Upgrade from TW Acustic Raven AC-3 to what?

Aoliviero,

You said...

"I have been pondering the technical aspects behind TT speed stability in a qualitative way. I think there might be situations where mass plays an important role. I tend to think about this as AC vs DC, low vs high torque, low vs high platter Inertia (driven by mass). I tend to bracket in the following fashion:

1) Optimum

a) low torque, high platter inertia, AC
b) low torque, high platter inertia, DC

2) Moderately optimum
a) high torque, high platter inertia, AC
b) high torque, high platter inertia, DC

3) Not so optimum

c) high torque, low platter inertia, AC
d) high torque, low platter inertia, DC
e) low torque, low platter inertia, AC
f) low torque, low platter inertia, DC..."

I agree, but believe the absolute details of it are somewhat determined by the drive implementation and other factors that may be specific to a particular design.

Win
Saskia Turntables

Dear Lewm, well - as I mentioned before - there are many audiophiles and "audio scientists" out there who do favor direct drive or idler drive in turntables ( both principles do build on the idea of "control" and the motor and its quality has a huge impact on the result) and who will present wonderful technical descriptions and "proofs" for their preference.
But that is not my problem. I do use thread/string drive with very low grip and "wanted slippage" to accomplish what I want and use extreme high mass and inertia to get to a kind of self-stabilizing system. This has one huge drawback: - a fairly long time to get to the needed speed.
I am using a motor which is extremely expensive (and weights 12 lbs without any cover ... raw) and would by the way qualify easily for the most demanding ID or DD TTs.
I have told you in a direct email what are the points behind direct drive and idler wheel drive and their origins and original purpose.
We will see all 3 drive principles in various versions side by side for the next decades. Every one of them will have their cheerleaders and followers.
Fine.
No worries Lewm - I certainly will not get nervous about anyone's experiments. I have done my own. Too many people do misinterpret their dreams, philosophy or ideas for physical facts. And any experiments result is depending on its conductors ability (or his will...) to read it and draw the (sometimes unpleasant...) objective conclusions.

Dear Aoliviero, the Studer capstans I worked and work with are all AC. In this model it is all about constant speed of the motor spindle/pulley/flywheel.
I see your point. A motor trying to compensate slippage by altering speed is of course a contradiction for the slippage concept.
In general - this concept is kind of tricky to set up and works only with certain TT's (platter mass...). It works with thread/string NOT with belt. It works best (as all drive principle in TTs) when the horizontal plane of the bearing is force free. The actual "embracement" of the thread around the platters diameter must have a pretty large angle - 210 degrees and more.
It not easy to fine tune, but once done it works smooth and reliable and gives extreme constant speed with ease. What I always liked particular about this model was the "natural touch" - letting inertia doing its work undisturbed.
Nice. Quite the opposite of the "control" approach.

The recent threads suggest that maybe the way to segment this better might be in the following camps:

1) Strong coupling to platter and strong control of plater speed

The direct drives would fall into this camp. As would most belt drives that have strong connection to the platter.

I would think that either low or high mass platters can fall into this category with high mass being better.

Either low or high torque with higher torque being better when trying to control a high mass platter with belt.

Either DC or AC with speed stability playing the more important parameter independent of motor type.

I would also think platters with purpisely hgiher friction bearings or eddy-brakes would have to fall into this category.

2) Loose-coupling to platter, use of platter inertia to maintain stability

This would need to be a string-based drive with enough slippage. Obviosuly, direct drives would not be present since there is direct motor coupling to platter.

I would think you would need to use an AC motor or the like since it is a constant speed device and would not change spindel speed if there is slippage.

I'm not sure if torque would matter for an AC motor.

I think one would defintely need the high platter mass in this case to maximize platter inertia.

I would think that a more freely spinning, "friction-less" platter would be better than something that is helb back by a large bearing friction or eddy-brake. But then maybe a certain amount would be okay?

Anyway, would seem that the number of turntables in camp two is smaller. Forsell? Acoustic Signature? Platine? Custom units?

Andrew

Yes, the "camp two" is considerably smaller. You may add to that short list the big Micro Seikis, Final Audio, Epic and Melcos of decades past. Than the german Apolyt from the 90ies with so far 15 units built and featuring the most extreme and most expensive approach of this principle. The classic Platine Verdier however does feature eddy-current brake (side effect of its vertical magnetic supported bearing) and is used today by various owners with all kinds of DIY-drives (I have seen idler-wheel driving PVs as well as tape, belt, thread and even transmission belts).
Cheers,
D.