I am pondering a new plinth design and am considering the virtues of making a skeletal or closed plinth design. The motor unit is direct drive. I know that as a direct drive it inherently has very low vibration as opposed to an idler deck (please do not outcry Garrard and Lenco onwners coz I have one of those too) but simple facts are facts belt drive motors spin at 250rpm, Lencos around 1500 rpm, DD 33 or 45 rpm. That being the case that must surely be a factor in this issue. What are your thoughts. BTW I like closed designs as they prevent the gathering of dust.
Parrotbee This is a tad unfair given that you don't know what I do do, and what else I have built and fiddled with.
Hi Parrotbee I didn't mean yourself when I said.
I used to say to myself ...hmmmm looks like a hole / space there. Wonder what would happen if I filled it ? When an audiophile based on theory alone, said don't do that, its not right because of xxxxxxx, but showed no real direct experience with it himself...... ..Hell..the more reason to go and do it.
I didn't even know of you up until last week ? Sorry for the confusion. I was referring to others in past dealings on this forum - like some of the debates on the Copernican thread.
It think it really goes back to my poker game analogy and cards showing. We would all benefit imo in knowing more about yourself/experiences being the OP but its your choice obviously.
fwiw - My cards are all showing. In fact if you have read the ET2 thread and my system thread you probably know some things about me that my wife doesn't even know.
The strangest/worst thing one can do is fill up a plinth with some type of permanent resin, and then be unable to remove it, or indeed sell the component due to the over-enthusiastic 'intervention/innovation'
I agree and Blue tac(k) is reversible. In fact I can if I wanted take down the SP10 in its current config and set it up in a full plinth in one day. I have been searching for pictures of the different stages of plinth build I did. But they were taken with my old Blackberry (fwiw - A POS Canadian company that I lost money on -sorry for the rant). If they show up on a hard drive somewhere will post them. this thread brings back a lot of ANALogue memories.
Personally am intrigued over your moniker. I think it is really cool. Does it have meaning behind it ?
Timeltel. Ha.. I marvel at the little things in analog that make big differences. Then we are trying to accurately measure an exceedingly little thing. I also marvel at the existence of intelligible music via a record given the "complications" that exist.
I would say that without stylus drag you have no music. The force it imposes is significant, observable and varying. It is one factor that must be considered when putting together a TT.
you say: I used to say to myself ...hmmmm looks like a hole / space there. Wonder what would happen if I filled it ? When an audiophile based on theory alone, said don't do that, its not right because of xxxxxxx, but showed no real direct experience with it himself...... ..Hell..the more reason to go and do it.
This is a tad unfair given that you don't know what I do do, and what else I have built and fiddled with.
But FYI i have made a few Lenco plinths, and have also fiddled (that's what I call it) with a few belt drive decks to. In addition to this I have built quite a few speakers. In my experience when you keep mass loading you effectively just restribute the vibrations to a higher frequency often. The strangest/worst thing one can do is fill up a plinth with some type of permanent resin, and then be unable to remove it, or indeed sell the component due to the over-enthusiastic 'intervention/innovation'
As to the Obsidian - I never knew it was glass - I had always thought it was a non-resonating composite like the one on the SONY TTS - learn a new thing every day.
Regards, Richardkrebs: Would stylus drag then be considered an irrestable force?
Just imagining the tensions these forces are exerting on tonearm bearings, the headshell couplings and the bearing wear. not to mention misalignment consequent to the rending of cantilevers as the stylus drags a seven pound pod around leaves me marveling at the complications overcome in the analog realm.
Or perhaps this might be a reductio ad absurdum (referring to my comments, of course)?
---Just an enthusiasts' mutterings amidst the opinions of experts.
I mentioned the mythical perfect TT earlier on this thread. item 2) was " Perfect dynamic dimensional stability"
We have seen on another thread here how stylus drag can slow the platter. This even where massive platters and drive systems are employed. This drag is pulling on the arm and hence its support. In the case of a nude TT, the pod is being exposed to this force. If this heavily modulated force is sufficient to slow a weighty platter of considerable inertia, would it not also be able to "tilt" a free standing pod even, if it is substantial?
Way back in high school we were tasked with this question.. What happens when you throw a snooker ball such that it hits the front of an oncoming train. The answer is that the train slows, and with relative weights and speeds, we were able to calculated how much.
I tapped the armpod and shelf (plinth) with a metal object whilst the stylus was on a stationary record...and the tone of both was near identical.
