Direct drive/rim drive/idler drive vs. belt drive?

Dan

For the kit designs I had two overriding criteria: they had to be as cheap as possible whilst still providing acceptable performance and they had to be almost universally applicable (hence your comment about platters / bearings). Unfortunately this means that they are a long way from optimised for any specific application.

For the bespoke designs I gather as much information as possible, to the extent of getting specific numbers for the rotational moments of inertia of the motors used from the motor manufacturers or in the case of one drive having to measure the numbers myself. I then build a model in a Spice program using some translational analogies and spend a lot of hours doing dynamic modelling.

Depending on the sophistication of the drive, the specific platter and bearing numbers can have some influence on dynamic performance but the most important parameters are the motor and its electrical control. When I am happy that I understand what's going on, we go to prototype.

The results? Well, I think you'll be surprised at what can be achieved with standard AC motors and belts even less compliant than your Mylar when the drive mechanics are understood. Similarly if a manufacturer sends me several samples of a high cost three phase motor and says "do your best then bill me" the results can be pretty good.

The downside is that the controllers end up being quite expensive. I don't know if there's a viable model for producing an aftermarket controller using any of these techniques.

Mark Kelly

Axelwahl says, "One expert put two Micro-Seiki on top of each other --- and then waits 5 minutes for the darn thing to stabilize the speed."

I think the flagship Nottingham Deco took such approach, with a massive 64 pound that is as thick as a microwave and driven by an extremely low torque motor that you have to finger spin it to start. Definitely doesn't seem very user friendly to me. I had a Spacedeck in the house at one point, very quiet table but the sonic was so mellow that it put me to sleep.

I use direct-drive turntables. Sometimes I use them to (VHS)tape-drive a "passive platter". So the motor is any one of my dozen direct-drive turntables. I no longer see these DD tables as record players, they are motors with a 12" pulley, "active platter", along with a controller. The combination of two platters takes up a lot of table space for sure. But they sound good. The only time when I can't hear any improvement from this tape-drive approach is when I use a dd table with a coreless motor. The coreless motor DD table sound just as smooth as the tape-drive set up. I have yet to try it with my Technics SP10mk2 table. It will be fun. I don't have any Denon turntables right now but I would like to try them as they are the only company I know who use an AC motor for their DD turntables.

I have to jump in here, perhaps a little late, but I have definitely enjoyed the banter. Especially the literary references; and I thought I was the only one who kept an unabridged Websters first edition at my reach. And what does my wife mean when she walks in the room and says "if you spent a third of the time you spend on this stereo stuff on our rlationship things would be better". This reminds me of a line from a poem I like "If you can keep your head when all about you are losing thiers and blaming it on you"
Back to the topic:
Question #1- Is the torque(twisting force)acheived by the platter dependent solely(sp) on it's driving force, or does it at some point become a product of it's rotating mass?
#2 If the bearing matches the mass of the platter, no matter how great (e.g. the fan blade on a jet engine), are the problems brought up about bearings solved?
#3 I believe the Feikert Twin TT uses a kevlar belt. Not much stretch there. If the belt is for all practical puposes stretchless, does it become a direct drive?

Thank you all for your responses, I appreciate the time you put in this, even if my wife doesn't.

Matt

HI Matt,

I can't help with the technical questions. I will offer this. My wife and I decided to stop "working" on our relationship after the first three years. That's when my first son came along. After that we just "worked" on making it through the day. It will be 34 years this winter. :-)

Mark,

I think you'll be surprised at what can be achieved with standard AC motors and belts even less compliant than your Mylar when the drive mechanics are understood.

If it isn't giving anything away, how is the filtering by the belt done differently with less compliance in the AC approach? Or am I confused by my own assumptions?