posted 09-13-1999 05:43 AM            

If anyone can help me out with advice on wiring, motor and other parts to use, and where I can get these I'd really appreciate it.

posted 09-13-1999 05:14 PM            

I'm waxing on about this as I just had a class in turtable design and modifications.

posted 09-13-1999 11:29 PM            

quote:

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I'm waxing on about this as I just had a class in turtable design and modifications.

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OK, Susie Q. 'Fess up. All the gory details, please.

posted 09-14-1999 02:26 PM            

The class was in preparation for the new Merrill Turntable which should be ready by the 1st of the new year, if all goes according to plan. We huddled in the bowels of Underground sound for the better part of a day and came away with a pretty clear understanding of the physics of turntables.

Of course the function of a turntable is very simple: to allow the stylus to vibrate in the grooves of the record without having anything else vibrate in the audio band, thus muddying the sound. We talked extensively about the problems with the original AR-XA and to varying degrees, many of the same problems extend to the Linn, the Pink Triangle (that I had) the Garrard and every spring suspended turntable ever built.

The AR, of course, was an inexpensive turntable whose main drawback is an aluminum subchasis. They have fairly small springs which don't do the best job in damping audio band energy. That energy is tranferred to the aluminum platter which passes it to the stylus.

Well-designed springs will dampen a vast majority of the upper frequency energy that they encounter, but pass the low-frequency energy into the subchasis (causing footfall problems with shaky floors). Using a subchasis made of a very rigid arcylic with a very low resonant point will absorb a lot of the low energy frequency passed by the springs and also the audible energy than escapes the pass-through spring filter.

George also explained the philosphy behind his peripheral ring clamp which is to capture the rotating magnetic energy created when the stylus passes through the grooves. This energy radiates in both directions from the stylus. The periperhal ring clamp's main function is to absorb the magnetic energy raditating to the beginning of the record.
The old AR not only has an aluminum platter, but an aluminum subchassis and sheet metal top -- and they all vibrate.

We also discussed platter bearing mechanisms, the function of a highly viscious oil in creating an almost frictionless bearing, the use of arcrylic/lead combinations, particularly in the platter, where the thin lead coating creates the best bond possible between the vinyl and the arcrylic platter, which further serves the dampen energy and open soundstage.

We also looked at damping which is a function of mass, material density and material type. Arcrylics are dense and have a highly rigid molecular structure, but are somewhat lacking in mass. That's why the old Merrill base is made up of a sandwich of arcrylic/lead/arcrylic with a wood veneer on the outside for cosmetic purposes. Lead adds a lot of mass and extra damping.

I'm a believer in damping. I think I could drive a freight train through my living room and my Merrill wouldn't miss a beat. I couldn't even walk in the same room with the Pink Triangle and the Garrard has the same problem with footfalls.

All in all it was very enlightening. It made me rethink the function of the base/subschasis parts of a turntable. The design and material used would certainly influence the sound of the table and I would not look upon this design as trivial, but as one of the most important components of the turntable. I would personally rather have an ugly base than an ugly sound.

Cheers,

Susan

posted 09-14-1999 04:18 PM            

I'm not sure if one could use a regular saw on it however, but I would think you could have a saw and mitre job done to spec from folks who do custom kitchens. You can always overlay it with the veneer of your choice.

posted 09-15-1999 04:55 PM            

quote:

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As for the base - you suggested Corian - what other acrylics are used by turntable makers such as Walker and Clearaudio. I have some friends that can do AutoCAD and injection moulding - so we just need to figure out what the best material will be - the acrylic sounds ideal as it can be moulded.

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The vast majority of acrylic resins are manufactured by either DuPont (Corian) or Goodyear (they make the polycarbonate type). Merrill was the first to use arcrylic and I'm quite certain his is very closely related to Corian if not Corian. In fact, he benefited from the advice of an audiophile friend who just happened to be a chemist for E.I. DuPont. If I were doing this, I would seek the advice of one of the chemistry groups such as sci.chemistry and ask about what other arcrylic resins are similar to Corian and explain your application. It's highly unlikely an audio company developed a proprietary arcrylic resin on their own. DuPont has a Corian (Search Corian on any search engine) page on their website. Why don't you email them?

quote:

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And wiring between the cartridge and outputs - I'd also like to replace this, as well as the outputs - do you know brands that would be the best and where I can get hold of them?