I was referring to the sound you get not through the speakers but just the sound of the metal itself reacting to being rung by tapping it with a metal instrument.
should have waited till I was fully awake and finished my coffee before I hit submit. sorry for the errors - extra words that don't belong.
A case of mind and fingers not in sync yet. LOL - to edit the post in this forum database, would seriously throw out my carefully thought out paragraph alignments. :^) l am going for my run instead.
Dgarretson have you considered filling the webbed aluminum casting of an SP-10 with a dense hard mixture of industrial epoxy and crushed granite(similar to Verdier) or brass powder?
Parrotbee With regards to filling in the SP10 - Can I just suggest that you are a bit careful - why not try some lightweight damping such as acoustic foam first of all - what frequencies are you trying to damp?
Many times you don't know what frequencies, until you hear something better (in your own room) and it could be anywhere in the frequency range. Had the TNT at the time. Brought in the SP10. The SP10 did one thing better. I changed the TNT to match it in that area. Brought in the JN Lenco. It did something better than the TNT and the SP10 in my room, so I adjusted both of them to be better. The adjustments were many to the TNT and SP10 back and forth and the cycle continued. The JN Lenco is the only TT I never touched, and if you own one you know why. The thing has no reason to sound good when you look at how a base stock Lenco TT is put together. The only thing good about it is the motor. But JN as one example, has built many versions and learned along the way. One thing that is not obvious with it, are the purpose voids built into the the plinth around the motor/top plate and the armboards. You need to look at it from upside down to understand what I mean. His table is Function over Form and the result of many adjustments to plinth and motor. I thought about building one after the SP10 then this one just kind of fell into my lap. Anyone thinking they can just make a giant plinth and drop a Lenco into it and call it a day ...well I better stop what I was going to say. Because they can do just this it. Once you have done this do a close compare to a Nantais Lenco.
The DD SP10 and I assume the Denons, Victors, etc... are different. They are self contained units. Like I said if I was curious and had time and money I would start taking it apart. Mine came from a private studio and was never in a radio station. I actually had two one at one time; one was down in the city when I was spending alot of time there.
When you are Laborataire Verdier there are many tools, people, etc... at your disposal to investigate and analyze. Go through all the proper project management phases. When you are moi...it is different.
I used to say to myself ...hmmmm looks like a hole / space there. Wonder what would happen if I filled it ? When an audiophile based on theory alone, said don't do that, its not right because of xxxxxxx, but showed no real direct experience with it himself...... ..Hell..the more reason to go and do it.
You said a few interesting things about the Platine, because the base is very much made of a similar material, by the sound of it, as the Technics Obsidian Bases or the Sony Reisinamic Plinths - both of which use 'resins and stones'.
I had the Obsidian base - I sold it to a "collector". Its a glass plinth - apples to oranges comparison with the La Platine's Granito base which is non-resonant.
One time I filled the four pillars of the TNT with Blue Tac.
The music became like it was coming from down under and I don't mean Aus and Nz. I mean the place where the horned one lives. where it is always very hot, The good thing from this experiment was I have so much Blue Tac now that I re-package it and give it out as Christmas gifts to audiophiles. 1,325 uses so far for it. Did you know you can clean your stylus on it?
02-09-15: Pryso Halcro, do you have any idea how that tower plinth builder now has access to bolt/unbolt the motor unit or change wire with the tonearm if necessary?
Form does not seem to follow function?!?
Pryso
If indeed there is a beer fridge in there. then it is Function over Form
Pryso, I imagine that the Victor TT is simply 'sitting' on the plywood plinth (as it sits on my stainless steel cradle)....but I can't envisage that the power cord exits at the base of the 'coffin'...❓ There are probably holes in the rear of the plinth for the exit of the power cable and also any tonearm wiring.....although with most modern arms the cabling is above the plinth. Otherwise Chris may be correct.....there is a large door at the rear for the storage of beer....😜
Atmasphere, It appears to me (from the photo of the lathe) that the platter support is inside the supporting base which must also enclose the drive system. The cutter appears to be mounted on a 'rail track' fixed to the surface of the base which allows positioning and clamping of the cutter machine.
I'm not sure I follow your directly fixed arm description for my set-up...? Could you perhaps elaborate....👀❓ I tapped the armpod and shelf (plinth) with a metal object whilst the stylus was on a stationary record...and the tone of both was near identical. Whilst no sound was heard through my speakers when the shelf was tapped...a very slight 'tap' could be heard from the midrange driver when the armpod was tapped.
