Building a Plinth for Lenco L75

[arj]

It's a very interesting thing that you mention Anilva. I have always wondered why Lenco did not use a heavy plinth. I am sure they must have experimented. Putting a heavy plinth is one of the easier things to do. So obviously there must have been some reason. Ditto for Garrard too. Maybe your suggestion of restoring the Lenco to its original specs has a lot of merit.

Prem, my guess, from all the experiences i read about folks modding the lenco is that Lenco themselves did not realise the potential of their product ! the lenco sounds far better without the original plinth (nuded) than with it ..and that might be the reason many other designs overtook them.


furthermore the tonearm was another bottleneck to what it could do.

 

[jls001]

but the spindle extender with a acrylic platter is pretty tempting !

That's a low-hanging fruit. I think it is do-able without spending much. May be I should do this as a learner project.

I got a quote for the acrylic platter and it is reasonable (I think). Need to meet the lathe guy and see if he is up to it. I am assuming that this will also be reasonable (cost-wise).

Professional polishing will be needed to give it mirror-smooth finish. So one can machine it slightly larger than the final dimension and arrive at the final dimension by polishing. I am looking for a very close fit a la Jeremy's bearings. "Burn-in/Bed-in" will take care of the final mating. I hope

 

[prem]

Hi Arj

Most of the mods seem to be for mechanical reasons. I don't think too many electrical mods are done. I can understand new bearings being used as the older ones may have got worn out. But instead of building a new plinth and changing the damping characteristics would it make sense to place the table on something like an air bearing for isolation

 

[arj]

Hi Arj

Most of the mods seem to be for mechanical reasons. I don't think too many electrical mods are done. I can understand new bearings being used as the older ones may have got worn out. But instead of building a new plinth and changing the damping characteristics would it make sense to place the table on something like an air bearing for isolation

Apparently the main issue with the lenco is motor vibrations as it has a powerful motor, and if not managed well it causes rumble ..and hence it's demise in the past. The main reason for the new resurgence is due to what nantais found around draining those vibrations away and the best way to achieve that is via mass loading..the closer you get to infinite mass the better. Hence isolation which works great on other TTs does not have the same impact on an lenco unless it had a mass loaded plinth

Again by itself it is still a good table and punches above its price. But once you get it into a plinth and change the arm, it improves exponentially !

Regarding electrical..there is nothing to mod..the only thing electric is the wire which goes thru a switch into the AC motor ..rest of it all is mechanical..and that the beauty of this table !

 

[Norton]

Hi Joshua
Some great info back there....will use it to build my L75 plinth as well. thanks for sharing.
I am missing a good tonearm- where do you buy the ones you mentioned from

Cheers

 

[jls001]

Hi Joshua
Some great info back there....will use it to build my L75 plinth as well. thanks for sharing.
I am missing a good tonearm- where do you buy the ones you mentioned from

Cheers

For tone arms, please try ebay.com, eBay.co.uk, audiogon, lencoheaven.net.

For the L75, look for tone arms with 210 mm mounting distance (pivot to spindle distance). Besides mounting distance, you also need to consider whether the arm is a direct drop in or not. If you are ready to drill a new arm hole, arms with different mounting distances will also do.

 

[prem]

Hi arj

I am still confused. You are saying there is a lot of motor rumble which will generate a lot of vibrations. Heavy plinth is one way of absorbing the vibrations. Would not 4 well designed feet do the same? Is this not something similar to having a sand box with lead shots under speakers vis a vis well designed footers under the speaker?

 

[jls001]

Hi arj

I am still confused. You are saying there is a lot of motor rumble which will generate a lot of vibrations. Heavy plinth is one way of absorbing the vibrations. Would not 4 well designed feet do the same? Is this not something similar to having a sand box with lead shots under speakers vis a vis well designed footers under the speaker?

My limited understanding is that the motor vibration needs to be absorbed by mass. The higher the better. That is why most heavy-mass proponents insist on mating the pan of the top plate (the part below the platter) directly to the plinth below. More contact area means more conduction of vibration from the motor to the plinth (from motor --> top plate via three spring suspensions --> plinth). The top plate has a large area (all areas other than the area directly below the platter) that is not in contact with the plinth below. Only the vertical edges are in contact with the top layer of the plinth. So some people have gone to the extent of filling marine-grade epoxy onto the area that does not have contact with the plinth so that the top plate is imparted more rigidity when the epoxy hardens, as well as given a filler that will allow it to mate directly to the top layer of the plinth.

