[ACHiPo]

Yep, I'm definitely off the deep end (or ever deeper into the rabbit hole), as I have a new project--building a turntable.  Actually, I'm going follow lots of others that reuse key parts of a Lenco idler-drive turntable to take them to a new level of performance by replacing the sprung plinth with a massive hunk of something to damp vibrations while rigidly coupling the spindle to the tonearm.

My adventure started when I stumbled across this article by Arthur Salvatore.  While I'd heard about (and lusted after) the Forsell and other decks he referenced, I'd never heard of a Lenco.  To see his claims that a turntable that could be purchased for a few hundred bucks (less in Europe) could best statement turntables captured my imagination. 
http://www.high-endaudio.com/RC-Lenco.html

Over the next few months I continued to research what I could about idler drives--something that was old and rumbly when I got into hi-fi in the 70s as everyone was into belt drive and direct drive.  I discovered the Thorens 124, and Garrard 301 and 401, all of which were much more expensive with rarer replacement parts.

A few weeks ago I found this 60 Hz deck for $300 (AC frequency is important, as most Lencos were built for 50 Hz, and the higher US frequency creates a challenge with running at 33.3 RPM).  The tonearm was trashed, but I didn't care since I'd be adding my own (maybe 2!).  I took a gamble and hit "buy it now".  The seller warned me that the packing was in rough shape, but that it would arrive safely, and he was correct on both counts.










The seller had correctly tightened the transport screws to protect the motor suspension, and removed the platter for shipping.

I plugged it in and it spun.  There was a bit of noise, but I expected that since it was an old idler drive--it likely needed a full rebuild.  I moved my second arm on its pod over to the Lenco and aligned it with the Feickert protractor, using Adjust+ to dial in azimuth and VTA.  There was no mat, but I wanted to see how it sounded, so I put on a record.  Tada, music.  Yes there was a bit of rumble, but it sounded pretty darned good.  Sitting there listening to music coming out, I remembered that I forgot to LOOSEN the transport screws!  Removing the platter, I loosen the 3 red screws, replace the platter and put on a record again.  Dead quiet!  Magic!  I now know what all the shoutin' is about--this thing as-is compares quite favorably to my WTT Reference turntable.  Now I'm excited!

[TomS]

Very nice. I assume you know about these guys already, lots of good advice there http://www.lencoheaven.net/

For a plinth, consider the benefits of a nice slab of blue slate, which is what my rim drive TT uses. Good stuff, readily available, very stable 

[orientalexpress]

sweet,i got a lenco laying around also.maybe this will motivate me to start a project,can't wait to see what you do to it.

[ACHiPo]

Very nice. I assume you know about these guys already, lots of good advice there http://www.lencoheaven.net/

For a plinth, consider the benefits of a nice slab of blue slate, which is what my rim drive TT uses. Good stuff, readily available, very stable 

Tom,
Yep, I've been spending a lot of time learning about Lencos and looking at design concepts on LH.  Slate is one possibility, as are soapstone and traditional laminated wood, but right now I'm leaning toward a resin and bentonite plinth.  More on those musings later.

AC

[Maceo23]

I built my PTP4 Lenco a couple of years ago and still absolutely love it.  I built it using 6 layers of 1/2" Corian.  Very heavy, and easy to cut with wood working tools. 

[SteveRB]

Last table I plan to own. I ordered from Peter last year: a Solid12.

[FullRangeMan]

Nice arm, I suggest use 2 or 3 arms for MC and MM if table room allow.

[ACHiPo]

I considered a PTP, as well as Corian.  For this build I'm going to use as shaved top-plate "frying pan", although mine will be more like an "amoeba" since I plan to leave the on/off switch in place as well as the speed control selector.

I've already ordered and received one of Norbert's idler wheels,
http://www.lencoheaven.net/forum/index.php?topic=11628.210

as well as after-market PTFE bushings and a brass clamp to replace the circlip on the idler shaft.
http://www.lencoheaven.net/forum/index.php?topic=21002.0

I've ordered a spindle bearing cap to replace the plastic one, and allows the spindle bearing to be bolted to the plinth.
http://www.lencoheaven.net/forum/index.php?topic=9739.150

I also have a pair of VibroStop Platter Mats stacked on the Lenco (I'm really liking them so far, at least as compared to no platter mat):
http://www.hologramacoustics.com/product/vibro-stop-platter-mat/

The rest of the mechanicals will just be taken apart and cleaned/lubed.  My hope here is to not screw something up, as the current performance is pretty darned good as-is.