Halcro, I can't make out from the photo how that cutting lathe is set up. Our lathe incorporates the platter bearings and the bearing track for the cutter head itself as a single piece of metal (which is quite massive).
With regards to the photo of your 'table, if it were me I would have not employed a tower and armboard to mount the arm, instead I would have affixed the arm directly to the plinth, which, in order to accommodate the platter as shown, would have been rather massive. The reason for this is that the tower and armboard both represent moment arms which can vibrate interdependently of the plinth itself. A simple test for this would be to tap the armboard with a metal instrument and then compare to the tone thus created when tapping the plinth. If different, a coloration is imparted.
Its an illusion Henry, just like the hanging balls on my SP10. In the back is a door, it opens up to a beer fridge. A beer fridge for now. It will double as his coffin when the time comes. This is the only reason his wife allowed it in the house. :^) I am surprised by your picture of the Victor that you only teased us with a glimpse of what is next to it. The now famous Canadian. In an obvious skeletal multi layer plinth.
I do appreciate the added 'warm and fuzzy' feeling this can impart together with the ability to mechanically fix the tonearm pods if their weight is insufficient....but apart from that..
right now in the middle of this cold winter - warm and fuzzy is sounding real good to me.
Parottbee - I found it a bit too warm for my tastes.
If we look at the bottom left side of the graph warmth is shown in the 150 - 250 hz range. We all have our own personal tastes, different types of music we like to listen to. If I am with a friend setting up a system and they say something sounds too warm. I am assume it means an over emphasis in this 150-250 frequency range. You can have too little bass and it will over emphasizes the highs, or too much bass and things start getting muddy real quick. Get the bass right and everything will fall into place. With vinyl (due to different resonances, vibrations) you can mess things up really easy; but you can also fix things up as well. The warmth can be fixed a number of ways. Two ways that might work. Raising the VTA a bit (or) assuming the speaker/amplifier relationship is a compatible one, adjusting the speaker location to the room boundary; or maybe just their angle depending on type of speaker to balance out the sound. If a guy (no woman audiophile would do this?) has 500 lb speakers. What are the chances of him moving the speakers around for adjustment to the best music from different turntables. Some tables produce music that is weightier, heavier, a fleshier sound. There is more meat on the bones. My direct experience in my room, La Platine is one of these tables. It can easily over power the room with too much bass and be out of control. There is a learning curve with it.
Also imo just for thought. These public chat forums are no different than a bunch of guys getting together for a night of poker. There are different games to play. Some games have cards showing others don't. Some on Audiogon here are showing all their cards (virtual system) others none. Showing a list in a virtual system is one thing. Showing a room picture showing speakers and walls is the real deal. Showing this info allows for a better sharing of info and learning -
Dave G - WOW Big News. This audio business is crazy. As far as a I know no one is getting rich on it, and it is IMO all about audio passion. You have my utmost respect for entering it like everyone else. I have been asked to become a dealer 4 times. I turned them all down for personal reasons.
Wonder how many professionals (manufacturers, dealers, distributors, special interest individuals) are on this thread so far ?
The JVC TT-101 drive unit is now installed in 40" tall, 280 lbs (!), solid birch plywood, and using the Zeta tonearm and EMT HSD-6 cartridge, This is now the best TT I have ever heard, bar none (including the Kuzma Stabi XL4 with the airliner air bearing arm and Dynavector XV-1 cartridge). The sound-floor is 'Dead Sea' low, background is pitch black, the tonality is accurate (meaty and full bodied) and the dynamics are explosive. The top end is creamy smooth (speed stability). I am very happy I went ahead with this project...
...a stock Lenco starts with numbers like 60 dB S/N, wow and flutter at 0.6% and with a 4 pole (!) motor when the JVC TT-101 is a core-less motor with 75 dB S/N (DIN B), 0.02% wow and flutter. One can argue about torque differences and cartridge drag on transients, but then how much torque do you really need?!? One owner tested the TT-101's speed stability with a laser when 3 tonearms and cartridges were mounted and playing at the same time and got zero deviation. Compared to my previous Oracle Delphi Mk II, all the micro dynamics that the Oracle excels at, are there but with even extra air and detail. However the Oracle sounds like a CD Player compared to this TT. Watered down, anemic and lacking harmonic completeness, meat/substance and macro dynamics.
