Basis, Galibier are two that I've noticed having a bearing with more drag than one might otherwise expect. I expect there are others but these I have first hand experience with. If you spin these bearings with no platter they don't turn very many times. Add the platter and they spin a few more times before stopping. I would also think in the case of these two bearings that it is the tight tolerances and oil viscosity that provide this resistance.
I think of this as being a bit different than eddy current breaking, but it is hard to consider the bearing a table uses without also considering how the platter is driven. (BTW, in addition to Mosin, I understand Teres is using eddy current breaking in their DD tables and maybe in the Verus drive. But I'm not sure about the Verus.) As one can imagine, motors with differing degrees of torque may work better with a bearing with a bit more or less drag. It gets even more interesting when different belt materials are added to the system.
In contrast I recall stories about Walker tables and how they will spin a long, long time on that magnetic field bearing. I don't know what Walker uses for a motor, but I would expect that it is a very low torque motor.
The point I'm trying to make is that you have to take the drive system on any table as a whole. There are many designs possible to get to a solution. |
Free spin equals loss of control, in my opinion.
That's the best way to sum it up! Dodgealum, there is no noise issue. Because a bearing is designed with some drag does not mean that it is being created by allowing things to rub together. For the 'table designer this is much like matching a load with an amp. The motor will be able to control things much better if it is doing work against the load. This is what the bearing drag is for. |
Dertonarm,
the only table? Really? Perhaps you should try to listen to more 'tables. ;-) |
Ok, Dertonarm. I'm just wondering what you meant when you posted this. The only turntable so far which did it right (i.e. - correct application of "friction" to stabilize movement AND to provide additional damping to the platter) is/was the old venerable Platine Verdier in its original form (pre-1992) of bearing (without the ball support). Nobody else has gotten it right? |
Thanks for qualifying your position, Dertonarm. I understand now that you are referring to a specific approach taken by Verdier. That approach as you have outlined it does seem to be unique, but costly and hard to control from a manufacturer's point of view. As you documented there were other issues with this approach, so perhaps it wasn't all that to begin with. Seemed to be a good idea.
The eddy current breaking is a solid, proven approach. The problem is that it still seems to be beyond the financial means of most of us, so we are left with belts or idlers. To Chris's point, the non-compliant mylar belts and lower torque motors do sound very good. This type of belt along with a decent control mechanism can provide speed stability that is better than most belt drives and I believe it is very close to your average idler. I suspect this is because we are starting with a no-cog DC motor and the mylar provides a much tighter coupling to the platter than any stretchy belt. But that is going off on a different topic.
If nothing else this discussion should show that the designer must take the entire drive chain into consideration, regardless of whether the bearing or motor is chosen first. They still have to work together to produce a speed stable platform. |
Hey Dertonarm! Show us how it should be done right. Let's have a spec review. |
Absolutely. Start another thread on TT spec review, or something like that and let's see where the discussion goes. |
Lewm, "distance from the stylus"? Why would there be component that varied with this distance? Unless we're jumping to AS? |
Ah, yes!
a = (2*f*sin(x))/mass
Thanks for the trig review. ;-) |
I think one can some up the problems very simply, but I'm probably just restating what has already been posted here. As I see it the problem is not of design and proper application of physics. The real, true problem is integration. This is true of any complex system, not just with turntables.
You can design and plot and plan all you want. There will still be some compromise or component that you have to go to the shelf for. And then you are constrained by the operation of that component. That is when "feel" takes over, right or wrong. This is true for any complex system in the real world. This is the realm of practical experience and personal preference. This is also the realm of great breakthroughs and great failures. |
Ah, so now we are cutting to the chase.
In the real world, there are always compromises. Even the equations that we use to model real world behavior have compromises built in. One can certainly chose which to address, but on cannot avoid accepting compromise in one way or another. Even if one is not aware of the compromise(s) at the time. That is the leap from paper to reality. EVERY system, mechanical or biological or whatever, in the universe has built in compromises. It is unavoidable. So I propose that we drop the pretense that any system can built without compromises.
I agree that all turntable designers/manufacturers will make decisions based on commercial interests. Absolutely. They want to be able to sell what they have made. However, even those who profess to have spared no expense and made no compromises are deluding themselves, IMO. Look closer, I say to them. Compromises are there. |
Dertonarm,
The complex system I have been referring to IS the turntable. I don't believe you are really this thick-headed. I believe you are just looking for a flame war. Try AudioAsylum, they love that stuff over there.
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However - once again and for all - it is NOT nessecary in turntable design. Sorry to use a caloquialism, but I say bullshit! :-) Since we are on to the drive system in this thread let's use that. For the table that you designed. Did you not find that proper tension on the pulley was critical? Did your math/physics models predict that? How did you find, repeatably, what the correct tension should be? Let's look at the motor. DC or AC? How about the controller? If you open the doors I bet we can find your compromises. I'm not trying to pick you apart, just your position that no compromise should ever have to be made when building a turntable. The human experience over the last century with building LP playback machines shows otherwise. Now we can always argue over the compromises that ARE made. That is the sole reason for forums like this. |
Maybe we have a language barrier. I AM talking strictly facts. It is a technical fact that in order to integrate ANY system, compromises must be made. Insist all you want. You did make compromises throughout the process of designing your table. You have documented them here.
As I suspected, this discussion is moving into the realm of dogma. |