Here is the concept for my turntable:



The Lenco top plate will be rotated 90° counter clockwise so the on/off switch will be ~1:00.  The Pioneer PA-70 tonearm will be ~2:00, and I'll be adding a TransFi Terminator linear tracking tonearm at 12:00, angled at ~30° which should make it relatively easy to access for operation and stylus cleaning.  The Pioneer will have multiple headshells/cartridges, but will primarily be for my Miyajima Zero mono cartridge.  The TransFi will have two interchangeable arms, one with a Lyra MC and one with an AT 150 MLX MM cartridge.

Key design considerations for the plinth are to 1) reduce vibration by servicing and tuning the motor, idler, and spindle bearing.  2) isolate/damp motor and idler, 3) rigidly couple the spindle bearing to the tone armboards, and 4) damp the tonearm/spindle coupling by sinking internal vibrations to the plinth, 5) massive, high-damping plinth to absorb internal and external vibrations.  I may also add a second platter to add rotational inertia and deal with the relatively low platter height of the Lenco.  I will use armboards to allow for future arm changes made from either Panzerholz, cast resin/bentonite, or baltic birch plywood.

[ACHiPo]

The leading candidate for plinth material is bentonite (fancy kitty litter--unused  ) saturated into isopthalic polyester resin as formulated by Rap,
http://www.lencoheaven.net/forum/index.php?topic=12943.msg196263#msg196263
 and used by others. 
http://audiokarma.org/forums/index.php?threads/resin-bentonite-clay-plinth-build.530544/
http://www.lencoheaven.net/forum/index.php?topic=14351.0

I looked at Panzerholz, which has a great reputation for good damping properties (plus it's bulletproof for those Hunter Thompson moments )
http://www.delignit.de/Delignit/cms/front_content.php?idcat=17&idart=46&changelang=3

It's also hard to find and really expensive when you do (~$1kUSD for ~3' x 5' sheet ), which is why I'm considering teaching myself to cast polyester kitty litter.

As I mentioned I'm also considering soapstone and possibly slate, although working those materials I find even more intimidating than learning how to cast and finish resin.

[Bob2]

Nice project. I did the same thing with a Thorens.. I'm very happy with the results as I'm sure you will be.

[neobop]

It's also hard to find and really expensive when you do (~$1kUSD for ~3' x 5' sheet ), which is why I'm considering teaching myself to cast polyester kitty litter.

As I mentioned I'm also considering soapstone and possibly slate, although working those materials I find even more intimidating than learning how to cast and finish resin.

Hi Evan,
Nice project.  We're at approx. the same point in our plinth projects.  In other words, I haven't really started on my TT81 build, but I've been thinking about it.  I suggest you consider resin and ground limestone.  That's what Kenwood used for the anti-resonant  material in the KD500/600 and LO7D.

Limestone is heavier than kitty litter and might be better?   I've been considering layers of different materials.  When you add a substance to the resin it reduces the flow of uncured material, so it might be possible to build up a plinth w/o a complete mold. 

Thanks for starting this thread.  Let us know how it goes.
neo

[ACHiPo]

Hi Evan,
Nice project.  We're at approx. the same point in our plinth projects.  In other words, I haven't really started on my TT81 build, but I've been thinking about it.  I suggest you consider resin and ground limestone.  That's what Kenwood used for the anti-resonant  material in the KD500/600 and LO7D.

Limestone is heavier than kitty litter and might be better?   I've been considering layers of different materials.  When you add a substance to the resin it reduces the flow of uncured material, so it might be possible to build up a plinth w/o a complete mold. 