What Halcro says then explains why people like Mike Lavigne are using very expensive microscope stands in their systems.
If you talk to those who have changed to a wall-mounted shelf or active isolation stand or concrete slab-on-the-ground installation....they will likely express amazement at the reduction in noise-floor and the silent 'blackness' they now hear through the turntable system. My vinyl playback system is quieter than CD...😎 An easy test for any turntable whether mass-loaded, suspended, plinthed or plinthless....is to place the stylus on an unrotating record and gradually turn up the volume of the preamp. If a droning feedback sound commences and increases without further volume turning.....you are hearing Structure-Borne Feedback through your floor and/or rack supporting medium. If you are able to turn your volume to maximum with total silence (even when lightly tapping the plinth)....you are probably free of feedback issues. 😘 Good luck....
Halcro, having bushwacked a VPI TNT through flywheel, thread drive with custom pulley assemblies to minimize belt creep, and a Mark Kelly AC-1 two-phase controller, I conclude from experience that that way lies madness relative to DD. IMO there are greater evils admitted through quadraphonic rubber belts than by heroically built cantilevered tonearm boards.
Dgarretson, The big Micro SX-5000/8000 turntables are well respected but I've never been a fan of their arm-board cantilevered mounting systems. Here is an example of a DIY project using the Micro system. The structural integrity of the armboards fixed onto stainless steel poles via friction becomes less and less convincing the longer the cantilever becomes to support 12" arms. The flexural micro movements in the armboards increase according to the square of the distance of the cantilever whereas there are no deviations in a mass-loaded fully supported armpod. The fact that these (and others like them e.g. Raven) work....is perhaps an indication that actual micro-movements are still too tiny to be destructive..? However....like my mate Lew....I just don't like the 'theory'...😎👀
Thought I might just share this image of a cutter on a 'shelf'....? I think the emphasis on the mass and fixity of the cutter arm compared to the platter shares the thoughts on my Copernican view of the turntable system?
Glad to see you're off the DIY and enjoying the music...as Raul used to say? Here is a 'suspended' nude Victor TT-81 design using the same idea as your coupling 'plinth'. It all depends on what one 'means' by a plinth? If an added shelf sitting on a shelf qualifies as a plinth....well, that's exactly how a turntable plinth acts. If one removes the 'added' shelf (plinth)....could someone please explain the differences to the mechanical and structural functionalities? I do appreciate the added 'warm and fuzzy' feeling this can impart together with the ability to mechanically fix the tonearm pods if their weight is insufficient....but apart from that...👀❓
Hi CT0517 Hijack the thread all you like - ;) You said a few interesting things about the Platine, because the base is very much made of a similar material, by the sound of it, as the Technics Obsidian Bases or the Sony Reisinamic Plinths - both of which use 'resins and stones'. Likewise Townshend Audio used to use Plaster of Paris. I have to say I auditioned a Platine, and at the time I was not seduced by its charms - I found it a bit too warm for my tastes. That said - I am not knocking what floats your boat. With regards to filling in the SP10 - Can I just suggest that you are a bit careful - why not try some lightweight damping such as acoustic foam first of all - what frequencies are you trying to damp?
Hi Pryso and Richard, Devcon appears to have soft properties similar to Dynamat or rubber. I lean rather toward passing vibration to earth through mass loading, hard coupling, together with structural improvements that increase mechanical stability of the cast housing and motor. As Richard suggests, maybe at SOTA the stock casting should be discarded. Nevertheless . the cast housing and motor could be good candidates for treatment via the Flex-tec epoxy system. This epoxy and hardener form a semi-solid that can be sculpted into firm shapes. The casting and motor cavities could be filled and thickened without molds, drips, or overflow. The motor mount bosses could be enlarged to increase rigidity. The epoxy could be filled with brass powder or lead sheets to make a semi-metal or CLD compound, and shaped irregularly to break up and spread out resonant signatures. There Ive almost convinced myself to do it.
CT0517, Your skeletal plinth is close to what I have in mind, absent several wrinkles to come. Among other things mine will support 3-4 arms, be compatible with Micro Seiki/Gunmetal pivoting arm bases, and have direct metal-to-metal coupling between the motor spindle bearing and the arm pillars. Im working with a platform manufacturer with the expectation of making it commercially available for SP-10, Denon, and JVC DD. The business case and cost structure for an initial CNC production run would be improved by anyone expressing interest in this. If so, feel free to PM. Is there room in the market for yet one more supplier of plinths for vintage TTs?