Another way of draining off the vibration is through feet that mates so a substantial mass below it.

An example here (a G301, not a Lenco, though. But the principles are similar): 6moons audio reviews: The Garrard Project Part 2: The Plinth

I tried finding more examples which I recall seeing in the past but I came up blank for the moment.

Yet another method is to use isolation of motor from the top plate. Only contact being via the rubber contact of the idler wheel to the platter. Here motor is supported from the equipment rack, independent of the top plate and plinth combination. It needs elaborate arrangement to ensure correct positioning and height so that the idler wheel touches both motor spindle and platter simultaneously. But even in this arrangement the common factor of equipment rack remains (much like an isolated arm pod being mounted on the same rack shelf as the turntable, thus negating some of the benefits of an isolated arm pod).

Also, to clarify further: the link I posted of Thomas Schick's website is only to illustrate the concept of a loose bearing (the picture with the two red arrows). It is not to imply in any way that the pictures are the final pictures of Mr Schick's Lenco rebuilds (if at all he did that). I am guessing he is is trying to show the three different types of Lencos he acquired. They don't even show the turntables using his famous tonearm!

 

[prem]

Hi jls001

Thanks for the detailed explanation. I understand what your are saying. While using a heavy mass for absorption is one option, my limited understanding tells me that there will be a way to dissipiate the vibrations in another way. Using a heavy plinth will only absorb the vibrations. Naturally the heavier, better the absorption. But as is the case with all kinds of absorption, some of the harmonics/nuances will get absorbed. Further the plinth resonance will come into the picture.

 

[arj]

Hi jls001

Thanks for the detailed explanation. I understand what your are saying. While using a heavy mass for absorption is one option, my limited understanding tells me that there will be a way to dissipiate the vibrations in another way. Using a heavy plinth will only absorb the vibrations. Naturally the heavier, better the absorption. But as is the case with all kinds of absorption, some of the harmonics/nuances will get absorbed. Further the plinth resonance will come into the picture.

I am sure there are ways to do that but will come it at some cost..so from a cost factor Mas loading might just be easier to do especially as most of the work around Lenco is done by DIY'rs and as a lower cost option

You are right about plinth resonance..hence the kind of plinth is very important. The most recommended is the Constrained Layer Damped plinth with Birch ply + MDF which together or Baltic Slate which are apparently the most effective. Most other Woods may add their own flavor to this but i presume that will come into play only after it has damped out the vibration of the motor which impacts the transparency and background noise

BTW folks have tried everything for Concrete to Lead with wood shaving for the plinth

 

[prem]

Hi Arj

Thanks. Yes mass loading would be the cheapest way

 

[jls001]

Hi jls001

Thanks for the detailed explanation. I understand what your are saying. While using a heavy mass for absorption is one option, my limited understanding tells me that there will be a way to dissipiate the vibrations in another way. Using a heavy plinth will only absorb the vibrations. Naturally the heavier, better the absorption. But as is the case with all kinds of absorption, some of the harmonics/nuances will get absorbed. Further the plinth resonance will come into the picture.

Yes, absorbing the vibration is one way of tackling unwanted vibrations. Draining it off would be another way. Isolation would be another method. In fact if one uses a heavy plinth with some kind of rigid coupling like a metallic cone below the plinth, one is doing both - the plinth absorbs the bulk of the vibration and turns it into harmless heat, and whatever vibrations is not absorbed drains through the cone to the equipment support, and then to the floor below.

For the specific case of Lenco heavy platter idler drives, the general consensus seems to be to use constrained layer damping, or at least a pseudo constrained layer damping. The material of choice seems to be baltic birch plywood. I think it is a hardwood found in colder climates. The advantage of CLD is that one gets a composite characteristic (e.g.: a resonant frequency which is different from that of the component parts).

Some of the nuances present in the record are definitely corrupted by the presence of unwanted vibration coming through to the platter, especially the finer nuances. This can result in lowered resolution and loss of microdynamics.

So the most critical thing is to lower any unwanted vibration from reaching the platter and tonearm assembly. BTW, tonearm resonance and reflection is another equally vexing subject

 

[shafic]

[QUOT BTW, tonearm resonance and reflection is another equally vexing subject[/QUOTE]

Can you explain? pls!