Thanks for starting this thread.  Let us know how it goes.
neo

Neo,
Thanks!  I'm struggling to find the comparison of damping at acoustic frequencies, but here is a pretty good discussion on the merits of the bentonite/resin system (skip about 2/3s down until you get to "Rap", Hrappur Magnusson who is a published seismic geologist and seems to really know his stuff, and continue on to the 2nd page:
http://www.vinylengine.com/turntable_forum/viewtopic.php?f=18&t=56141

(I just found one of the posts with damping factor data:  http://lenco.reference.clicforum.fr/t551-damping-factors.htm)

The resin+ground limestone idea is interesting as well, as it should have similar performance to Corian or Silestone.  From what I've been able to fine, the bentonite mixture is superior to both, but obviously people have made very good sounding turntables out of both materials, so it may not matter all that much.  Also, the data I've found to data are results published in forums, not in refereed journals, so there may be significant errors in the results.  I do trust what I've read of Rap's explanations, however, so therefor am leaning in that direction.

Check out this build from Rap.  I really like the steel skeleton frame, and the finished product is very nice looking.
http://lenco.reference.clicforum.fr/t2198-Donc-je-recommence.htm?q=rap

[ACHiPo]

Made it to Kinkos to get the template printed out.  The template is designed for A1 paper, but prints well on 24" x 36" paper here in the states.  Started by checking the TransFi tonearm placement.  It think it will work quite nicely.  By the way, I'm very impressed with the fit and finish of the TransFi tonearm.  I hooked up the air pump and quickly determined that the tonearm wasn't level as the carriage slid toward the end.  A quick twist of the alignment thumb screws remedied the problem.  Seems like it will be pretty straight forward to dial in.

Once I got the TransFi pretty much situated, I placed the Pioneer PA-70 tonearm to make sure everything would still play nicely with each other.  Looks like it will.



Now that I have the alignment pretty much figured out, it's time to strip the Lenco down.  I'll be cutting down the top plate so that it fits flush into a 22 mm deep cavity.  Of course that means I need to find/make a 22 mm thick top to my plinth.  I'm still noodling on that one.


The bearing was dry, but the bottom cap is in good condition--not that it matters all that much as I'll be replacing the bottom cap with a machined piece that's threaded for additional bracing from the bottom.  The spindle seems to be in good condition.  I've got a replacement Si3N4 ball bearing for the bottom, as well as a new PEEK thrust plate.





The top plate is all stripped down and ready for trimming to size.  That's a task for next weekend.

[ACHiPo]

Hi Evan,
Nice project.  We're at approx. the same point in our plinth projects.  In other words, I haven't really started on my TT81 build, but I've been thinking about it.  I suggest you consider resin and ground limestone.  That's what Kenwood used for the anti-resonant  material in the KD500/600 and LO7D.

Limestone is heavier than kitty litter and might be better?   I've been considering layers of different materials.  When you add a substance to the resin it reduces the flow of uncured material, so it might be possible to build up a plinth w/o a complete mold. 

Thanks for starting this thread.  Let us know how it goes.
neo

Neo,
Have you made any more progress on a plinth?  I'm talking myself out of trying to cast one, as the thought of making a mold turns my brain inside out, so I'm back to alternating MDF and birch ply with some sort of elastomeric glue.

AC

[WGH]

I looked at Panzerholz, which has a great reputation for good damping properties (plus it's bulletproof for those Hunter Thompson moments )
http://www.delignit.de/Delignit/cms/front_content.php?idcat=17&idart=46&changelang=3

It's also hard to find and really expensive when you do (~$1kUSD for ~3' x 5' sheet ), which is why I'm considering teaching myself to cast polyester kitty litter.

Take a look at Richlite, it is also compressed wood similar to Panzerholz. Richlite can be machined with carbide tools and is readily available, if you are lucky a local distributer or installer will have samples or scraps like sink cutouts to play with.
http://www.richlite.com/



Here is my un-scientific tap test of three materials including Richlite:
https://www.youtube.com/watch?v=SkSxH40x5SA

Search for "Richlite" on AC, I have made many posts over the years with my damping experiments.

Wayne

[ACHiPo]

Wayne,
Thanks for the tip!  I've sent an email to Richlite and their distributor in Northern CA.

AC

[neobop]

Neo,
Have you made any more progress on a plinth?  I'm talking myself out of trying to cast one, as the thought of making a mold turns my brain inside out, so I'm back to alternating MDF and birch ply with some sort of elastomeric glue.
AC

No, not really.  I'm working on another long term project, unrelated to audio.  It's slow going because I don't know what I'm doing.

