New plinth project for Lenco L 75

[kuruvilajacob]

Hi Folks,
I love making plinths for heavy idler wheel Turntables. As my friend got a beautiful Lenco L 75 and Audio Technica AT 1007 Tone arm from Australia, he requested me to make a plinth for him as he was highly impressed with my Lenco plinth with Ortofone tone arm. I got a very talented young carpenter who managed making the plinth in 4 hours! Of course, he had the plinth design from my Lenco plinth and finished the working in no time. The original Tone arm is going to be removed and I am planning to cut out the corner from where the arm is removed so that the cosmetics will be intact. Then build a Teak wooden base for the Audio Technica arm to cover the cut out portion and laminate the entire plinth with Mahogany veneer. It should look grand when finished. Now for some pictures of work done till now

 

[peace_sells]

Just a slight off topic, basic question. As i understand, the plinth of any turntable should be made such that the entire system attains (close to) critical damping (neither under-damped nor over-damped..basically to eliminate rumble). So how does one know that a certain plinth will be right for a TT? How does one know that the plinth has not over-damped the system (people keep saying that the plinth should be heavy. Why is it not wise then to bury the turntable at the top of Mt. Everest?..sorry for the exaggeration but you get the point)? Sorry if I've asked a very trivial question but I want to get this clarified.

If you guys can direct me to some other thread where i can get this doubt cleared, I'd like that too.

 

[kuruvilajacob]

Just a slight off topic, basic question. As i understand, the plinth of any turntable should be made such that the entire system attains (close to) critical damping (neither under-damped nor over-damped..basically to eliminate rumble). So how does one know that a certain plinth will be right for a TT? How does one know that the plinth has not over-damped the system (people keep saying that the plinth should be heavy. Why is it not wise then to bury the turntable at the top of Mt. Everest?..sorry for the exaggeration but you get the point)? Sorry if I've asked a very trivial question but I want to get this clarified.

If you guys can direct me to some other thread where i can get this doubt cleared, I'd like that too.

I am happy to clarify to the best of my knowledge from my practical experience. Usually, idler wheel system produces a lot more rumble noise due to the friction from the platter and the motor of such players also make more noise than Direct Drives and Belt Drives. Presumably, because idler wheel players were made during a period when ceramic cartridges were being used more than magnetic. In ceramic pick up, the sensitivity of pick up needle was low and manufacturers of Idler wheel players were not paying much attention to rumble and motor noise as these were not critical. Later on, these Idlers became popular because of their high torque but the rumble noise while using sensitive magnetic MM and MC was a limiting factor. This made it necessary for damping these players to reduce the rumble noise and the idea of building huge plinth for such players is to ensure maximum rumble elimination. Now this will again depend on the material used for making the plinth. Marine ply is kept to be good for absorbing unwanted sound as they are layered and noise gets easily absorbed so that when the pick up stylus touches the record, there should be least noise from the idler wheel and motor. That's why such plinths are usually done for Garrard 301,401, Lenco L 75 etc. I hope I have been able to explain your doubt.

 

[jls001]

High torque motors, while they have their known advantages, produce more vibration. That vibration is transmitted to the top plate, platter and the tonearm. On conventional boxed plinths, the vibration was not suppressed, thereby producing rumble. When a high-mass plinth is used, it absorbs a good chunk of the vibration, thus minimising the rumble, and improving the sound reproduction.

How much mass is enough mass? That's difficult to say. But the accepted wisdom seems to be heavier is better, as far as the Lenco L75 is concerned. The Jean Nantais Reference model has a plinth weighing 100 lbs (45 kgs?).

On the other hand, the Loricraft plinth for the Garrards is not a heavy one but supposedly works very well too (I haven't heard one so I don't have first-hand knowledge).

In my unscientific opinion, about 15 to 20 kgs plinth for the L75 is desirable.

 

[G401fan]

The original manual and spec sheet of the Garrard 301 says: Rumble - negligible.

That's been my experience too. The motor on the 301 and 401 is suspended on 6 springs, which effectively filter away motor vibration. However, if the motor spindle has some play in it, that would be conveyed via the idler wheel into the platter. Likewise the main bearing. If you have a well maintained 301/401 which has good bearings, there's not much to worry about. I don't have experience about the L75 to comment about it.

In my opinion, the plinth damping issue for the 301/401 is over rated. It's just given room for some niche plinth makers all over the world to set up their little cottage industries.

 

[kuruvilajacob]

The original manual and spec sheet of the Garrard 301 says: Rumble - negligible.

That's been my experience too. The motor on the 301 and 401 is suspended on 6 springs, which effectively filter away motor vibration. However, if the motor spindle has some play in it, that would be conveyed via the idler wheel into the platter. Likewise the main bearing. If you have a well maintained 301/401 which has good bearings, there's not much to worry about. I don't have experience about the L75 to comment about it.

In my opinion, the plinth damping issue for the 301/401 is over rated. It's just given room for some niche plinth makers all over the world to set up their little cottage industries.

