So what about the plinth?

[jgordon]

As I look at the situation again today, I realize it would be even easier than I thought. Simply switch the top plate and the bottom plate of the motor, and your mounts are pointing down instead of up.

Then it's just a matter of measuring and constructing a plinth to support the newly oriented mounts, while maintaining the correct height for the pulley. In which there's actually a good deal of play, as you ca slide the pulley up and down on the motor shaft.

 

[jgordon]

Please do. I can think of at least two people who would be very interested in reading about it.

people do detach motors from idler drive tables. I remember reading a couple of articles about it. I will dig around and see if I can find something for you , I am pretty sure it was being done with garrard 301/401's but I could be wrong on that.

 

[tromba]

Off the top of my head thinking about the armboard mount:

so the top without the armboard looks like this:

Instead of having the armboard, suppose those holes the armboard covers up were part of the plinth rising through those spaces?

Of course this makes changing armboards nearly impossible.......

 

[tromba]

This may answer my previous post....

I quoted from J.D. at vinylengine.com earlier in this thread. Here's a comment of his I found on using armboards:

Your second question, about separated arm mounts, is unlikely to get resolved here, but here's one vote for integrated, or non-separated arm boards. In the near-century of phonography before the 1980s, this was an undisputed rule.

The planet rolls, the oceans rock, the plates scrape, the seismic activity doesn't stop. Nothing on earth is 1oo% stable. With a device like a record player that hopes to extract microscopic information from modulated grooves, it's imperative that the reader (stylus-cartridge assembly) and the information (rotating groove) be locked into the same plane, the same exact operational coordinates. So that no additional instability is added by separating them.

Separating the tonearm onto an unconnected tonearm 'tower' creates differing vibrational circumstances, at micro-levels, for the alignment coordinates of the two systems (revolving info and pivotted reader).

Picture two cars in slow but steady rush-hour traffic. Picture leaning out of your car to write a quick postcard, leaning the postcard not on your car but on the fender of the adjacent car, as both of the cars travel along. Difficult to achieve accurate transcription with shifting alignment parameters, even slight. That's an exaggeration of the effect, but it's not different in kind.

At very least the separated armpod tower adds more complexity to the task of the tonearm's bearings which must now negotiate a still-very-complex job, but now with its moorings wholly separated from its objective. Turntable design generally makes improvements through advantageous simplification, not adding complexity.

A separated tonearm 'tower' seems to have had a trendy moment, some time after the separated motor-pod fashion came about, which was a bid to lessen noise and rumble. Both separated towers or pods kind of look cool, in a tech kind of way. But both approaches in my view add more problems than they solve.

I see the logic in that. The problem then is, I suppose, to keep the armboard mounted securely to the top of the table, but somehow isolated from vibration

EDIT: Followup post from J.D. on vinylengine.com

Perhaps the difficulty here is in visualizing what's considered 'separated'.

I'm not at all stating that complex armboard mounts are wrong. Far from it. With cartridges, stylus profiles, headshells and tonearms being such a disparate group these days, I'm all for experimenting with layered and complex armboard mounts, for both noise isolation and tonal presentation as well. And there are strategies for barriers / labyrinths while still locked mechanically, same structure, to the turntable transport, that aid basic noise isolation.

It's the physically separated arm-tower, disconnected mechanically from from the platter transport, that is wrong and adds unwanted complexity to the already sizable taskload of the cantilever and the tracking arm.

Is waterjetguy still around? Am I running off in a tangent?

 

[totem]

Reading your post/quote on separating the arm, does not convince me that it is a bad thing.
A single opinion is just that, until I see some additional info or better yet data.
Keep the questions coming.

 

[tromba]

Reading your post/quote on separating the arm, does not convince me that it is a bad thing.
A single opinion is just that, until I see some additional info or better yet data.

I agree. But the logic seems there, although I don't know about the science....

