Direct Drive

@terry9

Thanks for your thoughts.

I've been thinking about tone arms with azimuth adjustment as I believe the stylus' axis needs to be perpendicular to the record even if it means the head shell is not at all parallel to the record.

My own tonearm adjusts azimuth to less than 1 minute of arc, and just this evening I found myself changing over a +/- 2 minute range with clearly audible results.  Not many arms can do this, and unless they can, cartridge performance suffers.

@terry9 - How do you measure these small angles and what tonearm are you using?  Isn't any tonearm capable of infinite azimuth settings if it has a rotating headshell (or rotating arm wand for linear trackers) that locks into position?

Thanks for agreeing with me, T9, but my point was not that the TT is most important; it was that flippant generalizations, like “differences between turntables…” are not helpful and may be misleading. And of course you can’t leave out the tonearm.

@pedroeb 

"Where do I get 3 phase when my house is only single phase? Surely AC motors are asking for trouble."

Two entirely different things.  Phase does not necessarily mean AC, and AC does not necessarily mean sinusoidal.  In these instances we're primarily talking about BLDC motors.

@lewm  Yes, what I wrote was ambiguous. I meant, "I agree with Lew (about TT and tonearm being important) AND TT is most important ...".

@pedroeb  Absolutely. Which is also why some mechanism of keeping the record flat is so important. Vacuum hold-down is effective but cumbersome, but a reflex clamp is just as good for most records.

@ketchup  My tonearm is an air bearing DIY with rock solid shafting and precision adjustments in all directions. The actual fine measurement of azimuth is from a fine scale counter marked in 100 micron increments, but capable of repeating to within 20 microns. Since the beam is 254 mm, resolution is calculated quite accurately by the small angle relation tan ~ sin ~ angle in radians, and 20 microns corresponds to about 30 seconds of arc. Adjustments on this scale are not sufficient to impair horizontality much at all, and so I have azimuth on the fly. Adjustment is secured by a brake.