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Wiring I would think would be the easiest of your problems as there are so many different types to choose from and I'm sure many opinions as well. I've heard a lot of postive comments about Cardas wire in tonearm applications.

quote:

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Oh yes, have you any idea about compressors? The one that came with the Maplenoll has expired - are there any small quiet compressors made specifically for turntables?

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I don't have any experience with turntable compressors, but it would be unlikely there is one specifically made for turntables. You can email the various parts houses and ask their advice. I have a smattering of listings at http://www.hifiheaven.com/electronics-parts.htm Newark Electronics has a 15,000 item catalog on-line. If you have a manufacturer number for your old compressor you can search on that number.

quote:

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We have access to quite hot designers, engineers and computer boffins - now we're thinking about putting together a snazzy turntable with an air bearing arm and floating platter - but at a reasonable
price to compare with entry level regas and linns. Any thoughts about this?

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Hey, I think it's great! I've been advocating resonably priced turntables for a long time. The biggest hurdle, I think, is getting it reviewed and marketing. Merrill is launching a new table which will be marketed on the internet exclusively. George thinks, and I agree with him, that specialty analog audio will become the provence of the net because of the small market. The net is the perfect way to reach this market at a reasonable cost.

Keep us advised of the progress. Why not make a webpage documenting the adventure? I'd be happy to publish it for you. You could take some before, during and after photos. Way cool!

Cheers,

Susan

posted 09-24-1999 12:24 PM            

Unfortunately, I don't have time to write a complete manual, but may be able to help in bits and pieces.

For starters, you can see the TT as a work in progress at http://www.laventure.net/tourist/good_sound_tt.htm. . The original has been completely deconstructed and the only remaining Maplenoll parts are the air bearing (modified as per Bruce Thigpen's suggestions and too complex to explain in 25 words or less) and the platter, a nominal 50 lb. upgrade from Maplenoll (now defunct). [Bruce was one of the original engineers who worked for Colonie, the predecessor of what became Maplenoll after Colonie was dissolved. He acquired the rights to their arm and went on to found Eminent Technology.]

As you can see, the Maplenoll arm has been replaced by an ET2 (now 2.5) and the plinth was rebuilt as a multi-layered sandwich with a 1/2 inch thick lead plate in the center. Other materials in the sandwich are EAR Isodamp, MDF, and Corian. The whole thing is bolted (not cemented) together on the principle that dissimilar materials will resonate at different frequencies which will cancel each other out.

The arm and motor are each mounted on a 25 lb. lead brick. The 50 lb. platter (which actually weighs 45 lbs.) is mounted on a 1/2 inch thick steel "pie plate." Copper tubes filled with lead shot are attached at the perimeter. The pie plate has a steel band welded onto it to accept the pully (from a VPI TNT) and the entire platter assembly weighs about 105 lbs. The idea is to keep the center of gravity in the same plane as the bearing and the pully. This makes for faster start-up and a smoother ride.

The motor is a high torque Hurst model RA-3915-001 www.hurstmfg.com/sync_motors/specs_ra.html which gets the whole thing up to speed in under 10 seconds with no manual assist. BTW, the pully has a slightly oversized diameter and the motor is plugged into a VPI PLC (next to the latest model) set at 51Hz. This increases the torque and helps to reduce line noise (VPI does this in their own TT's).

The air compressor is situated in a remote location and is a Thomas 100psi industrial strength model. The air from it passes through a separator (to remove condensation), a 12 gal. surge tank (to smooth out the pulsations), 50 feet of Tygon tubing to another 4 gal. surge tank located near the TT, a couple of filters to remove minute particulates plus any remaining moisture, and a couple of Fairchild regulators (one for the arm, one for the bearing). Whew!