 

[prem]

Thanks jls001 once again. Someday I would like to listen to a fully modded Lenco. I had almost ordered one two years back from Nantais. Then someone pointed me to an EMT and that to me looked a more hassle free machine. So went for it

 

[Norton]

hi guys

I had picked up a Lenco L75 a while ago and was left neglected at my home for a while. a very beautiful TT to look at, however i was completely let down with the loud motor noise and crazy vibrations that ran through the tonearm. I had tried some DIY methods earlier which had failed. the TT was originally mounted on a Goodmans amplifier which was sold separately during the deal. yesterday, I sat down again and took it apart - lubricating the motor, spindle, spring suspension, etc. noticed that the TT had been imported a while ago and was running on the optional 110V on the power supply board-guess that's why the previous owner sold it off. i moved it to 220 and hey the motor is whisper silent- I am right now listening to Dire straits money for nothing with the plinth which inspite of a split state(no base-just side walls), the sound is truly outstanding and this is with the original tonearm whose v blocks haven't been changed. This TT is a killer and am going to make a real solid plinth. have recently seen a solid aluminium plinth housing a TD124, with a friend. might just end up replicating it.
My TD 124 has serious competition

 

[jls001]

Solid aluminium would be quite a plinth. There was a 124 sold by a gentleman in NCR a couple of years ago, with a plinth machined from a billet of solid aluminium. It would be a very interesting experiment to try something similar for the L75.

 

[captrajesh]

Solid aluminium would be quite a plinth. There was a 124 sold by a gentleman in NCR a couple of years ago, with a plinth machined from a billet of solid aluminium. It would be a very interesting experiment to try something similar for the L75.

How about using layers of Aluminium (say 10 mm layer) interspersed with stuff like acrylic?

 

[jls001]

How about using layers of Aluminium (say 10 mm layer) interspersed with stuff like acrylic?

Aluminium and acrylic have similar properties - both dampen vibration well. I think Artisan Fidelity uses a layer of what looks like aluminium sandwiched by what looks like solid wood planks (from YouTube videos). This is for their version of the 301 that sells for megabucks.

In my opinion, aluminium plus acrylic should work quite well. In fact when I started this build I was bent on mixing plywood, aluminium, acrylic, MDF and a rubber-type material to make it true constrained layer damping. Aluminium was discarded due to cost and difficulty of sourcing it. Rubber-type material was also discarded as I thought plywood plus MDF plus acrylic was sufficiently CLD.

 

[captrajesh]

Aluminium was discarded due to cost and difficulty of sourcing it.

At least in Chennai it is not difficult to source. In fact I have accumulated a few pieces of aluminium sheets of different thicknesses from 10mm to 4 mm which bought for making the F5 cabinet but the project is in hanging fire for quite sometime due to paucity of time. Do let me know if interested and I can PM you the details.

 

[jls001]

Some links you may find useful -

http://www.rgbronze.com/images/material-selection.pdf
Sintered Bronze Plain Bushes
Mumbai bronze bearings

Thanks, quad. I paid a visit to Bearing and Bush today. They are located in super crowded Nakodha Street in Pydhonie. Took some searching to locate them. Unfortunately, they did not have bushing longer than 30 mm though they have various inner dimensions and outer dimensions to choose from. Since I didn't know if I would find anything better, I ended up buying two pieces each of:

1) 12 mm inner dia with 18 mm outer diameter
2) 18 mm inner dia with 25 mm outer dia

These are made of sintered bronze, and as per the vendor (they are manufacturers who, luckily for me, sell in retail quantities) it is self lubricating. I bought two pieces each with the hope that I will figure out some way of joining them together to form a single bushing.

I consulted magma further and he directed me to Nagdevi Street in the same area. I walked to Nagdevi Street and started searching again. A shop selling ball bearings directed me to go search in Gullalwadi. After near missed connections, I found the motherlode. Came back with sufficient lengths of brass piping.

a) first one is 16 mm inner dia with 25 mm outer dia
b) second one is 19 mm inner dia with 32 mm outer dia

The walls are satisfyingly thick .

Now to design a bearing for the L75. My plan is to make two bearings - one for one-platter operation, and the second for stack platters.

I have doubts on how best to design the bottom part of the bearing as well as the thrust pad (the load bearing part). I do have some thoughts, mainly how to keep it simple, but I am not yet sure if it will be workable. I will tap the collective brain of the forum for more ideas and validations of thoughts.

For perspective: stock L75 bushing inner dia is nearly 9 mm (about 8.95 mm) and the bearing diameter is about 8.85 mm, so it is a very tight fit. Meaning my bushing is hardly worn. It even passes the "Schick Test" with flying colours.