Turntable mass

jules · « **on:** 17 May 2006, 06:23 am »

Ok vinylophobes, I'm a sceptic but I'm also considering a TT upgrade so I'm open to your thoughts ...

Is there an optimal mass for a turntable?

Is there some elegant science/maths in the design of certain colossal TTs or is this trial and error?

If using a wooden platter contributes something to the end sound exactly why is it so?

Yes, I can see that a certain amount of mass is necessary to give the revolving turntable inertia to smooth any slight speed fluctuations. Yes, I can see that a certain amount of mass is useful to prevent vibrations of particular frequencies. On the other hand I've noticed that the wood in the tone arm of, for example a Teres turntable, appears to be the same material used in the platter and I would have thought that the tone arm wood, would have a far greater influence on the signal output than the mass of the turntable in that case [though I'm not specifically asking about Teres only here].

I'm not a fan of a purely physics /electronics approach to any part of audio but I reckon that if a design appears to go beyond what seems to add up there should at least be some sort of reasoning to call on.

jules

Scott F. · « **Reply #1 on:** 17 May 2006, 11:23 am »

Hi Jules,

Give these articles a read. Goeff over at TNT-Audio gives loads of good information on tonearm and turntable design in a series of arm and table reviews.

http://www.tnt-audio.com/sorgenti/sources.html

Scroll down to the Analogue Stuff section. The first six articles cover most of what you want to know but the following ten articles are peppered with some really good design concepts and explanations.

Hope that helped.

jules · « **Reply #2 on:** 17 May 2006, 11:29 pm »

thanks Scott ... I'll go and have a good browse

jules

TheChairGuy · « **Reply #3 on:** 18 May 2006, 02:44 am »

Hey Jules,

I've wondered along the same lines and for some time about TT's and mass.

All other things equal, more mass is better than less. But, there seems to be a lot of good 12kg (25 lb) plus machines out there that are good...but become exceptional with either a stand alone motor and/or some kind of speed regulation.

The 12 year old VPI HW-19 III I now own is pretty hefty at over 20kg (45 lbs or so), with a 4.5 kg (10 lb) platter and tight bearing tolerances and a good RB250 tonearm (with several upgrades) - yet it's seriously compromised by a very intrusive motor that leaves an energy trail all the way to the tip of the cartridge. Definitely, not good.

So, all that good, healthy mass is wasted...until I spend another US$400 for a stand alone motor assembly. It's not worthwhile to add anything else until I remove the shaky motor from the picture

jules · « **Reply #4 on:** 18 May 2006, 04:32 am »

The reason I'm asking these questions [and I haven't been able to find quite the answers I'm looking for] is that I'm compulsively DIY when it comes to anything involving wood. In this case I've got some very fine timber left over from an amp case I've built [and a pre-amp case I'm building] and I've been drawn into the idea that I could have a go at a turntable.

It seems that there are two approaches to the connection between vinyl and the platter that have parallels with speaker feet. One approach is to use a mat which I presume provides damping but could be found guilty of muffling the sound [am I on the right track?]. The other way to go is to have the vinyl in direct contact with the mass and thus "as one" with the harmonic qualities of the turntable.

Thinking about the vinyl-wood bond I first drew a parallel with the connection between the cylinder head and block of an auto engine. Now a cylinder head is a massive three dimesional lump which looks very rigid. For all of that, there's no way you could attach one of these things with a single bolt through the centre. What's actually called for is maybe a dozen fairly closely spaced bolts tightened down to significant torque figures.

The next thing I realized about an LP is that the centre and the edges are thicker than the tracks. To allow for this with a solid tt it's necessary to have a slight recess for the label part of the thing to sit down in so that the grooved section is in contact with the wood. The outer edge is going to have to hang over the edge for the same reason [I presume though I haven't seen one in action].

The weaknesses would seem to be ....

*Vinyl is virtually only two dimensional and has very little rigidity. Given that the only possible way to hold it down is a central clamp, this makes the bond very tenuous.

*If the clamp is slightly smaller than [or about the same size as] the label, which is in turn slightly smaller than the recess that accepts it, any force applied to the clamp has a tendancy to make the vinyl bowl shaped. [Maybe I'm wrong here but it looks to me that the size of the clamp has to be such that the head doesn't come in contact with it as record ends which forces the clamp to be of smaller diameter than the recess].