The quality of the idler wheel will also be a factor for 301 and 401 . The rumble may be negligible when the Turntable is new but after more than 50 years old, it may not be negligible unless it is well maintained . So the plinth mass can be a factor for older 301 and 401. For Lenco L 75, the mtor is much more silent when compared to 301 and 401 and idler wheel is thinner and vertical . In my opinion, Lenco L 75 may need only lighter plinth compared to 301 or 401. I may be wrong. T

 

[G401fan]

A worn idler wheel, or one that is not true, will more likely lead to speed variations, rather than increase rumble. To my knowledge, rumble is associated with motor noise, which, if present, would convey itself regardless of the quality of the rest of the chain. That said, the idler wheel, being of rubber, also is a dampener of vibrations to some extent.

Plinth experimentation makes more sense in the holistic context of the entire TT subsystem - including the arm, cartridge and mat. The signal from the cartridge is damped, or made more alive, based on some of these variables, which would change depending on the design of arm - pivoted, unipivot, high mass, etc - and likewise the cartridge, MM or MC, high VTF or low, and so on. Some high mass plinths, supposedly intended to absorb vibration, end up sounding acoustically dull. Similarly, lightweight plinths can sometimes sound too bright, or too 'hard'. A good mat makes a major difference - felt for the Linn, thick rubber for idlers. Footers also do matter, and sometimes cones change things too. Unfortunately most of us are not in a position to test multiple options, so we go with our gut instincts, or with received wisdom, and live with one or the other option.

 

[jls001]

....Plinth experimentation makes more sense in the holistic context of the entire TT subsystem ....

Totally agree with the "holistic context" part. There are mind-bogglingly diverse paths one can choose to tread to arrive at our own little (analog) audio paradise. Sometimes, going down one path precludes treading others.

Turntable improvement is not a one-note song (in a manner of speaking), nor is it a one-man concert. It is the sum of many small improvements. It is sometimes surprising what new doors one choice can open up or shut, effectively restricting, or opening up, the next set of choices and possibilities.

For example, if one chooses a low mass arm, one is forever stuck to high compliance cartridges. IMO, a good mid-way point is to use a mid-mass arm which can handle both high and mid compliance cartridges. On such a tonearm, headshell spacers and extra heavy counterweights can be added to play low compliance MCs.

There are many more examples.

 

[reubensm]

The quality of the idler wheel will also be a factor for 301 and 401 . The rumble may be negligible when the Turntable is new but after more than 50 years old, it may not be negligible unless it is well maintained

Agree with this observation as I have experienced it first hand with the Garrard RC210 changer. A slightly worn idler produces rumble. A new idler usually is silent.

The key to idler preservation is to have the idler disengage after play, ensure that the idler is not exposed to the elements (if in storage) and is kept free from dust, moisture and lubricants when mounted.

 

[reubensm]

Some high mass plinths, supposedly intended to absorb vibration, end up sounding acoustically dull. Similarly, lightweight plinths can sometimes sound too bright, or too 'hard'. A good mat makes a major difference - felt for the Linn, thick rubber for idlers. Footers also do matter, and sometimes cones change things too. Unfortunately most of us are not in a position to test multiple options, so we go with our gut instincts, or with received wisdom, and live with one or the other option.

How do these multilayered plinths perform, just as G401fan, I've consulted with a few friends who have used this approach and some of them did mention over dampening. Assuming your 401 is mounted on a multi-layered plinth, have you noted any drop in the punch factor? Many have advised me not to go too heavy on the L75 plinth. Again, I must consult with Mr. Kuruvila before giving it some thought as my knowledge on this front is very basic.

 

[reubensm]

found this plinth build (for a TD124) with some amazing level of skill: Building a Plinth -- TD-124 - AudioKarma.org Home Audio Stereo Discussion Forums

 

[sachu888]

Hi Reubnsm
You will need a heavy plinth for your Lenco.

Regards
Sachin

 

[kuruvilajacob]

Once I experimented with Slate plinth for Garrard 301 and it sounded dull and lifeless. I agree with G401fan that some plinths can be an 'overkill'. But for 301,401 or L 75 heavier multi-layered plinths should absorb vibration without much damage to reproduction. I always take such steps instinctively and only the slate plinth has been a disappointment for me so far

 

[kuruvilajacob]

How do these multilayered plinths perform, just as G401fan, I've consulted with a few friends who have used this approach and some of them did mention over dampening. Assuming your 401 is mounted on a multi-layered plinth, have you noted any drop in the punch factor? Many have advised me not to go too heavy on the L75 plinth. Again, I must consult with Mr. Kuruvila before giving it some thought as my knowledge on this front is very basic.

Rueben,
You can listen to my modified Lenco L 75 first and decide how you want to go forward with your plinth project after that. Please let me know the date you are likely to come so that I can keep that day free for you

 

[cat's squirrel]

Just a slight off topic, basic question. As i understand, the plinth of any turntable should be made such that the entire system attains (close to) critical damping (neither under-damped nor over-damped..basically to eliminate rumble). So how does one know that a certain plinth will be right for a TT? How does one know that the plinth has not over-damped the system (people keep saying that the plinth should be heavy. Why is it not wise then to bury the turntable at the top of Mt. Everest?..sorry for the exaggeration but you get the point)? Sorry if I've asked a very trivial question but I want to get this clarified.

