Speed Stability

The rim drive may have speed problems if not set up correctly...there are fixes for all of it. Check the screw tension on the motor pulley(s). Talc or replace the belt(s)

Hi had the same problem, but on my NAD 533 TT. I initially though it was the belt. It however turned out that the motor spindle/pulley, on which the belt rests, had got spoilt (the brushes inside the spindle became defective). The belt was therefore slipping, causing a variation in speed and therefore the pitch.

I don't know if the VPI has a similar system (of a belt being driven by a spindle which in turn drives the platter) as the NAD

Frogman, You wrote, "No, the speed stability of turntables (even the best), does not equal that of digital sources playing digital recordings." What turntables have you actually auditioned for this property that you would characterize as "the best"? I don't mean to be provocative, but all of us occasionally make hyperbolic statements. Also, when you speak here of "speed stability" are you referring to accuracy (i.e., fidelity to the 33.33 rpm standard) or to constancy (i.e., ability to maintain the exact same speed over short time intervals while listening to music as judged by pitch constancy)? I think you would find that the best direct-drive and idler-drive turntables do very well on both counts, so well that you would no longer even think of the digital analogy. I think the finest belt-drive tables aided by a good motor controller would also cause you to re-think your statement, but I myself have not heard any of those for any length of time in my own system.

Lewm, I knew fully well that my comment would raise some eyebrows; I stand by them.

Having said that, I will gladly answer your questions. I am speaking about, as you put it, "constancy", not accuracy. I think the term "stability" is self-explanatory. I have listened to many tables over the thirty five years or so that I have been buying records. Those that I have fairly extensive experience with (althought not in my system, with the exception of the Linn), that I think could reasonably be included in the category of "the best" include: Goldmund Reference and Studio, Rockport Sirius, fully tweaked-out Linn, Technics SP10 MK2, SME, and Forsell. For the record, my favorite of those were the Goldmund Studio, and the Forsell. Of course, the other equipment in use at the time played a major role in the end result. I am tempted to include my own TNT6/ET2 set-up in that group, but although it is very good, I am not convinced, yet, that I can live with it for the long term.

I have already explained that I am very sensitive to speed stability. Perhaps the fact that I play music for a living has something to do with it. And I can tell you that in my experience, all the turntables that I have ever heard demonstrate some degree of speed instability, as compared to the sound of live music. Digital, to my ears, does not. It generally has a rock solid speed stability that is reminescent of the real thing. Now, we can talk about digital sound's failing in that it can sound too tight, and tense, compared to the real thing; but that's another story. I have always felt that part of analog's appeal is that it tends to sound more relaxed; even when it has good "PRAT". I believe that part of the relaxed feeling that it imparts is a result of the imperfect reproduction of rhythm.

I made it clear that I believe that turntables can sound excellent; obviously. But in the area of speed stability, although some can be very very good, there is still some deviation from the truth. In every other sound parameter, mainly as concerns timbre and dimensionality, analog is king, in my experience. Music's most important component is rhythm. Speed stability affects the reproduction of rhythm. To me, it is entirely within reason that changes in "constancy" on the order of hundreds of one percent, are audible. Hyperbole? Maybe. But I trust my ears, and this is what they tell me.

I'll support Frogman's general assertion, both from theory and from my own listening experiences and Paul's.

All turntables exhibit speed instability. There are no exceptions, only differences in degree and kind. When a mechanical drive system is confronted with a variable load (ie, stylus drag) at an unpredictable mix of frequencies, rise times and amplitudes, instabilities in platter speed are inevitable. The instabilities can be mitigated by good engineering of many kinds, but they cannot be eliminated. We can use Newton, we can't repeal him.

Can any particular listener hear the speed instabilities of any particular table? Who knows? FWIW, like Frogman, Paul and I have heard few TT's that don't shout certain speed instabilities to our ears.

We aren't musicians, but the music we enjoy is pitch accurate and rhythmically precise, so very revealing of speed instabilities. DSOTM won't tell you much unless the table really sucks. If you want to diagnose a table's speed stability, listen to Mozart or Bach on authentic style instruments, as in the recordings by Hogwood or Harnoncourt for example. Held notes and complex passages in music and recordings of great clarity will reveal TT weaknesses that are masked in heavily amplified and mixed music.

At RMAF 2008 Paul correctly identified 10-15 rubber belt drives without knowing anything about the tables, without even seeing them, just from the sound as we walked in the door. On 2-3 occasions he and I actually said "rubber belt" BEFORE we walked in the door, the time smearing was that obvious.

We brought just one LP to RMAF, an original instruments rendition of certain Vivaldi concerti. I chose it specifically because it reveals two things: speed instabilities of a subtle kind and fundamental/harmonic imbalances. I wanted to hear how Mosin's Saskia table handled subtle speed challenges (I knew it would handle the big ones). Paul wanted to hear if a certain cartridge would mis-handle fundamental/harmonic structures in the way he had predicted (he gets that way!).

We only bothered to play that LP in three rooms, Mosin's, Highwater Sound #2 and the room with that cartridge of interest to Paul. The Saskia handled this LP exceptionally well. The TW Acustic Raven 3 in Highwater #2 was also very listenable. (OTOH, the cartridge mis-performed exactly as Paul had predicted, though worse than even he expected.) We didn't bother to play this LP in other rooms, since we were there to enjoy ourselves. ;-)

FWIW, digital also has speed stability challenges, which we refer to as "jitter". Jitter doesn't sound like the speed instabilities from a TT or tape deck and we don't hear them as time domain issues. They are, but on a shorter time scale and with non-analog consequences.