Turntable Material Discussion

[TubeHound]

Hi,

I am a returning member and plan to build a DIY turntable. I am an amateur builder, but consider myself a craftsman at heart. A link to my introduction post.

Returning member

As with all successful projects, planning is the first stage in a successful build.

I want to start a discussion about the materials used in TT designs and why that is either good or bad.

I have once owned a Musichall MMF-7. I hope to build something more like the Teres, in trying to achieve a high-end design.

As far as materials, I have considered Cast Acrylic Sheet, Wood and Aluminum for the platter and pretty much the same for the plinth. Deciding on which to use is still open.

What are some of properties of these materials, their advantages and disadvantages?

Staying opened minded, are there other materials not listed that should be on the list and why?

Regards,
Paul A.

[YNWOAN]

My own experience and experiments in the realm of Turntable design suggest to me that high mass is not necessarily a good thing. In addition, I do not believe that non suspended designs are free from the effects of acoustic feedback. I recently experimented (again) with the use of acrylic as a platter material. At first I though that it gave slightly sweeter high frequencies and a greater dynamic range. After extensive comparison I have now concluded that the 'sweet' highs are in fact rather one dimensional in character and the increased dynamic range is the result of a slightly bloated and opaque lower mid.

In my own design I favour a light but very rigid carbon fibre construction for the sub chassis. The arm and platter are attached to this structure. This is then coupled to a relatively high mass structure via an elastomer decoupling. This mass is further suspended at a low frequency 2 to 3Hz. This arrangement I believe to give the sonic benefits of a non-suspended structure whilst still maintaining the isolation properties of a properly suspended design.

I have, over the years, experimented with using a range of materials. Certainly material choice makes a sonic difference, as dos construction technique. However, the alteration of a specific material for another, whilst leaving construction unchanged, tends to have a tonal effect rather than one of truly increased resolution. Often these tonal variations can be very complex in nature and can give the effect of increased resolution though this is often at the cost of decreased resolution in another area. If one wants to genuinely increase transparency one must consider construction method and, even more importantly, the design of the deck itself. My own experience suggests that a significant quantity of experimentation is the only way to achieve really good results.

[Miniwatt]

Originally posted by YNWOAN
I favour a light but very rigid carbon fibre construction for the sub chassis.

This makes me curious.. What kind of carbon fibre material did you use? (bars, sheets) (I know nothing about that..)

Pics?

[jrevillug]

Interesting results there. May I ask what you put your TT on? Is it a typical suspended wood floor, a concrete floor, a wall mount or ____?

With the Elastomer coupling- is this over a large area (like a layer between carbon and the mass) or is it more like a suspension?

I can see that a non-suspended design will be affected by any vibrations. However, it is frequently the case (or so it seems to me) that high-mass TTs are suspended in a way- a suspended stand, or inner tubes between the stand and the TT. This seems very similar to your ideal design.

Also, what are your findings on increased Platter mass? I see you say that increased mass is not always good, but is that total mass or platter mass?

Would you consider a constrained-layer damped Platter a design change or a material change?

[marekst]

Hi Paul,
My experience in vinyl is a short one and I’ve only built one turntable but I figured out one thing: LP lies on a platter and the material the platter is made of is primarily responsible for the sound. For my platter I made a progressive density composite. I did write about the composite, but can’t comment on the sound yet as I am redesigning magnetic suspension of the platter (magnetic field near the inner groves is too strong).
DIY composite platter
The base of my TT is made of mixed materials: cocobolo wood with lead loaded aluminum ring lies on top of acrylic chassis. I have chosen heavy plinth to absorb bearing noise! YNWOAN has a totally opposite concept: lighter, cast metal platter on ultra light corrugated cardboard/carbon fiber composite plinth. The funny thing is, we bought are working on similarly screwed up magnetic suspension: I because my platter is too heavy for the bearing, he, because the bearing is too noisy for the platter plinth combination.
I have concrete floor and do not play too laud so I do not care much about suspension, feedback, etc. My TT sits on MDF (reinforced with fiberglass and oak) and that’s enough insulation for me. Two different freaks have different sound perception and agendas…

It’s another matter to make TT structurally strong for long term stability under the load of heavy platter. With your milling machines you can work with metals, so you have no problem there. I would look at aluminum chassis like Sota Millennia and combine it with some wood. Acrylic has a tendency to sag under load; wood alone will warp with time. I got my acrylic for free, so I used it to stabilize my wood plinth. Teres uses wood blocks saturated with epoxy – that kind of wood does not warp. I didn’t get a chance to listen to Teres or other high end tables but if you live near civilized world you should be able to audition Teres and compare it with acrylic or metal machine.
For more material and construction options you can study Morsiani’s side and read about new AudioMeca TT on TNT.
The tonearm is more important than TT so consider making one also.
Greetings from another amateur,
Marek

[sq225917]

Ynoan's bearing, platter and sub platter are all from a Sondek,so there aren't too noisy for the subdeck, in fact even without the mag-lev it's pretty damn quiet.

with it, it's deathly silent..

