Turntable speed stabilty

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The motor vibration can be synchronous with the rotation depending on your mains and motor type

50Hz 24 pole = 250rpm ie 7.5 rotations in 1.8s
60Hz 24 pole = 300rpm ie 9 rotations in 1.8s
50Hz 16 pole = 375rpm ie 11.25 rotations in 1.8s
60Hz 16 pole = 450rpm ie 13.5 rotations in 1.8s

Do you have a 24 pole motor (Linn etc) Scott?
 
The motor vibration can be synchronous with the rotation depending on your mains and motor type

50Hz 24 pole = 250rpm ie 7.5 rotations in 1.8s
60Hz 24 pole = 300rpm ie 9 rotations in 1.8s
50Hz 16 pole = 375rpm ie 11.25 rotations in 1.8s
60Hz 16 pole = 450rpm ie 13.5 rotations in 1.8s

Do you have a 24 pole motor (Linn etc) Scott?

I don't know but 9 looks right. I'll be checking it, this is sort of cool. It's a DC motor BTW but still the RPM's are fairly standard for interchangeability.
 
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I can see you are having fun, Scott. :up: This is turning into a very useful tool. Your cheap turntable shows a wobble between 999-1003 Hz more or less, right?

Yes, better than the other night without a run in. Belts are mechanical things and the concept of burn/run in is perfectly valid. I think I'll add an annotation for mean frequency so folks don't have to guesstimate it.
 
Position Trigger

Not sure if it is still required but I have created a position trigger/pulse on one stereo channel using a Hall Effect sensor. I initial though the AC coupling at the i/p to the sound card would differentiate the signal and make it unusable but the results look OK. The trigger shape is shown below and is 20mS wide.

TTPositionTrigger.png

If the pulse is suitable I can record a test tone on the other channel (left?) - please let me know.



Regards,
 
Not sure if it is still required but I have created a position trigger/pulse on one stereo channel using a Hall Effect sensor. I initial though the AC coupling at the i/p to the sound card would differentiate the signal and make it unusable but the results look OK. The trigger shape is shown below and is 20mS wide.

If the pulse is suitable I can record a test tone on the other channel (left?) - please let me know.
,

Looks fine and should be workable.
 
newbie question.
As Pano has said "wobble between 999-1003 Hz". How to interpret it in the polar plot ? The plot posted in #580 the green trace doesn't match at 0 degrees after one revolution. Does that mean wobble ? Sincere thanks for efforts done by everyone.
 
Two rotations will never exactly overlap as the test record is not perfect and external vibration is also getting involved
Not quite - two consecutive rotations won't exactly line up if the platter rotational period is not exactly the same as display rotational period. This cropped up earlier in discussion. For example, if the TT speed is slightly slow or fast.

In my SW, I included a 'display nudge' function button which can manually align traces, to be used to fix this effect if necessary.

LD
 
It matches very well and I can see 9 cycles of ripple on the circle.
Yes, that is common enough, but IMO it's generally a fault/opportunity for improvement in the drive system.

It need not happen in belt drive TTs; here's one of my own belt drive TTs from the archive - it's my own build 2kg solid platter outside drive, RB250 arm with custom arm damping and OM40. The test record was 45rpm, FWIW.

LD
 

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Not quite - two consecutive rotations won't exactly line up if the platter rotational period is not exactly the same as display rotational period. This cropped up earlier in discussion. For example, if the TT speed is slightly slow or fast.

LD

Scaling to the mean frequency would fix that, IME the difference in mean between two revs is far less than even 1 degree in the plot. Even so 1% is only ~4 degrees on the plot.
 
Wow, you guys never cease to amaze me!

I have tried to give Scott's script proper surroundings, I think it should work. However, I do not get an meaningful output. (see picture).

Since I have reason to believe that something is wrong with my deck, it would be nice if someone could

1) process my file 5.wav (rename 5.zip to 5.wav) circularplotwise

2) help my to sort out why I don't get a nice circular plot?

I recorded it with sox (32/96), resampled it to 16/48, and cut out the relevant piece - a 3 Khz testtone - in audacity, and then - this.

R.
 

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