Dgarretson Ct0517 and RichardKrebs, have you considered filling the webbed aluminum casting of an SP-10 with a dense hard mixture of industrial epoxy and crushed granite(similar to Verdier) or brass powder? This might give the casting the properties of a massive plinth, while performing in conjunction with a rigid skeletal "plinthless" sub-frame.
@Dgarretson
Hi Dave - did not realize you picked up a SP10MKII. another TT ? Filling the webbed aluminum casting sounds like a good idea. But when you say "plinthless" with my set up it is not the case. if i can backtrack.
I got to about Version 8 with my SP10 project (two + years ago?)
The plinth can be seen as the black base that the stainless steel columns and pod are bolted into.
It has not been touched in a long time. I admit its looking kind of stale and I always meant to replace the current black base with a more aesthetic one. This hobby is very much an exercise of Function over Form for me. The tonearm attached to the POD is a leading example of this. If for some reason one "hears" a mismatch in resonances, the ET2 provides resonances tuning capability. If I had continued with the SP10 I had thought of maybe dropping its black pants and have a look at how things can be cleaned up. I discussed with Richard Krebs, sending it to him long ago.
however.... as I am really enjoying not reporting to a boss (wife not included) I need to be selective with funds for the hobby as I have two 20 years olds grabbing cash at every opportunity. Its not a priority and the sp10 is in room 2. All my vinyl listening is on La Platine in room one.
fwiw (sorry to digress Parottbee) My turntable phase was a very slippery slope for me. It came at a time when I needed something to take my mind off other things. I am very grateful for it and I learned much with my SP10MKII. I am happily a music lover these days, with no desire to tinker, although I don't mind talking shop on the forums and discussing past experiences. I did have at the height of my own personal madness - three tables, modded VPI TNT ( thread drive), SP10MKII and Nantais lenco table (which btw used to be his personal table), all next to one another like babies in a nursery. I had the same tonearm / cartridge going with two of them at a time, and it was alot of fun comparing to 15 IPS master tape dubs - very revealing.
Back to the thread theme if I can just say that discussing the type of plinth is only one aspect of this. The platter system is very important. For example the Jean Nantais here is what the platter looks like
I have a copper mat I can use with the technics.
The Verdier however again sets the mark - a solid aluminum platter designed to be used Naked. With the magnetic levitation the natural action of magnets producing a braking action. So you have acceleration inertia and and braking due to the opposed pole magnets to deal with the records behavior. Add to this a solid aluminum rigidly attached pod, a different material brass spindle to interact separately from the platter. oh yeah also no bearing....... Just bloody brilliant. Continually amazed by the simplicity of it. In all my years at this hobby probably the best thing I have acquired right there with my SP11 (and my records)
Henry - Lewm seems to showing (again) what we in Canada refer to as - possible signs of cabin fever. I could be wrong . But if I am not mistaken there have been some bad snow storms in the US lately. :^)
God, these analog threads make the digital ones seem SO BORING....... no more coffee for me. :^(
Halcro and Lewm - it's like those two old men on the muppets - always arguing - probably really the best of friends/enemies??? Funny thing is that both write about some of the best posts on this forum from my reading. What Halcro says then explains why people like Mike Lavigne are using very expensive microscope stands in their systems. That said don't RIAA filters etc cut out above 2-5 hz? I guess I am gonna have to put theories into a design, and then tune using my ears.
Once again, you've written nothing that comes remotely close to changing my mind about outboard arm pods.
Dear Lew.....my mate...😍 It is not my desire to change your mind about anything... I know better..😏 I simply use my ears and listen to actual examples BEFORE I blindly theorise.. Chances are I'll be back in the States before you make it to Oz..❓ If there's no Fosters there...a nice Chivas might have to do...👍
Hi Henry, I was hoping you would come out of your recent shell. Once again, you've written nothing that comes remotely close to changing my mind about outboard arm pods. However, I do agree with you on some of the other issues... Where was it exactly that I was talking about "airborne feedback". That's your pet bugaboo; you raise the issue in order to beat it to death. I've never used the term.
The way I read Atma-sphere's post, I should think you would have to disagree with some of it. He is saying what I have always said. To wit, "To this end, the coupling between the bearing and the base of the arm must be as precise and tight as possible; IOW of a singe piece which will not respond to vibration, as if any differences can occur they will be interpreted by the pickup as coloration."