 

[tromba]

Isolating motor

HERE is a page where someone wrote about using different motor mount bushings. Can't find who wrote that page

I found these that look similar, and might be from here

 

[jgordon]

I'm not sure I buy into the theory that you want your platter and tonestm mount vibrating at the same frequency. I'd think you want none of them vibrating. If you can cost-effectively rigidly mount your tonearm, I'd say go for it. Then start isolating and damping your platter and motor. At a minimum, I would (and will) investigate some sorbothane or rubber washers to place between the arm board and the top plate when I mount everything back up.

But far more designs incorporate an isolated motor, and a shared platform for the tonearm and platter. So if your carpenter friend is up for the challenge, I'd begin with the flipped motor mounts attached to the plinth, and the top plate isolated with sorbet hand or rubber mushrooms. I might also dispense with the metal rings on the mushrooms, and just use a thin coat of grease to allow the adjustment wheels to turn smoothly.

 

[jgordon]

I can't imagine these are anywhere near $55 from the source. If you inquire and are thinking about a group buy, count me in. That said, my gummimuffins are surprisingly gummi considering their age.

HERE is a page where someone wrote about using different motor mount bushings. Can't find who wrote that page

I found these that look similar, and might be from here

 

[J.D.]

I'm not sure I buy into the theory that you want your platter and tonestm mount vibrating at the same frequency. I'd think you want none of them vibrating. If you can cost-effectively rigidly mount your tonearm, I'd say go for it. Then start isolating and damping your platter and motor. At a minimum, I would (and will) investigate some sorbothane or rubber washers to place between the arm board and the top plate when I mount everything back up.

But far more designs incorporate an isolated motor, and a shared platform for the tonearm and platter....

It's not that you 'want' any vibrations at all. It's the proposition that once you have a situation --vibration in the motor>platter direction-- you can't expect to remedy that by putting your armboard outside of the issue. You can't have one system humming on motor pulse and another dead-still on the shelf and expect the cart/tonearm to resolve it. (There was this one approach with a laser beam that could, but that was a different story..)

I think there are more contradictions in having an outboard armboard system, in its own geometric/resonant zone, attempting to resolve & transcribe a rotating groovewall in a wholly different geometric/resonant zone. I say geometric here, because one system vibrating on compliant supports is simply not going to be in sync with another system vibrating differently, whether less or more, slower or faster, perhaps on another set of different compliant supports.

But I'm just an analog enthusiast; don't take my word for it. Have a look at a Verdier. If ever there was an attempt to isolate vibration, this is it, with motor on the other side of the room and the platter mag-levitated. But look at their armboard. Locked onto the plane of the platter position.

Look at Linn, Avid, Vpi, Brinkmann, Emt, Thorens, Rega, Yorke, Kuzma--- virtually all of the manufacturers, whether they separate the motor or not, never interupt the planar relationship between platter and armboard.

And that's because any deviation here will interupt alignment, no matter how minutely, and even if temporarily, will cause tracking error, will blur resolution.

As far as I am aware, the only time you will see an Outboard Armpillar construction that isn't mechanically locked into the platter's position is in the realm of over-ambitious Diy'ers.

And yes of course, as an outboard arm assemblage approaches immoveable massiveness, the differences are going to get smaller, but the Turntable as we know it for now is constructed, by prevailing wisdom, with a captive, locked-on armboard.
J.D.

 

[waterjetguy]

This may answer my previous post....

I quoted from J.D. at vinylengine.com earlier in this thread. Here's a comment of his I found on using armboards:



I see the logic in that. The problem then is, I suppose, to keep the armboard mounted securely to the top of the table, but somehow isolated from vibration

EDIT: Followup post from J.D. on vinylengine.com



Is waterjetguy still around? Am I running off in a tangent?

J.D. brings up a good point: what is really being gained by mounting the tonearm separately? I only see a benefit if the plinth is noisy, but in that case the platter is almost certainly noisy, too, unless it is isolated form the plinth.
If the tonearm is to be mounted on a separate platform, then it would be a good idea to isolate the support that the 'table and arm both sit on. Maybe a granite slab on isolation feet.

I addressed isolating the tonearm or tone board in an earlier post. Must be be solidly mounted so as to maintain positional accuracy to the platter, which rules out any method with much "give". Relatively stiff rubber mounts would be useful, like the o-rings used on SME arm mounting bolts.