[YNWOAN]

Sorry, I've been a bit bust to reply before; but here goes:

Yesterday I changed the arm board on my deck for a carbon fibre composite one - still evaluating this.

Also, today, I altered the specific implementation of the magnetic main bearing my deck uses (very happy with this final incarnation).

If I may address a couple of the points made by 'marekst' first; I have experimented quite widely in the past with platter mats and a little with platter material. Whilst the material the record sits on can, and does, have a significant effect it is by no means the sole or primary arbiter of sound quality.

Also, I haven't got a clue where 'marekst' got the idea that my main bearing is noisy. As 'sq225917' states, the main bearing is from a Circused Linn LP12 and is in fact remarkably quiet. I believe a misunderstanding must have taken place as the statement that my main bearing is too noisy for the platter chassis combination I am using is completely inaccurate.

'jrevillug', my deck is in fact built into a floor stand. The lower part of the plinth is bolted to the stand and it is, in fact, an integral component. I have a suspended wooden floor in my listening room. It is possible to stamp on the floor close to the deck without exciting the speaker cones - even when the volume is turned up very high.

It is true that many owners of non-suspended mass loaded designs use an additional layer of isolation - Vibroplane or seismic sink etc. I feel this rather proves my point regarding the need for low frequency isolation.

The issue of increased platter mass is a complex one. On the one hand an increase in flywheel inertia is entirely beneficial. The more that motor fluctuation, or transmitted vibration, can be smoothed out, the better. On the other hand, platter mass is undesirable from the point of view of energy storage. The energy I am referring to is that generated by the stylus and fed into the system via the record surface and the tonearm (via the chassis). I propose that an external fly wheel be used to obtain the ideals of high energy storage (rotational) whilst being able to use a very low mass platter (this will be incorporated in my next design).

The elastomer suspension consists of three 'pods'. The chassis sits on these pods via adjustable points (for levelling). The higher mass section that all this sits on is further decoupled by springs at a much lower frequency. The motor is mounted separately.

I did take a few pics today - will try to post them soon if people are interested.

[marekst]

Ynwoan,
In “Magnetic turntable bearing - Post #1” you wrote:”Friction levels are substantially reduced and background noise is hugely reduced”. I wrongly assumed that you were talking about bearing friction and background noise generated by bearing friction. I also wrongly assumed that before that huge reduction, whatever you hugely reduced, was pretty damn huge. My bad, sorry!
Marek

[YNWOAN]

Hi 'marekst', and thank you for the quick response. On reading your last post I now understand the confusion; and I am entirely to blame. Essentially, the misunderstanding is because I rather over stated the level of improvement. Friction levels are reduced but when I said 'substantially' I should perhaps have said 'slightly'. The main bearing shaft is approximately 10mm ground and polished stainless steel. This runs in a close fitting synthetic journal. Most of the friction is from the sides of the bearing. No free play is evident.

However, bearing noise is significantly reduced. The previous bearing setup with a radiused and polished tip resting on a hardened and polished plate was subjectively silent. No noise was subjectively apparent. However, the addition of the magnetic bearing showed how much noise the previous thrust plate arrangement must have been producing. Between track silences are now genuinely silent - a quite unnerving quality at times. It is difficult to fully appreciate this quality until it is heard. If a record was mastered on tape it is very easy to hear the very start of a track as you can clearly hear the tape hiss at the beginning - before the music starts and sometimes you can hear the tape hiss alter during the track as editing takes place.

I am not referring to trying to make a poor bearing into a good one – I am more interested in absolute levels of improvement. The problem with noise being generated at the point of contact is one I believe to be present in all good quality bearings of this type (virtually all turntable bearings on high-end turntables).

[jrevillug]

Thanks for that. I can see how well your suspension setup works. Do you find much difference if you try the bearing directly attached to the heavy suspended mass? Or have you not tried it? It seems to me that these will sink unwanted HF energy from the bearing and arm.

I do agree that there needs to be some isolation somewhere for any TT.

The issue of stored energy in the platter causing time-smearing of the sound is very true. Would it be possible to dissipate that within the platter?

With the flywheel design, you will have to be very careful about the coupling between the platter and fly. If there is elasticity there, as in a belt, you will find that the speed varies, especially if the inertia of the fly and the belt end up with a resonant freq. within the audio range. This is the reason the I personally perfer the idea (remember that I am just doing thought experiments at this stage) of a big, heavy, well-damped platter.

I would be very interested in photos.

James