Take a look at an L07D some time. There is the epitome of what I and Atma are talking about in terms of "coupling".
All of this folderol aside, I have come to think of you as a friend and I would love to argue these silly issues with you over a Foster's, if and when I ever make it back to Oz.
This is/was essentially my longstanding argument with Halcro vis a vis outboard arm pods.
Lewm seems a nice sort of guy but I can't bring myself to continually explain why his analogies are often theoretically inappropriate. In fact Lewm, over the years has demonstrated a clear preference for 'theoretical' analyses over actual 'listening' experiments. Virtually all the turntables I have listened to over the last 40 years have had a plinth and firmly connected armboard... In fact I have just such a table mounted on exactly the same wall-mounted shelf as my skeletal table so I can actually LISTEN to both versions sitting on exactly the same "row boat"....
Here is the issue in mechanical engineering terms. It is not a lot different from the steering and suspension of a car.
In a nut shell:
the plane of the platter must be consistent with the plane of the cartridge. As the arm moves the cartridge must remain in this plane. Since the platter must revolve, there can be no slop in the bearing such that the platter can deviate from said plane.
As the arm must be set at a fixed point, it can then be seen that if there is any difference that occurs between the point of the arm and the surface of the platter that is will manifest as a coloration of some sort.
For this reason, the coupling between the surface of the platter and the locus of the cartridge cannot have any slop of any sort. To this end, the coupling between the bearing and the base of the arm must be as precise and tight as possible; IOW of a singe piece which will not respond to vibration, as if any differences can occur they will be interpreted by the pickup as coloration.
What this means is the more dead and the more rigid the plinth is, which also holds both the arm and the platter, the better the 'table will sound.
Now there is essentially nothing in Atmasphere's Post that I disagree with.. In my case, the rigid plinth is the wall-mounted shelf which is disconnected from any wall and floor Structure-Borne feedback...and that is really the most common problem with most turntables' support systems. They are usually connected to racks sitting on suspended wood or concrete floors which are structurally deflecting under their own weight as well as live loads. These structural deflections induce low-frequency soundwaves into the suspended floor systems which are often below 5Hz and this low-frequency 'movement' cannot be stopped by racks or plinths. That's why specialised stands designed to cancel out 2-5Hz Structure-Borne movement are used to support electron microscopes. Air-Borne feedback is virtually a non-issue in all but a few extreme examples. Once your rack and plinth are experiencing 2-5Hz structure-borne movement....you are on the Titanic and thinking about the safety of individual row boats..for one thing is certain.... The ship is going down...👀
Your idea for damping the SP-10 frame is similar to what a friend (physicist) suggested to me some time ago to damp unwanted vibrations. He suggested using Devcon Flexane 60 to the underside of a surface to be damped. The listed properties include "absorb noise and machine vibrations". http://www.itw-devcon.co.uk/index.php?/devcon_mro/flexible_urethane_maintenance_and_repair_systems/devcon_flexane_60_80_94/
It would seem a simple matter to apply. It would not have the mass of your ingredients but if I understand the product, as an elastic material (does not fully harden) it would server more as an absorber for vibrational energy.
Dgarrestson. I have removed the motor housing on my MK3 from the original square chassis See the triangular shaped TT on my krebsupgrade.com web site.
The rather flimsy naked motor housing has been laminated ( epoxy glued and bolted) into a machined duralumin housing of 15mm wall thickness. This in turn is adhered to a 15mm thick lead disc. ( the piece that was cut out of the plinth to accommodate the motor)
In my original post on this thread, I talked about minimizing material changes and joins in the platter arm loop along with consideration of propagation speeds, absolute dimensional stability and stillness. This leads to the conclusion that the chassis has to go.
I also replaced the platter with an acrylic duralumin lead composite.
Ct0517 and RichardKrebs, have you considered filling the webbed aluminum casting of an SP-10 with a dense hard mixture of industrial epoxy and crushed granite(similar to Verdier) or brass powder? This might give the casting the properties of a massive plinth, while performing in conjunction with a rigid skeletal "plinthless" sub-frame. I've been think of this for my SP-10 MkII, together with a turnbuckle between a threaded bearing well and the sub-frame similar but different to the Porter concept.
