Strobe instability

[Sam Cogley]

My comment about direct drives was based not just on the experience of moving platters where you can feel a pulsation, but also on the tendency of the motors without platters to move in very jerky fashion if at all. And if you have taken direct drives apart, you've seen that there are a bunch of coils -- usually six or more, but not an infinite number, and certainly less than in even a low end stepping motor. So I don't have any doubt that the drive is not completely uniform. That doesn't mean its audible. But the wobble in the strobe is visible in mine and I wonder about it.
Specifically my comment was prompted by your mentioning that you had the same problem on all five of your tables and nothing changed when you used the variac. It wasn't solely based on your single apparently damage table. Maybe I misread your post, but it sure sounded like you were wondering about the same thing I'm wondering about.

I've been having a lousy day, sorry if I sounded rather snappish. Yes, I've wondered about that apparent fluctuation, but it's not audible and the W&F specs on any of these are as good or better than most anything else made. On all of mine (including the X70) they spin very easily without the platter. The Sonys actually go into runaway without the platter for speed regulation.

 

[MelodyMaster]

Any flutter caused by coil cogging on a Direct drive turntable would be too subtle to appear on a strobe. The ear would detect it as a distant or echo-y overtone on piano. And believe me, my Technics SL-110A or the SL-1200's are NOT cogging, no way, it doesnt happen. However some Hitachis and other DC motor decks of the late 60s did exhibit that a bit. But then belt drive decks have their problems with speed wander as the belt climbs up and down a bit, and idler decks of course have rumble. In every case the inherent, potential downside of each technique can be minimized by good (and expensive) design.