If you guys can direct me to some other thread where i can get this doubt cleared, I'd like that too.

I hope I can clear this up for you, and give insight for others.

Ideally, a plinth will have certain properties which will help reduce the amplitude of vibrations in the turntable system. This is done by considering three parameters, viz. stiffness, mass and damping. Of fundamental importance is the fundamental resonance frequency of the plinth, for that defines the point at which the stiffness contributes nothing, but where the mass controls the attenuation of vibrations. Somewhere above (usually) this frequency is the critical frequency, above which damping is the controlling influence, and it is damping which is most important, as it controls the amplitudes of the vibrations, especially the resonances in the system.

So there are three frequency regions which the plinth is controlled by, the bass region, where stiffness has the biggest influence. This region is defined as that which falls below the fundamental resonance of the plinth. The next region is controlled by mass, which is defined as those frequencies between the fundamental resonance frequency and the critical frequency. Above critical frequency, damping is the controlling factor. However, the amplitude of ALL the resonance frequencies are controlled by the intrinsic damping factor of the materials used to make the plinth, either as single materials, or composites.

Now, the critical frequency depends, among other things, on the thickness of the materials making up the plinth. The thicker the material, the lower the critical frequency, the smaller the region where mass has control. Now you can see why nailing the plinth to Everest is a hopeless task, as the mass of Everest will have no effect whatsoever!! [goes for all mountains!].

The best plinths are low mass, thin panels of materials with high intrinsic damping. Such materials include some woods, especially ironbark and ironwood, but most woods are not up to the task, including plywood. Resinated woods, such as Panzerholz, Permali and even resinated bamboos are also very good. Other materials, including all natural stone, ceramics, most plastics and all metals are particularly poor in this respect. I am not surprised kuruvilajacob dislikes slate, it is far too stiff and massive, and has a very low damping factor. Just tap it with a hammer and listen to it ring!

Hope that helps.

 

[peace_sells]

Thanks cat's squirrel! That was a really nice and descriptive explanation. Thanks to the others too for clarifying this for me.

 

[reubensm]

Once I experimented with Slate plinth for Garrard 301 and it sounded dull and lifeless. I agree with G401fan that some plinths can be an 'overkill'. But for 301,401 or L 75 heavier multi-layered plinths should absorb vibration without much damage to reproduction. I always take such steps instinctively and only the slate plinth has been a disappointment for me so far

I plan to place your multi-layered plinth on a granite slab (the plan is for the granite slab to be mounted into the equipment rack)

 

[reubensm]

Hi Reubnsm
You will need a heavy plinth for your Lenco.

Regards
Sachin

yes Sachin, I figured that out. Any process with your Lenco project?

 

[sachu888]

yes Sachin, I figured that out. Any process with your Lenco project?

It is still playing beautiful on Pet containers. We have almost finished diy Schroeder tonearm, plinth should be ready in February.

Regards
Sachin

 

[cat's squirrel]

Hi Reubnsm
You will need a heavy plinth for your Lenco.

Regards
Sachin

or not.

There are two things (at least) which need attending to with Lenco 75's.

The first is to do with the dished pan, which holds the motor and main bearing. The steel plate it is made from is thin (~2mm) and prone to bending and vibrating. To mitigate against this, and keep the thing as standard as possible, the pan must be supported, especially around the bearing. Some people mount the pan straight onto a plinth, others use brackets of some design to do the same job.

The other problem is that the arm on a Lenco75 is mounted on a steel top plate, so that vibrations from the turntable mechanicals (and other external sources) are transmitted up the arm mount and into the arm/cartridge. So the top plate must have any vibrations reduced to a minimum.

Careful design and suitable choice of materials will provide this, guessing probably won't.

In the design of a plinth, the three parameters which are most important when choosing a suitable material or materials are stiffness, mass and damping. One may think that the higher the mass the better, but that is not the case. To increase mass, one can choose a denser material or increase the thickness of the material. However, denser materials are usually stiffer (there are exceptions, as always). And making the plinth thicker has its problems, to do with the critical frequency. As the thickness of a panel doubles, the critical frequency halves and the fundamental resonance frequency increases. As the region controlled by mass is between the fundamental resonance frequency and the critical frequency, one can appreciate that increasing the mass by increasing thickness will severely limit the region where the mass is supposed to have a beneficial effect. Get to the point where the critical frequency is lower than the fundamental resonant frequency, and no matter how much mass the plinth has, it will have no effect whatsoever (lets call it the Everest effect!).

It is possible, knowing many characteristics of a material, to determine the best thickness, and for most suitable materials, that lies between 10mm and 30mm, so not really a heavy plinth!

Germane to all of this is the choice of suitable materials, and the most important parameter is the material's damping factor. Think of it as representing the time taken for a vibration to die away (exponentially in the case of damping). The shorter the time taken, the better the damping (and the higher the damping factor). Good materials will have a damping factor of around 0.1 to 0.2, excellent ones 0.4 and above.