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Building a Plinth for Lenco L75

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Old 29th February 2012, 10:17 AM
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Building a Plinth for Lenco L75


It's been a long, long time since my Lenco L75 gathered dust in a forgotten corner of the house. It has been silently crying out to be transformed into (hopefully) a beatiful swan.

I got the plans for the cutout from here in Lencoheaven (note: in case you need one, send an email requesting a plan for non-commercial, DIY usage). This template has to be printed to scale on an A1 sized page. In may case, one dimension matched exactly but the other dimension of my print was longer by 5 mm. I checked for slacks in the top plate and decided this is not serious enough so went ahead with it.

This single page plan contains the design for all layers, plus instructions on how go about building the plinth. It also contains important information on what parts to modify on your Lenco L75. It is a 6-layer design - layers 2 to 6 are 18 mm, layer 1 thickness may vary depending on your model of Lenco. In my case, I measured 10 mm.

The first important thing in building a plinth is to decide the outer dimensions. Since 2 foot sized boards are easier to get than smaller sizes, I bought 2' x 2' boards, and from there decided on the final length and breadth for the plinth. Considering that the CLD plinth for my TD124 is 22" wide and about 16 an 1/2", and offset to one side leaving space for longer tonearm on one side (wrong side, actually since the extra space is next to the tonearm), I decided to center the turntable on the plinth in the left-right dimension so that space is there for an extra arm (or two). Since I won't be using the front of the 'table to mount an arm, I decided to leave just 2 inch of space in the front and about 4 inches to the back. With this consideration, I arrived at 23 inch x 19 inch. It is fairly big and quite heavy.

Next decision was what materials to use for the layers. The design from Lenco Heaven is a pseudo-CLD for Baltic Birch plywood of 18 mm thickness. I decided to be a bit more adventurous and started searching for available materials. I found a shop selling tons of acrylic sheets of various thicknesses and shades. The required 18 mm thickness was available, but I decided to go one step further and use two layers of 10 mm acrylic. I couldn't get aluminium sheet so I decided to simply stick to plywood and MDF for the remaining layers. Sandstone is still a future option as the bottom most layer as it will not require any fancy-schmancy cutouts except for the outer cuts.

Below are some pictures of the work in progress.

1. The layers cut to 24" x 24" and marked.



2. The sheets stacked up - thickness is bit more than 3 and half inch. The layers are 18 mm marine grade plywood, 17 mm MDF sheet, 2 layers of 10 mm clear acrylic sheet, 18 mm marine grade plywood, and 17 mm MDF sheet - this is not the final order of the layers.



3. Marking round edges:



4. Drilling guide holes to insert saw bit. The saw bit is really slim and has very sparse teeth but cuts like a demon possessed. The acrylic sheets were quite hard and and two saw bits bit the dust. Plywood was easier and MDF was a cakewalk.



5. The second layer being cut - note the blurry movement of the sawing machine. The guy who did the cutting was really skilled as his daily job is to cut intricate designs on wood, plywood or MDF sheets. The accuracy of the cuts boiled down to how accurately I had marked the cut out lines.



6. Assembling the layers after the cut. The greenish top layer is 10 mm thick water-proof MDF and it turned out to be much harder than the 17 mm MDF boards I had bought earlier. I had not bought the top layer as I did not have the thickness measurement. As I was stepping out from the workshop to a nearby plywood store, the workshop owner offered me this green MDF. As it was of the right thickness and looked rather fancy, I decided to use it.



7. The layers in proper sequence. Top to bottom: 10 mm MDF, 18 mm plywood, 17 mm MDF, 10 mm acrylic, 17 mm MDF, 10 mm acrylic, and 18 mm plywood.



8. Here's a view of the cavity for the sizable motor:



9. The whole assembly:



Next steps:

1. I am awaiting the arrival of the Origin Live Silver III tonearm to modify the tonearm base of the Lenco L75

2. I am also awaiting the arrival of an SME 3012 arm from Delhi to decide on the position of second arm base. This was not part of original plan but since the layers are not yet glued together, it can still be done easily.

3. Gluing will happen only after step 2 above.

4. Need suggestions on which MC cartridge to buy, beside the Denon DL 103R. Can't spend too much here.

Will update with pics as the project progresses.
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Old 29th February 2012, 12:01 PM
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Re: Building a Plinth for Lenco L75

Super job done so far Joshua

Eagerly waiting for next installments of the build. I for one will most certainly like to come over to listen to the L75, once its ready to 'play'

Certain amount of nostalgia associated to the L75, due thanks to my late uncle having one (his pride & joy)

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Old 29th February 2012, 03:27 PM
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Re: Building a Plinth for Lenco L75

Neat looking job Joshua.

Yes acrylic is little difficult to cut. It melts and burr grips the saw bits.
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Old 1st March 2012, 08:18 AM
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Re: Building a Plinth for Lenco L75

Quote:
Originally Posted by jls001 View Post
4. Need suggestions on which MC cartridge to buy, beside the Denon DL 103R. Can't spend too much here.
whats you budget.,
I really feel DL103 is highly underateed ! it is very involving,although not as detailed as the R version (which may be a good thing !)

what is the Phono you pan to use you need atleast 50 db of gain for the 103...
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Old 1st March 2012, 08:37 AM
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Re: Building a Plinth for Lenco L75

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Originally Posted by jls001 View Post
4. Need suggestions on which MC cartridge to buy, beside the Denon DL 103R. Can't spend too much here.