Since the cut-away photo was taken, the plinth and motor mount have been finished in cherry wood to match the custom stand (which includes a sandbox topped with a slab of Corian built into the top). The original pie plate has been replaced with one that is not as wide and the entire platter assembly has been spray painted semi-gloss black. [Updated color photo of the finished project coming soon.]

The whole thing was done in stages over several years, in the course of which the Athena disappeared and the "Stealth" (as Susan has referred to it) emerged.

The final result is dead quiet. By which I mean that LP's sound as quiet as CD's and every improvement has yielded an audibly positive result.

Was it worth it? Well, this began as a simple project and if I had known how much time (months when added up) and money (perhaps $4,000) were involved, I probably would have bought an Immedia, a Clearaudio, or a TNT. However, I've learned a lot and now have a world class TT which I think could go head-to-head with the best (Rockport, Goldmind, SME) and hold it's own.

Any questions, Class?

-J-

BTW, except for the Fairchild regulators, most of the air compression system was sourced from Grainger, a nation-wide supplier of industrial materials www.grainger.com/ .

The lead plate came from McMaster-Carr www.mcmaster.com/. RCA jacks are WBT NextGen Ag,
the EAR Isodamp came from Michael Percy Audio Michael Percy Audio, and the MDF, Corian, copper and steel were purchased locally.

Finally, I couldn't have done it without the help of Phil Fisher, a retired machinist who made vacuum tubes during WWII at GE, and Jay Victor, an air compression engineer, who is now the New Products Development Manager at Monster Cable.

[This message has been edited by Joseph Levy (edited 09-24-99).]

[This message has been edited by Joseph Levy (edited 09-24-99).]

[This message has been edited by Joseph Levy (edited 09-25-99).]

posted 09-26-1999 04:00 AM            

Many thanks for the detailed reply. You've managed to build yourself a really wicked TT - it must produce a really fine sound. Why did you decide to do the rebuild in the first place?

I've got a million questions - but perhaps first what was Bruce Thigpen's suggestions to upgrade the air bearing?

Cheers
Jonathan

posted 09-27-1999 11:54 PM            

The whole rebuild project basically started because the Maplenoll was so easy to deconstruct and had so much (at the time) unfulfilled potential -- the lead platter, the air bearings, and so on. But the thing needed so much tweeking that it just invited modification. It also began with my frustration with the Maplenoll arm (an ET1), which was impossible to keep properly set up and the project grew from there. Replacing the arm with an ET2 was the first major modification (and an easy one).

Re: Bruce's mods to the air bearing. The problem with the original bearing is that the air comes in from just one large port. This is why Enid Lumley goes to great lengths to explain how to dynamically balance the platter in her articles on optimizing the Athena (The Absolute Sound, issues 48-51). This was necessitated by the uneven elevation caused by having just the one air hole. To clarify this somewhat, think of the compressed air emanating from just one large port and elevating the upper bearing plate. Obviously, the air entering from that port would cause the plate to be slightly higher at that point and throw the platter somewhat out of balance.

Bruce explained that the principle behind the multiple-concentric nozzle ports on the ET2 arm should have been applied to the platter bearing, too, but wasn't done in order to save money. In a nutshell, this means setting up six nozzles in a circle, each with an effective diameter of 1/1000th of an inch. The compressed air fills a well beneath the lower plate, then passes through the small-apertured ports and elevates the upper plate in an even circular pattern. Because the platter is evenly lifted, the need for dynamic balancing is eliminated. The result is that the platter turns with much less friction and requires less air pressure to be elevated in the first place. (Bruce went into greater detail about the physics behind the pressure differential above and below the bearing plate, but it's not really necessary to understand that here).

Anyway, to implement this idea, first fill or seal the existing port in the lower bearing plate. To do this, you'll need to remove the hose barb and fill the hole with a hex-head machine screw or epoxy or both.

Then drill six holes evenly spaced (60 degrees apart) in a circle drawn midway between the center and outer edge of the lower bearing plate (you'll need a drill press to do this properly). Each hole should be about .007 inch in diameter (that's 7/1000th's). Each is then tapped with a 6-32 thread tap. The threaded holes are then filled with 6-32 hex-head machine screws (or set screws) that are slightly shorter than the thickness of the bearing plate (say, 3/8 inch) and who's outer threads have been very slightly filed down. Ideally the machine screws should be put on a lathe and the outer threads shaved about .001 inch.

