acrylic suspension.
There is a little tissue there to prevent bearing damage during pretesting.
Actually, this area has ten sections of designed layers, but this is just a website for sharing fun.
All the polycarbonate covers are attached now.
Feet shown are the temporary feet.


Relationship of machined pure lead doughnut platter component to its acrylic platter housing.
Who says you can't shine up a little lead?
Seran wrap shown covering Sorbothane 40 durometer (Shore00) in housing.

 
Underside of acrylic platter component remachined with acrylic insert for vertical-bearing shaft slip-fit.


Armboard, upper layers, inverted.
Shows wood layer, two lead layers, threaded for nylon bolts


Plinth, top view: Armboard in place, vertical bearing shaft in place in the vertical bearing..
Note Lead and Sorbothane in armboard. Bottom wood of armboard is filled with lead shot and silicone.
Also showing nonmagnetic attachments to legs of plinth.


Application of strobe.


Cryogenic treatment of parts and wires with liquid nitrogen.


Arm installation.


Lead feet. Left is upper side. Right is bottom side.
Upper side shown to contact Kevlar in plinth allowing room for the dampening module polycarbonate covers.
Bottom side hollowed out for sorbothane inserts and nylon bolts.


Final armtube assembly involving dampening different frequency spectrums:
Application of these two essential components cannot be done sequentially.
This method stuffs lamb's wool while simultaneously applies an internal dampening coat of rubber cement.


Electrostatic oxidization of silver interconnects following cryogenic treatment.


Some modifications of the motor.


Atmospheric air compressor.


View of balanced independent 41-gauge gold lead-ins.
Rewired black cube is seen with upgraded op amps.
Plywood base is for leveling. Now rests on 156 lb. Granite, Sorbothane, and Corion.


Enclosure for gauges.
Here is the granite and Corion.


Digital camera fun. Macrophotograph of Colibri XGP.
I think this is 45 gauge wire.
 
 
- Kelly