Viridian et al, You guys may be missing the point of what Atma-sphere wrote (at least as I see it). The point is that whatever the resonant signature, it is critical that the tonearm and platter be "connected" so they resonate as one piece. The problem with outboard arm pods (again, as I see it) is that they separate the tonearm from the bearing/platter, and no matter what you do after that, the two entities are independently subject to environmental energy sources; they'll then move or vibrate differently in response. Best you can do is make them very very massive so that most energy is dissipated as heat rather than movement. This is/was essentially my longstanding argument with Halcro vis a vis outboard arm pods. My metaphor or thought experiment is: Think of yourself trying to cut a diamond while seated in a row boat floating on water. Now think of yourself trying to cut a diamond whilst you are sitting in one rowboat and the diamond and all your tools are in another separate rowboat. Which is easier to do accurately?
Some 20 years ago when I was building my current SP10 MK3 plinth, I spent a lot of time experimenting with glues. I was using CLD on the acrylic top plate. In this case a 15mm layer of lead was to be adhered to the acrylic. I initially thought that a lossy type glue, such as ados, would be optimal but listening to the test pieces thru a stethoscope while tapping it gave a "thunk" type sound. This was not what I expected as I was trying to emulate the ideal water fall type plot as we see published in speaker tests. That is a sharp rise time with very little tail to the sound. I then started experimenting with epoxy glues and settled on an industrial araldite epoxy. This lead to protracted experimentation with harder and filler ratios. I found that I could further reduce the tail of the tapped sound by optimising the hardness of the glue. The final result gave a very short sharp "tic" when the workpiece was struck. The result was a kind of fusing the acrylic to the lead. In this way they behave as a intimate composite structure. Aiding this was massive clamping pressure while the glue dried. Over one tonne of cast iron billets were stacked on top of the plinth during the curing time. Epoxy heats up when mixed, so the glue becomes quite runny. The vast majority of it oozed out between the layers. Unwilling to let this excess set, which would have required expensive remachining, I spent almost all night until just before dawn removing the excess as it flowed out.
Made a table a few years back from Cocobolo laminated with Aluminum, glued the 5 layers (3 cocobolo 2 aluminum) together with a 2 component Epoxy glue, still hold up very nicely. The aluminum layers were "timesaved" which is the typical graining you see on for an example your typical Face Plate. System 3 Epoxy
I know this may seem pedantic, but is there a special glue when gluing together layers - in other words - what glue do the likes of Kronos and Clearaudio use when sandwiching aluminium and panzerholz
A further point following Viridian and Ct. When I first became interested in DD tables Corian was often mentioned as a recommended plinth material. But then I read more than one negative comment on that. Further reading disclosed that Corian includes some amount of aluminum flake in its composition. Apparently that varies among samples and that quantity can have a sonic impact. Bottom line, simply choosing Corian may not allow prediction for how it will sound.
Unfortunately it seems to me the best answer is to follow Ct's path and experiment with alternatives.
Viridian Given that any structure has a resonant signature, the question then becomes not, "which is the most dead" but "at what frequencies are the resonances in the structure and what is the amplitude, magnatude, and Q of those resonances?"
+1 Excellent Viridian
One example of this.
"Granito is a material composed by little pieces of marble of very different origin agglomerated inside a mold with cement. Machined and polished. The resonance of the plinth with its suspension is about 5Hz and it is well absorbed by the air cavities"
Mr. J.C. Verdier (R.I.P) in describing the Verdier Vintage La Platine Granito.
Along with La Vintage Platine, I also "still" own two full plinth TT's, My 100 lb Jean Nantais Lenco, and an SP10MKII that can actually be put in one of two configurations. 1) A Full Plinth - 70 lb Multi 6 Layer Birch/ One layer MDF or 2) a Rigid (in your words ParrotBee) Skeletal Plinth.(both plinths which are DIY sourced and put together). The SP10mkII is sort of a pet project going way back now. fwiw I prefer it in its Rigid Skeletal Plinth form. It is more neutral sounding.
I must say that I am not a big fan of arm pod mounts for turntables because then you are reliant on the platform to couple the platter cartridge arm loop - I am sure some will outcry at what I have said, but I think arm pods are quite a clumsy solution to a problem. I had a look at few different large microscopes, and they have motion control dampers - I am looking into the best VFM/performance ratio. I am gonna post, at some stage, a full set of pics from my drawing board plans to the build.
Parrotbee I look forward to you posting pics of your creation. Good luck with the project. Also can you advise more details on the microscope isolators?