I think that placing the platter and tonearm on the same, well-isolated, base makes the most sense.

In your case, moving the motor to isolate its vibration from the plinth will probably offer the most benefit. That gets the primary vibration source out of the platter/tonearm picture, as described above.

 

[tromba]

but the Turntable as we know it for now is constructed, by prevailing wisdom, with a captive, locked-on armboard.
J.D.

First welcome to AK!!! I assume you're the same J.D. that I've quoted earlier?

Thanks for your input. I've certainly learned a lot in the last week or two!!

EDIT:

don't take my word for it. Have a look at a Verdier. If ever there was an attempt to isolate vibration, this is it, with motor on the other side of the room and the platter mag-levitated. But look at their armboard. Locked onto the plane of the platter position.J.D.

I looked at them. 400 kilos? Pretty amazing. I couldn't see a price, but imagine it's several years worth of what I make!!!

 

[tromba]

In your case, moving the motor to isolate its vibration from the plinth will probably offer the most benefit. That gets the primary vibration source out of the platter/tonearm picture, as described above.

Thanks again for replying!! Was that a typo in your sentence? "Moving the motor to isolate it's vibration from the plinth..." Moving the motor would attach it to the plinth and isolate it from the platter, I'd think.

In any case, I'm hoping to get my TT back this week so I can look at this. I can't quite see it attached to the plinth and assembling the thing. I can see reversing the motor top and bottom and attaching it to the plinth, but then the platter has to be set on the plinth with the motor shaft going in the right place. Without one in front of me I can't see if this is feasible or not.

 

[waterjetguy]

Thanks again for replying!! Was that a typo in your sentence? "Moving the motor to isolate it's vibration from the plinth..." Moving the motor would attach it to the plinth and isolate it from the platter, I'd think.

In any case, I'm hoping to get my TT back this week so I can look at this. I can't quite see it attached to the plinth and assembling the thing. I can see reversing the motor top and bottom and attaching it to the plinth, but then the platter has to be set on the plinth with the motor shaft going in the right place. Without one in front of me I can't see if this is feasible or not.

Not a typo, more of a brain-o. Yeah, motor goes to the plinth, off the platter/tonearm structure.

 

[jgordon]

Tromba, whatever happened to this project? I'm starting to eye new plinths for my 124...

 

[tromba]

It's done and here's a sneak peak at the finished product

The entire thing is documented with lots of pictures and I hope to have the entire build posted very soon (this is the last week of classes, so much free time starts next week....)

 

[jgordon]

Read through the link you sent and I'm impressed. Looking forward to your write-up here, and to your discussion of the arm board.

 

[theophile]

It's a shame that waterjetguy never got around to giving us an exposition of the science of plinths.

He was banned last year.

 

[the_nines]

Yes, it is a shame.

This is one of the most informative and fun to follow threads I have ever come across on AK.

 

[theophile]

I've been here and there, trying to keep my eyes (and mind) open...

If you folks enjoy this "science of vibration as applied to turntables", I'll start working on some posts to give a more organized overview.

Off the top of my head, some of the subjects would be:

Resonance/Natural Frequency

Vibrational Modes

Damping

Vibration Transmissibilty

Scale of the mechanical information in a record groove


Keep in mind that I'm not a tunable/tonearm/cartridge designer, so I don't have direct experience with the details of their design. (Stuff like cantilever mass, typical tonearm natural frequencies, typical rumble of various bearings, etc.)

But I do have a very good handle on the physics behind all of it.

Lots of promises made here. Nothing provided in the end. There was very little in this thread which warranted Sticky status. All of his 'solutions' boiled- down to "More Mass".

I question that. There are many industries which rely upon proper isolation in order to quantify minute data like:

Electron microscopy, hologram generation, advanced immersion lithography, atomic force and scanning tunneling microscopes and many others. They don't rely on mass they utilise specialist equipment.

I fail to see how waterjetguy provided much in the way of knowledgeable answers to anything that he claimed to be a pundit of.