Turntable speed accuracy

Palasr wrote: "While frequency accuracy (and adjustablity) is one issue, it doesn't begin to address waveform shape, harmonic distortion, phase amplitude and shift, and all the other interesting things that go into generating a waveform suitable for driving a synchronous AC motor."

I have a Mark Kelly AC-1 drive controller on my VPI TNT that features separate manipulation of several of these parameters, while deriving an AC waveform from a 12V battery independent of the power grid. Unlike a VPI SDS, the AC-1 is a true two-phase controller-- it eliminates the phasing capacitor from the motor tower. Varying the separate effects independent of frequency is easily audible, as are differences between belts of varying compliance-- yet the strobe disk doesn't move a whit.

No one seems to set the speed as I do. I adjust speed while playing same known track on CD as well as TT. I measure with stopwatch and play simultaneously going back and forth such that the song start and ends at exactly the same time on both CD and TT. I change source back and forth, each note sounding exactly same that you can hardly tell diff. It helps that my main CD source and TT are set pretty much to same tonal balance. It takes few iterations, but then I listen without worrying about speed. Makes sense?

Don, I think you underestimate the situation.

"Speed variation "is" noticeable on classical piano "IF" you have played a piano, but typically the audience could care less. "

I cannot play piano, or any other instrument, or read music. I'm certain I do not possess perfect pitch. But when I listen to piano recordings I am quickly aware if the sound becomes either sour or cartoonish. That tells me something slowed down or sped up. It could be my turntable, it could be the power line, it could be someplace in the recording chain. But it is not difficult to hear when a recording does not sound like a live instrument. (And yes I understand there are multiple other factors in the "sounds live" experience.)

What is the best way to verify results?

It depends on what results you're trying to verify.

With regard to general speed accuracy, a good strobe like the KAB or the Timeline both work well.

With regard to stylus drag or other very short-term transient events, my ears are far more sensitive than such tools, which lack a sampling rate capable of measuring variations which occur over mere nano-seconds. YMMV.

What is the most speed-accurate drive method?

A car on cruise control, which will transport you to the venue of your choice to hear real music. All TT drive methods are compromised, each in its own ways, so there's no answer to this overly simplified question.

And is speed accuracy really the most important consideration for proper turntable design or are there some compromises with certain drive types that make others still viable?

Whaaat? That's like asking if a red car is best or should we shovel snow or plow it. ;)

1. Is speed accuracy really the most important consideration for proper TT design?

It depends on the sensibilities of the listener. Some posters on this thread and very many TT designers seem oblivious to speed variations that drive me up the wall. I in turn am only just able to hear speed variations that drive my partner out of the room, screaming. OTOH, neither of us has absolute pitch to the extent necessary to identify a TT that's running 1% fast or slow but effectively resists stylus drag, yet my mother's absolute pitch can. What's important depends on who's listening.

2. Are there some compromises with certain drive types that make others still viable?

There are compromises with all drive types. Which ones are viable depends on the effects they have and how audible those effects are to you. Nothing about one design makes any other design more or less viable. Independent phenomena must be judged on their own merits.

Thanks Doug. I have heard three turntables with you and your partner and none drove Paul out of the room screaming. I guess that means the two Teres turntables and the VPI Aries we all listened to together had absolutely no speed variations. I believe two were tape drive and one was a belt drive.

A red car is more likely to be seen in a snow storm than is a white car, and if either has four wheel drive, it is less likely to get stuck.