Because the threads were machined down slightly, when the screws are inserted into the holes, there will be a 1/1000th of a inch spiral passage for the compressed air to travel through in order to elevate the upper bearing and the platter which it supports.

Remember, you'll also need to create a circular well beneath the lower platter from which the compressed air is drawn. It only has to be 1/4 to 1/2 inch deep and slightly larger in diameter than the diameter of the circle on which the nozzles sit. The idea is that instead of air being fed to the bearing through a single port, the port now feeds the well which, in turn, provides a reservoir of air that is forced through the six (new) nozzles. This, in turn, elevates the platter.

Got it? [It's easier to draw a picture, but reread this a few times and it should make sense.]

Also, the lower bearing was originally held in place on the plinth by two long machine screws or threaded rods. This tends to warp the plate by exerting pressure across the diameter. Ideally, the plate should be held by three or four screws evenly spaced near the perimeter to eliminate this problem [this was done in later versions] and requires tapping two more holes for that purpose.

-J-

[This message has been edited by Joseph Levy (edited 09-28-99).]

posted 09-28-1999 01:48 PM            

Thanks again for the detailed reply. My motivation for rebuilding the TT is quite similar to yours – it’s a pretty nice sounding machine as it was – but has great potential to be an excellent TT. I’ve always liked the TT because it is such a simple design – quite elegant and a sensible approach to obtaining the best sound – and I thought it was quite a cost-effective way for regular people to get excellent sound.

I gather from your note that the arm which I have in my TT now (essentially a single block with single air hole) is an ET1. What problems did you experience with the arm? I actually contacted the ET group and the reply I received from Bruce was “To my knowledge the ET-2.5 does not work on many Mapleknolls. The Mapleknolls were built with there own tonearms and some models used a different layout than that used by the ET-2/2.5. These are really two entirely different products and the component parts are not interchangeable”. But I gather from your note that the ET arm can be fitted. I’ve had a look at the arm and can’t see any reason why it can’t be fitted.

I’ve actually thought about the lack of symmetry in terms of both the arm and air bearing air holes – something I used to ponder while listening to Pink Floyd in the dark and imagining I could hear all sorts of imperfections due to the asymmetry! Pure madness!

Anyway I am sitting here with my deconstructed bearing. I understand about filling and redrilling the airholes – no problem. I like the idea around the well beneath the lower bearing plate – makes great sense – but how did you actually create this well? Let me describe what the facing sides of my air bearing plates look like – it may be different from yours. Each plate has a slight, say 1/8 inch, depression occupying the centre half of the plate – does your machine have a similar depression – on the lower plate the air hole is about halfway between the centre and edge of the depression – about 1 inch from the centre. In the centre of the lower plate there is a small brass depression to accommodate a spindle attached to the upper plate. If I drill the six holes as you suggest from halfway between the centre and edge of the lower bearing plate they’ll actually fall right on the edge of the depression.

I’m wondering if it might be the easiest to completely remachine the air bearing, keeping the upper plate as is, but modifying the lower plate extensively along the lines you suggested. But perhaps the lower plate could be made about twice as thick as present, and a wide air well, as you describe with the six holes, cut into the bottom and the walls threaded – then a threaded well cap could be made to be screwed into the well – the cap would have a port for incoming air. Would this be a more desirable approach to simply welding on a plate to seal the well? If machining is a desirable option, then what would the best material be to use for the air bearing?

On a completely different note – your plinth – what made you decide on the materials and different widths and order of materials? If you had to do it over, would you choose other materials?

Cheers
Jonathan

[This message has been edited by Jonathan (edited 09-28-99).]

[This message has been edited by Jonathan (edited 09-28-99).]

posted 09-29-1999 11:25 AM            

quote:

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I gather from your note that the arm which I have in my TT now... is an
ET1. What problems did you experience with the arm? I actually contacted the
ET group and the reply I received from Bruce was "To my knowledge the ET-2.5
does not work on many Mapleknolls."

