Turntable speed accuracy

I agree with Atmasphere. Turntables with excellent soundstaging (and resolution of fine detail, dynamics and bass detail)are signtaures of TT's with excellent speed control.

In my experience, belt drive TT's with AC moters with ample torque and low friction fair better than DC motor driven TT's all else being equal. I think one way to improve a DC motor driven TT is to increase the mass of the platter with good torque. I suspect that is one reason the Micro Seiki's do well and why the addition of acrylic platters on top of the gunmetal sound better.

Andrew

Halcro,

In my statement about AC belt driven TT's vs DC motor driven TT, I was meaning belt driven DC TT's, not a DC driven DD.

I have no experience with DD's yet. If I get a timeline will try to post some results.

Atmasphere,

Which Empire TT are you referring to? AC or DC drive ,belt type?

Empire TT's based on AC motors using belts.

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