Turntable speed accuracy

Dover, it has been sitting for some decades, I suspect.

The trust bearings are interesting. They are a set of polished platforms that reside beneath the platter. The drive shaft comes through the center and has nothing to do with them!

I almost bought the timeline. Glad I didn't. using a Fluke digital multimeter is a more accurate way to set your speed, rather than trying to look at a laser being somewhat stationary on a wall. Use a test record at 1000Hz and connecting the Fluke to the output of the phono stage. For 45 rpm, the same 1000 Hz tone should read 1.35k Hz. The Fluke cost about $125.00.

Rockitman,

I have been doing almost the same. Card as test LP 1khz tone through my Prism Orpheus into my MAC Mini. I see it on the screen. You can see the stability of the signal and all. And I can hear the differences as well.

Here are some of my own observations and hypothesis:

1) Regarding how important platter mass is for speed stability. IMHO you cannot assume a higher platter mass is better independent of drive mechanism. In other words, the platter mass and drive mechanism need to be considered together. Picture a 100 lb platter driven by a wimpy motor. The motor needs to be able to keep the heavy platter spinning at speed. Assuming it can do that, any deviation would be difficult to compensate as the inertia of the platter would work against the wimpy motor.

2) Seems to me, resonance issues aside, the energy of the drive mechanism is much more important. That is why I think high torque motors and flywheels driving platters makes sense. The more powerful the mechanism the easier it is to keep a light or heavy platter moving at speed. Therefore, a TT should be designed with drive mechanism energy and platter weight in mind.

3) My understanding is that AC motors run at constant speed by default, whereas DC motors do not control speed per se but torque. That’s why most DC motor driven TT’s slow down with stylus drag. However, most AC motors, having sufficient drive energy fair better. I suspect that DC motor driven TT’s with large flywheels (e.g. Micro-seiki HS-80 and the Forsell) sound better because the flywheel adds drive energy and compensates for the DC motor instability on its own. Seems to me that a TT with AC motor with high torque or added energy through a flywheel has some advantages to DC motor, with higher motor torque, but without s flywheel.

Just my two cents

Andrew

I would like to qualify my statment above:

"That’s why most DC motor driven TT’s slow down with stylus drag. "

I'm referring to DC-motor drives TT's with an open-loop control system. This means that the actual speed is not compared to the set-point and adjusted for mismatches.

I would also add that TT's using multiple motors closely spaced toghether (e.g., TW Black Knight)help increase the tourqe of the drive system.

Andrew