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Bruce is right about the arms being different products which no longer share any
parts. But there's no reason why you can't completely remove the ET1 supplied
with the Maplenoll and replace it with an ET2-2.5 -- you just need to use the ET
set-up jig (or be very exacting about mounting it in the right spot on the plinth). To
that extent, they're not exact replacements.

The real problem with the Maplenoll arm is nearly impossible VTA adjustment
and the sloppy way the arm block is attached to the plinth. All parameters need to
be checked every few weeks to make sure they are tight. Also, the ET-type arms
perform better at 10-14 psi, far higher than the flow from either original
compressor.

BTW, Jay Victor (mentioned above) has an unmodified original Athena (with an
upgraded air compression system, as mentioned above) that performs flawlessly.
It's just a matter of getting the setup right and keeping it that way.

quote:

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how did you actually create this well?

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It's fairly easy -- if you rebuild the plinth, you can incorporate it into the top of
new one. If your new plinth has a top composed of, say, 1/4 inch thick Corian,
just cut a circle with the required diameter (perhaps 5 or 6 inches) and make sure
to mount it directly on top of a solid layer. The circle you've cut represents the
volume of the well; the layer underneath is the bottom of the well; the underside of
the lower bearing plate is the top. Ideally, the air hose or port should feed into the
exact center of the reservoir.

quote:

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Let me describe what the facing sides of my air bearing plates look
like... If I drill the six holes as you suggest from halfway between the centre and
edge of the lower bearing plate they'll actually fall right on the edge of the
depression.

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Your bearing seems to be identical to mine. The new circle of air ports do not
have to be in the exact center -- that's only an ideal. A half inch (or more) either
way should have little or no effect.

quote:

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I’m wondering if it might be the easiest to completely remachine the air
bearing, keeping the upper plate as is...

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With an eye towards manufacturing my own air bearing TT dedicated to the ET2
arm, I had the exact discussion with Bruce T. The bottom line is that it's
completely uneconomical. The bearings were machined from an exotic alloy to
extremely fine tolerances. Bruce said that for every 1000 pieces, 400 would have
to be discarded because they did not meet the specified tolerance. And you need
at least 1000 pieces to begin with.

If you set things up properly, the lower bearing plate, the top plinth plate, and the
next plate down from the top (all of which constitute the air reservoir) can be held
together mechanically using machine screws. A bead of sealant (silicone, for
example) should be run along the edges to help prevent air leaks.

quote:

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what made you decide on the materials and different widths and order
of materials [for the plinth]? If you had to do it over, would you choose other
materials?

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The materials were chosen because they are all considered to be acoustically
"dead." That is, they have no real audible resonance. The use of lead in both the
plinth and the platter is really the key ingredient and is one reason why the
Maplenoll is such a good performer despite it's shortcomings. The air bearings in
the arm and platter, combined with the radial tracking arm itself, is another.

The actual order of the materials (as well as their selection) was somewhat
arbitrary. It made sense to put the lead plate in the core and let the Corian do
double duty as the veneer. MDF is commonly used in the best (and deadest)
speaker cabinets and the EAR material could also be replaced by Masonite or
some other dense insulator. The important thing, as Jay pointed out, is that all of
the materials have different densities and resonate at different frequencies. By
bolting them together very tightly, these characteristics tend to cancel each other
out.

-J-

posted 09-30-1999 11:07 PM            

I noticed from your e-mail address that you're located in South Africa. It must have cost a small fortune to ship the Maplenoll over there!

Since many of the sources I mentioned (above) are in the USA, I'm not sure how useful they are to you. [Surely, there must be someplace closer than New Jersey for you to procure a lead plate.]

Anyway, I recently purchased a second junked Athena (missing it's arm) plus another ET2, with an eye to seeing how easily the basic TT could be transformed into something greater (and for a reasonable price!).

It may be a while (months) before I get into this one, but I'll keep you posted on my progress from time to time.

Regards,
Joe

All times are ET (US)