Atmasphere Dimensional stability.... You said it far better than I
Here is the issue in mechanical engineering terms. It is not a lot different from the steering and suspension of a car.
In a nut shell:
the plane of the platter must be consistent with the plane of the cartridge. As the arm moves the cartridge must remain in this plane. Since the platter must revolve, there can be no slop in the bearing such that the platter can deviate from said plane.
As the arm must be set at a fixed point, it can then be seen that if there is any difference that occurs between the point of the arm and the surface of the platter that is will manifest as a coloration of some sort.
For this reason, the coupling between the surface of the platter and the locus of the cartridge cannot have any slop of any sort. To this end, the coupling between the bearing and the base of the arm must be as precise and tight as possible; IOW of a singe piece which will not respond to vibration, as if any differences can occur they will be interpreted by the pickup as coloration.
What this means is the more dead and the more rigid the plinth is, which also holds both the arm and the platter, the better the 'table will sound.
Hi Richard I said the SME's are skeletal on the basis that they are quite open as you observed. I must say I do quite like SME's. My problem with the double deck turntables is that dust can gather - however clean your room -trust me I have one such deck. I have in mind the use of adjustable oil filled motion control dampers (used for microscopes) and heavy elastomer springs. It will hopefully allow me tune the deck but not be too springy or overdamped. Who knows maybe I can rope some local gonners into doing some listening tests at my home...
Parrotbee. I think that good inspiration can be found if we look at how cutting lathes are constructed or outside of the industry, we can look at how milling machines are put together. These devices are required to hold a fixture precisely in place relative to the work piece, (record blank or machined material), whilst being dynamically loaded. This is exactly what a TT is asked to do.
No issue at all with a suspension if the siting of the TT dictates. My installation is basically fixed to the concrete floor and mother earth and I believe that this approach yields good results. Of course in most situations this technique cannot be used, so a suspension is a good solution.
Interesting re the SME's, ok you can see their entrails but their is a single structure carrying the platter bearing and the arm. In this respect they are pretty conventional. However the box that encloses it all is missing. This is likely a good thing.
Damping is a real can of worms. It's use can yield fantastic results or it can suck the life out of the sound faster than a death eater in a Harry Potter Movie.
propagation speeds.
Yes in this case transmission velocity of sound thru the material.
for example: acrylic is around 2700m/s copper is around 4600m/s
Hello Richard - thanks for your contribution as I know that you've probably forgot more than most people know about decks. Most of the 1970's DD's of yore seemed to all consistently have heavy plinths. The decks having been designed at the height of vinyl when the multinational companies really threw all their resources at turntables - so they probably knew a thing or 2 I guess. Not being funny when I say this, but I also consider the SME range of decks a skeletal design - albeit with high mass. I personally quite like the idea of combining reasonable mass, intelligent damping, and suspension. I have read around, and some people take just one concept, be it mass, suspension, a single tasty material - and then they use it to the absolute extreme thinking it is the be all and end all. By way of developing my point if mass alone were the way forward then one would fix a turntable into the stonework of their homes. I am going to have to read a bit more on propogation - in laymans terms does that relate to how a material in fact transmits, or absorbs a given vibration or sound?
IMO a perfect TT needs to satisfy three criteria. 1) Perfect DYNAMIC speed stability. No drive system meets this and passing the (in)famous timeline test is zero guarantee of dynamic speed accuracy, only average speed accuracy. 2) Perfect dynamic dimensional stability. Impossible unfortunately. My view is that a skeletal design makes this goal more difficult to achieve since we are introducing the support structure, shelf, platform, into the equation. It effectively becomes the plinth. Related to this is the minimisation of joints and material changes in the platter-arm loop. 3) Perfect stillness. Again impossible, but careful choice of materials and correct implementation of single point mechanical grounding or isolation, would likely be advantageous. This too suggests that a skeletal design is not optimal.
A heavy, inert, one piece plinth is indicated if you agree with goals 2) and 3). I will not open Pandora's box with any comments about goal 1).
Propagation speeds of the materials chosen also need consideration.
Find the thread started by Halcro on the "Copernican Theory". The theory does not expressly deal with your question, but Halcro is a devotee of the open, non-plinth plinth. Good arguments pro and con to be found there.
What you say about low rpm equating to low vibration is probably true enough, but belt-drivers would say that the belt affords isolation from the motor. Most direct-drivers (like me) prefer very very heavy plinths, but then there is argument about what is the best material: wood, exotic wood, slate, granite, etc.
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