IMO you're overthinking this damping/vibration transmission factor.  Based on results from other tables, it's high mass or weight which is the primary source of solid sound.   Consider the Saskia idler.   The slate plinth weighs 200 lbs.  Slate is a good transmitter of vibrations, but it doesn't seem to matter.
The mass of the plinth turns low amplitude vibrations to heat and is better able to resist movement.

The combination of different materials tends to cancel resonances.  You could have some slate cut like the TransFi table, and/or incorporate different materials like lead.  Filling cavities with sand might be another possibility.  High mass and rigidity seems to get it.

You already have a plinth you can use as a basis for a mold?  Instead of a traditional mold, augment what you have.  If you mix ground stone with epoxy or resin, it won't run like a thin liquid.  Use some sheet metal around the main cut-out hole and outer edges.  Spray exposed surfaces of the mold with cooking spray for mold release.  You could build it up in layers.  Incorporate any threaded inserts (feet or chassis attachment) in the appropriate layers of your mold.  That's what I've been thinking.  I'll probably have a couple of layers of sheet lead. 
neo



 

[ACHiPo]

No, not really.  I'm working on another long term project, unrelated to audio.  It's slow going because I don't know what I'm doing.

IMO you're overthinking this damping/vibration transmission factor.  Based on results from other tables, it's high mass or weight which is the primary source of solid sound.   Consider the Saskia idler.   The slate plinth weighs 200 lbs.  Slate is a good transmitter of vibrations, but it doesn't seem to matter.
The mass of the plinth turns low amplitude vibrations to heat and is better able to resist movement.

The combination of different materials tends to cancel resonances.  You could have some slate cut like the TransFi table, and/or incorporate different materials like lead.  Filling cavities with sand might be another possibility.  High mass and rigidity seems to get it.

You already have a plinth you can use as a basis for a mold?  Instead of a traditional mold, augment what you have.  If you mix ground stone with epoxy or resin, it won't run like a thin liquid.  Use some sheet metal around the main cut-out hole and outer edges.  Spray exposed surfaces of the mold with cooking spray for mold release.  You could build it up in layers.  Incorporate any threaded inserts (feet or chassis attachment) in the appropriate layers of your mold.  That's what I've been thinking.  I'll probably have a couple of layers of sheet lead. 
neo

Neo,
No doubt I'm over thinking it--it's what I do --further exacerbated by f'ing up my wonderful and very expensive and even harder to install balanced IC under my floor to my amp last weekend while rearranging gear on my rack to make room for my new phono stage.  Gives a guy pause to "measure twice, cut once", except I seem to take it to an extreme and overthink 400 times!   So while I figure out how to pull the IC out from under the floor so I can send it back and hopefully get repaired and still be long enough to work I'll continue thinking about how to make a "good-enough-for-reference-quality" plinth.

Analysis paralysis is one reason I'd pretty much just decided to build what I think will be pretty good, and that is a massive wood plinth, for which I've already got the materials and template (and skills and tools).

To be continued...

AC

[neobop]

I suspect it will be pretty damn good whichever way you decide to go. 

I'm thinking of alternatives to traditional casting and it seems to be layering without a complete mold.  It would be relatively easy for you to use what you've got and make a layer(s) of heavier material. 
neo

[WGH]

Instead of a traditional mold, augment what you have.  If you mix ground stone with epoxy or resin, it won't run like a thin liquid.

Casting epoxy will need a lot of experimenting, when epoxy cures it produces a lot of heat because the two chemicals react in an exothermic reaction. Too much heat and the epoxy will boil and foam.

I use a lot of epoxy and buy it in 5 gallon containers from West System http://www.westsystem.com/ss/ Check their Where to Buy list for a local distributor.
The company does extensive testing and could advise you how to cast epoxy, I have called tech support many times and they are friendly and helpful.

West also sells epoxy additives and thickening agents. Mixing in colloidal silica can make the epoxy as thick as peanut butter if you want and as hard as quartz.
http://www.westsystem.com/ss/406-colloidal-silica/