My conclusion is, and this is entirely experiential, that the bond between vinyl and wood is weak to the extent that there's not likely to be anything like "oneness" happening. All in all I'm not convince that huge amounts of mass produce the results they might appear to on face value.

jules

BobM · « **Reply #5 on:** 18 May 2006, 01:04 pm »

I like your analogies about the bond of the record to the platter surface. Yes, it's a mechanical connection that seats the mass of the platter to the somewhat fragile and flexible vinyl that the needle relies on for its information.

VPI used to tout their platter composition, saying it was very close to the composition of vinyl. But now they've gone to an acrylic platter like so many others. Huh? Aesthetics taking precidence these days, I presume (sexy sells).

VPI also still use a small rubber washer around the spindle. The clamp pushes the record down against this and facilitates a tighter bond with the platter by creating tension. Tapping your fingernail against the edge of the record will demonstrate whether the bond seems solid or if there is a bowed shape to the record after clamping (you'll hear the noise and know).

How well does this method affect the TOTAL surface of the record and its bond with the platter? Who knows, but it sounds reasonable and relatively simple and inexpensive, if not perfect.

Teres touts their wood platters, which look really great, but may have similar issues to anything else - it's not all one piece and the clamp is still needed.

Then ther are peripheral rings, which I presume is an engineer's kludge to a less than perfect solution. More effective, but a bit klutsy. A level of extra effort that only a vinylphile can love.

Vacuum hold down seems to be the best method, but it is difficult to implement, costly, and noisy.

Almost anything short of an epoxy has its faults. Pick your poison ...

Enjoy,
Bob

Russell Dawkins · « **Reply #6 on:** 18 May 2006, 05:07 pm »

I guess the very keenest (rich) vinyl-o-phile would buy two copies of every record and have a platter devoted to each record side, with the record permanently bonded to the platter. A little inconvenient, in that you'd have to change platters to change sides, but that interface could really be optimized!

In a more serious vein, on the surface of it (!) it would seem to make sense to make the platter small enough not to support the outer raised edge and to incorporate some variant or the VPI rubber washer with a concave underside to the clamp to produce a downward bowing of the record.

The experimentally inclined should find some way of listening to a record player with the needle in the groove and the platter not turning, but immersed in the sound field produced by the system playing music from a different source (CD, tuner, iPOD) to hear just how much of the ambient sound is picked up by and re-incorporated with the music coming off the record while the record is playing. Might be a much bigger factor than the various schemes for "draining vibrations to ground" assume. If this were the case, the biggest improvement of all would derive from creating a semi anechoic and sound-isolated environment for the turntable.

20+ years ago I was pondering bringing such a device to market as furniture to enclose the entire system and if I were "heavy into" vinyl and/or tubes I would be listening that way now. To the extent that microphonics are significant, it makes a lot more sense to me to eliminate the problem at the source rather than to try and make individual devices immune.

mgalusha · « **Reply #7 on:** 18 May 2006, 05:20 pm »

The Teres tables use a delrin washer between the platter (top of the bearing shaft actually) and the record. When the clamp is tightened its make the record very slightly convex. The area of the label is slightly recessed. It seems to work very well but like everything else I'm sure there are trade offs.

I know my platter weighs in at about 25lbs. It's made from solid cocobolo and filled with lead shot. No shortage of mass.

JoshK · « **Reply #8 on:** 18 May 2006, 06:14 pm »

Mike,
I forgot, where did you get your platter machined?

mgalusha · « **Reply #9 on:** 18 May 2006, 08:52 pm »

Josh,

A friend of mine has a machining business and was kind enough to do the work on the platter. I've since purchased some machine tools and trued the platter back up, it had shifted a little as the wood became drier.

If you need some custom machine work done I'd be happy to put you in contact with him. We've known each other for over 20 years and he won't screw you.

jules · « **Reply #10 on:** 18 May 2006, 10:34 pm »

Mike,

does that mean that with the Teres, you have clamped contact at the centre, and the slightly domed vinyl only makes its other contact at the outer edge?

jules