Is a Garrard 401 or 301 "accurate"??

@noromance I have been fortunate to share in a variety of demonstrations from Idler Drives, I have also heard Thorens Models and the Garrard 301, but these are too long ago in the past to make a recollection of.

In the earlier post, I should have added a Corian (owned) and Polybentonite Resin Plinth, to the list of Plinths I have been demonstrated in use on a Idler Drive.

There is at present, a move toward Densified Wood in certain communities, where the board is to be used as a Plinth Material for Idler Drives and the users of Plinths produced from Board such as the Brand Panzerholz or Permali are making very positive reports.

I own boards in both Densified Wood Brands but have these materials at present reserved for another Model of TT and Plinth Design. 

My most recent experience of being demonstrated a Idler Drive is a Garrard 401 that has been mounted in a Plinth with a Top Plate produced from a Side and Top Pressure Compressed Bamboo Board.  When Bamboo is produced using this method, the Damping Factor is 0.200.

The Damping Factor of Permali is 0.688, Panzerholz is 0.599 and Polybentonite Resin is 0.618, the resin is a common 'go to' material for a Idler Drive, it is Massey and as far as I know, it does not dissipate energy as efficiently as a Densified Wood or the lesser efficient Compressed Bamboo.   

The Bamboo Top Plate Mounted 401 > Origin Live ' Illustrious ' Tonearm > Sumiko Pearwood Cart'  has had Isoacoustic Footers and has been mounted on a Sub Plinth assembly produced from my owned Panzerholz Board and AT-666 Footers.   

The demonstration proved to be quite attractive and memorable, the 401 had recently replaced a SME 20/12 > SME V, the group in attendance and the 401 owner were not missing the sold of SME equipment that were all quite familiar with.

Through a friend I have listened to various works undertaken on a standard Lenco GL 75 Bearing and their methods adopted to rigidly secure the Bearing Housing from flexion.

I have had my own PTP Solid Nine used a comparison to the friends undertaken works, with the outcome being assessed that  a standard Lenco with selected methods adopted, can sound almost identical to a PTP, possibly only the Plinth Materials > Tonearm > Cart in use being the main influences on the differences detected.

Shortly before the Covid Lockdowns, I would have suggested it is impossible from  my experiences to pick an absolute preferred TT, as their were too many variables in the demonstrations, i.e, Plinth Materials, Tonearm, Cart's and TT Mounting Methods.

This changed just prior to the Lock Down Period, the friend with the GL75's had received a Extended Length SPH Bearing, it was supplied as a Special Version, as my friend had encouraged the Bearing producer to have a Spindle made that was a Composite design, the Spindle has Metal within the housing and a Ebony Wood is the attached Part of the Spindle that is visible above the Bearing Housing.

I also know the Thrust Pad was changed and the Lubrication in use was said to be working as Hydrodynamic. Being very familiar with this persons work and different concepts, as well as having my own PTP with the PTP bearing used as a comparison to their earlier work undertaken, I was not expecting too much of a margin of change.

The version of SPH Bearing in use attached to a GL75 with a Speed Controller, was the most indelible memory I have from any experience in recent years, it was a very gathered and exact presentation, that was the most attractive of many recollections and was being perceived as being noticeably improved over prior experiences.

@pindac Thanks for an enjoyable read. I have three refurbished 401s—two early and one later model units. One in 50mm Pennsylvania slate, one in 5x13 layer Baltic birch ply with a solid walnut top, and the other as a working skeletal project. I too have been impressed by the large improvement in sound quality when using the SPH bearing. 

The SPH Bearing is a success for two reasons, one being simple Geometry, when the extended length option is chosen the spindle will be less off axis when it rotates due the extended Spindle Length.

The other reason is that the common designed Vertical Plain Thrust Bearing from a vintage era, does not have Hydrodynamic lubrication as part of the design, a Sintered Bronze Bush is usually the part selected as the Sacrificial Material within the bearing housing. I have not seen evidence that a Sintered Bronze Bush is able to release a impregnated lubrication at the heat a Spindle Rotation can produce, and the Bearing Housing is unlikely to have a design that has a Hydrodynamic Lubrication.

The outcome is that an original design for a vintage bearing will end up with Metal to Metal contact between the Bushing and Spindle, and the Steel Ball and Spindle Base will most likely be in contact with each other as well.