Will update with pics as the project progresses.
You can also consider SAE 1000E HOMC SAE 1000 E | eBay

Regards,
Sachin
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Old 1st March 2012, 08:38 AM
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Re: Building a Plinth for Lenco L75

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Originally Posted by arj View Post
whats you budget.,
I really feel DL103 is highly underateed ! it is very involving,although not as detailed as the R version (which may be a good thing !)

what is the Phono you pan to use you need atleast 50 db of gain for the 103...
More details emanating from my analog rig would be highly welcome

Current phono is Musical Surroundings' Phonomena. It handles both MC and MM and has various capacitance loading options. I have not really checked whether it has gain settings as I have been using it only with MM. Second MC only phono pre will be Ortofon MCA 76. Third (MC only) will be the DIY MC phono pre being organised by Sachin.

I don't have a working MC cartridge at this time. I do have an Ortofon MC20 with a broken cantilever with the stylus chopped off. I am mulling whether it's worth a retip at Soundsmiths (at about $250+), or whether I should trade it for another cartridge at Ortofon (about $65 discount on whatever one buys). I am thinking option 1 may be the more worthy option since the current avatar of the MC20 (in Super form) is fairly highly rated and costs quite a bit of coins (the dollar kind).
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Old 1st March 2012, 10:02 AM
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I'd second the denon 103 joshua especially since you're getting the SME.

Plinth is shaping up lovely! One thing I wanted to ask. My current understanding is that dissimilar materials cut off vibration at the intersection so in your multiple type plinth vibration will drain from the table and end at the first 18mm layer where it meets another material whereas with a continuous material it would have a many more similar drainage layers to dissipate in. Some expert can chime in...

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Old 1st March 2012, 11:19 AM
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Re: Building a Plinth for Lenco L75

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Originally Posted by stevieboy View Post
I'd second the denon 103 joshua especially since you're getting the SME.

Plinth is shaping up lovely! One thing I wanted to ask. My current understanding is that dissimilar materials cut off vibration at the intersection so in your multiple type plinth vibration will drain from the table and end at the first 18mm layer where it meets another material whereas with a continuous material it would have a many more similar drainage layers to dissipate in. Some expert can chime in...
One of the inspirations of using multiple materials sandwiched together is this: Clearaudio Innovation Wood Turntable w/ Universal

Note that the Innovation uses thin layers of aluminium and thicker layers of panzerholz. The latter is unobtainium.

My understanding too is that sandwiching materials with different vibration damping characteristics produces a composite characteristic, which will - hopefully - be better than the sum of the component parts.

Plywood seems to be universally acknowledged as having good damping characteristics due to it being built of thinner layers glued together. I guess the same explanation holds true for slate which also has inherent layers. On the other hand, MDF which is nothing but a composite of wood particles is said to ring (when used on its own). At the other extreme, panzerholz which is nothing but a highly compressed MDF is supposed to be as good or even superior to aluminium, the acknowledged king of the plinth material hill (I think). In between there are many others - hard woods like ebony (especially the Coromandel and the Macassar varieties), mahagony, teak, etc, synthetic materials like acrylic and delrin, and various natural stones like slate, granites, marbles, etc. I have heard of folks even casting them in concrete!

So I guess the hope here is to imbibe the best virtues of the component materials, and (again, hopefully) eliminate the harmful sides.

The easy and cheap option would have been to simply use layers of plywood.
Joshua
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Old 1st March 2012, 01:37 PM
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Re: Building a Plinth for Lenco L75

Quote:
Originally Posted by stevieboy View Post
I'd second the denon 103 joshua especially since you're getting the SME.

Plinth is shaping up lovely! One thing I wanted to ask. My current understanding is that dissimilar materials cut off vibration at the intersection so in your multiple type plinth vibration will drain from the table and end at the first 18mm layer where it meets another material whereas with a continuous material it would have a many more similar drainage layers to dissipate in. Some expert can chime in...

Regards


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there is another way of looking a this. Each material has different damping frequency (ie it damps a different frequency range). if they are layered together and glued well, the overall structure damps the entire range ie sum of all parts.
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Old 1st March 2012, 04:01 PM
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Re: Building a Plinth for Lenco L75

Getting complete rid of mechanical vibration and natural resonance is very difficult. Different materials dampens different fqs. Mechanical Vibrations are best reduced from dense material to less dense. Volume of material also helps. As also point of contact helps in stopping it from travelling from one medium to another. To find natural resonance of material I think one can measure it by placing a speaker on material and play all frq. range and measure on oscilloscope by placing a mic. Natural resonance of material will show as a peak.
Have been browsing a lot for these things. And had lots of links. But my google chrome bookmark/preferences file got corrupted. But here is interesting link with animation
Acoustics and Vibration Animations
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