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!
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