This will mean noise is produced and it will be quite easily detected with a Stethoscope, which I have been shown on a few occasions where various stages of bearing work is being carried out.

SPH is using Thermoplastic Bushes and Thrust Pads, with a Non Metal Ball, so there is no Metal to Metal contact, this is a great improvement and the Stethoscope will show the quieter condition, by creating a Hydrodynamic Lubrication, the overall environment within the Bearing Housing is further improved.

A Vintage Bearing Assembly with Metal Parts that are without excessive wear to the used parts and a Modern design where non metal parts are selected in place of the Metal, if both set up to have Hydrodynamic Lubrication should both be as quiet as each other, as the Oil is supporting the Parts and separating the parts from coming into contact.

This leaves three other factors at play for the impression the SPH Bearing has made, the Geometry due to the extended Spindle Length, the Composite Spindle removing a Metal to Metal contact between Platter and Spindle, and the other being the use of a non Thermoplastic Thrust Pad, which will have removed the material that has elasticity and be subjected to the effects of Vertical Compliance.

The question is as a subjective analysis, can these three factors really be the influences that made the use of the SPH Bearing stand out as improved over the other versions.

I have a bespoke produced Tonearm, that is a modern thought process applied to a Vintage Model, that has been rebuilt in the concealed areas with Modern materials used for the design and a very careful approach to the R&D carried out to select the machining tolerances for the new materials.

I have followed this Tonearm as it has evolved in stages of design, and have been invited to receive demonstrations of the work as it has evolved. I know of one occasion when a material with an improved property, was used in place of an earlier selected material, the Tonearm moved forward in a night and day noticeable improvement, so the method used for the assembly within the Bearing Housing ’could’ be a feasible explanation.

Can you define "damping factor" as it applies to materials of which you might construct a plinth?  I can't imagine there is any single value that would describe that quality except if it has specific reference to a single frequency or set of frequencies, and perhaps other elements of the definition as well.

I use a source of information that has been a reference point within the HiFi community for many years, it is used both by Professional and Amateurs to extract information.

I have used the resourcefulness of the producer of the information further and they have received materials I am using and New to them for testing.

I have made it one of my goals to become quite familiar with materials used for Plinths that are described as having optimum damping, and the result is that I have become very impressed, and have moved away from the Massey Plinth Designs as the mounting methods.

I am keen to maintain the experiences had from being demonstrated the materials with a obove optimum damping measurement, hence my having access to Densified Wood and acquiring a supply of Permali and Panzerholz which carries a considerable expense.

The Polybentonite Resin is in my view a Massey Plinth Design, when produced it has very high measurements compared to other Massey Materials, the Resin measures above optimal damping, but the sonic is different from Densified Wood.

To put a further perspective on the above Materials that are with High Intrinsic Damping, when compared to other regularly mentioned materials such as Slate 0.017 and Aluminium 0.004 it can be seen the divide in the measurements are quite vast and the stone and metal fall way short of optimum damping.

The following is the words of the technician who produces the testing and recording of a wide variety of materials:

When a sample of material is struck, it vibrates, the frequencies at which it vibrates is dependent on its dimensions, its stiffness (Young's modulus), density and how much it deforms when compressed (Poisson ratio).

How long it vibrates for is a function of its damping factor. Have a look at the trace below. My three axis accelerometer was taped to this material, and struck. The sound was captured on a computer, and recorded using Audacity software. You will notice the rate of decay is quite well defined, fast at first, and becoming asymptotic towards the end. The damping factor is calculated by looking at successive peaks, and measuring their heights from the zero line. This gives the 'log decrement', and from this the damping factor is calculated.

The damping factor, Greek letter eta, n , is a dimensionless number which represents the amount of intrinsic damping a material has. The property is like density, it is irrespective of other properties, including dimensions.

A material with a damping factor of 0.07, or above, is said to be damping, above 0.1 and it is a good damping material, and as the damping factor is twice the ratio of its damping compared to critical damping, a value of 2 represents critical damping. Most materials encountered in hifi products have a damping factor between 0.01 (or below) and about 0.2, so they are well below the critical damping figure.

The trace below shows how a slate tile rings for about a second, when struck, (and they say it makes a good plinth material). Its damping factor is 0.017, very poor!  Amplitude up the y axis, time (seconds) on the x axis.