Why Use Aluminum for a TT Platter?


Mass I am told is a good thing when it comes to TT platters. Lloyd Walker for one extolls it's virtues and as a rule some of the better turntables like to brag about their big ..Platters. Why then would aluminum, known for it's light weight (low density) turn up as frequently as it does as a platter material. I know it is easily machined but isn't there anything better and much denser.
mechans

Showing 3 responses by t_bone

Chris/Teres,
My understanding of the technical term for cogging means either slots or
cores are required (though I could imagine where badly-designed slotless
coreless motors could have other iron present. I assume that the 'cogging'
issues you mention on slotless AND ironless motors comes from the fact
the stators are not infinitely small. Does it also come from coil material
saturation/resistance of some kind (i.e. Induction is not perfect because of
materials issues)? Is there something else I am missing?

I completely agree that in the end it comes down to execution.
If you use enough aluminum, it can get pretty heavy. It is a lot easier to work,
and a lot cheaper than using stainless steel, bronze, brass, copper, feric
alloys, etc. When you are trying to mass produce (and keep in mind, in the
70s, companies made turntables like today they make ipods), ease/speed of
creating the shiny metal piece was paramount for many.

Moving off-track...
There are DD tables with heavy platters. I have a couple with platters which
weigh 20+lbs.

Not all DD motors are built to instantaneously bring the platter to speed if
there is the slightest speed variation. Some are built to bring back to speed
more slowly.

Cogging is an artifact of certain motor types (generally, those with iron cores).
Not all motors cog. The top brushless, slotless, coreless motors by Pioneer,
Yamaha, Denon, and others are (generally) extremely smooth (zero cogging).
They'd be a bear to make again in some cases. In general, these motors will
have less torque than slotted motors like Technics.

From what I can tell, the first really heavy platter came on a belt drive Melco.
Micro copied soon afterwards. That said, DD platters gradually got heavier on
the high-torque motors. The Sony PS-X9 of 1976 has a decently heavy platter
which is very wide (more inertia). The Technics SP-10Mk2 platter is not light.
The Yamaha PX-1 of 1978 is also a decently heavy platter, and the higher-
end tables from Exclusive, Onkyo, Lo-D, and others from the early 80s mostly
had high-mass platters even though they were DD tables (they all had
coreless linear motors too). The lighter platters on high-end tables came on
Denon, JVC, and most other Sony tables, which operated with substantially
lower torque than other high-end tables.
Chris,
I was wondering what physical phenomenon generates the torque ripple in a slotless, coreless motor. Any thoughts?