The only way to adjust the speed on an AC motor is vary the frequency of the AC which powers the SME 10. To do this, you will need an external motor controler like the Walker or VPI SDS. |
Or, Peter, a Variac, as we described. They are available on ebay or easily from scientific supply houses if you would like a used one.
Best to You in your Search,
David
|
A Variac will not work to adjust the speed of an AC motor. AC motors are synchronized with the frequency of the AC supply current. A variac only alters the voltage, not the frequency. |
You may be worrying needlessly Peter?
It is not necessary to have the turntable revolve at precisely 33.33rpm to have good sound.
Orchestras around the world don't always base their pitch on the note A being at 440Hz. Anywhere +or-12Hz in pitch is quite acceptable.
This would relate to a shift in the Timeline mark on the wall of up to 1/2" every revolution of the platter.
As long as this shift is consistent.......you will have no speed-related issues.
The only way to find out....is to buy/borrow a Timeline.
The 'fear' is much worse than the knowledge :^)
Good luck. |
This would relate to a shift in the Timeline mark on the wall of up to 1/2" every revolution of the platter. To make that statement, you also need to state the distance between the Timeline and the wall, don't you? At what distance from the wall does 1/2" of shift per revolution correspond to +/- 12Hz? |
Agree with Ketchup,
Imagine the wall being 30 feet away versus only 2 feet away. The greater the distance to the wall, the more pronounced any drift of the Timeline dot from a starting reference point Simple geometry.
Halcro,
I see your point. I can't hear a tiny pitch deviation from 440 Hz. And I don't hear problems with speed changes during heavy passages due to stylus drag, so perhaps it is not an issue. I sleep well not testing with the Timeline, but these threads are starting to get me worried, perhaps needlessly.
I think the newer SME motor controller which replaced the older rectangular/front dial type is available for my SME 10 and it has variable speed. It seems this would be a simpler solution than buying the Walker or VPI. I will look into the new SME controller.
Can anyone verify this? |
Of course you're both correct :-)
The distance from the spindle to the wall in my example above.....is 350mm.
The problem with stylus drag is that one doesn't consciously hear it.
From all that I have seen, read and heard over the last 6 months........I imagine that the majority of turntable users might be experiencing this phenomenon and are quite happy?
It is only really when one hears the complete elimination of any speed inconsistency that an epiphany occurs? |
I calculate the speed error by using the distance difference between the two timeline marks over one revolution. Using a radius of 350mm, the circumference at that distance is 2199mm. That means a 1/2", or 12.7mm per revolution drift is a speed error of 12.7/2199*100, or 0.5775%. At 440 Hz, the frequency is off by 2.54 Hz. If the two laser marks were on top of each other after one revolution, then the drift is zero and the speed error is zero. |
Sorry Tony,
Whilst I measured the distance from the turntable spindle to the wall at 350mm at right angles.....the laser line was actually projected approx. 400mm from the spindle to the wall at approx. 30 degrees.
Everything I said was approximate not expecting anyone to actually do the maths?
This was just to give Peter some relativity to his concerns :-)
Incidentally.....+6Hz from 440Hz @33.33 is 33.41rpm
+12Hz from 440Hz @33.33 is 33.48rpm
-6Hz from 440Hz @33.33 is 33.25rpm
-12Hz from 440Hz @33.33 is 33.18rpm |
Hi Halcro,
I do not quite understand how the platter speeds given correlate to the +12Hz, -12Hz and +6 Hz and -6 Hz shift from 440 Hz. 12 Hz out of 440 is a 2.73% variation. That means the platter speed must vary 2.73% as well. So I would expect platter speed to be 34.24 rpm to shift a 440 Hz tone by 12 Hz to 452 Hz. What am I missing? |
Hi Tony,
I'm not into the maths :-)
I'm simply quoting the read-outs on the digital display of the TT-101 as I change the pitch in 6Hz increments.
Perhaps someone can help with the correct calculations? |
Perfect timing. I actually just made a calculator in Excel for the Sutherland Timeline. You enter the distance to the wall and the laser deviation per revolution and it gives you the circumference of the virtual circle that the laser travels, the speed error of your platter in percent, the RPM your platter is off by, and the actual RPM of your platter. It can also tell you how many Hz a given frequency is off by.
Let me know if you would like to try it out! |
Ketchup ~ can you send me the spreadsheet you designed?
Thank you, very much appreciated in advance. |
Sksos1 and anyone else who wants the calculator,
Please send me an email through Audiogon and I'll attach the calculator to my response. |
