Platter slowdown caused by stylus drag on modulated grooves - diyAudio
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Old 28th June 2004, 06:00 PM   #1
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Default Platter slowdown caused by stylus drag on modulated grooves

Hi.

There seems to exist a concensual agreement that heavily modulated grooves have the efect to increase stylus drag resulting in a platter slowdown (among those that believe there is an efect). I've seen several diferent explanations for this, but so far was unable to find references to an authorative paper on the matter.

Does anyone know if such a paper exists, or if someone was actually able to measure it ?

And has anyone ever considered the opposite - the stylus leaving a modulated grove and entering the space between tracks actually having the efect of slowing the platter down ?

PS: I am aware of Mr. Cole's paper in JAES and RCA's response in the same journal. In fact, RCA states that it was unable to measure the efect.


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Old 28th June 2004, 06:24 PM   #2
sreten is offline sreten  United Kingdom
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Having heard a very poor (and cheap) turntable with dc drive
and a laughably lightwieght platter seriously changing pitch
depending on groove modulation you can be sure the effect
exists.

However with decent platter mass the effect is minimal and
automatically compensated for with AC synchronous motors.

It was an issue with cheaper servo turntables (direct drive or DC
motors) with lightwieght platters, the servo overcompensating
and causing "dynamic wow", the overcompensation due to
optimising wow and flutter on steady tones.

With AC synchronous motors (and properly designed servo's)
there is no opposite effect (which I presume you meant to
say speeds up the platter).

The effect is minimal with decent platter mass and correct motor
control, but by the laws of physics it must exist to some degree.

sreten.
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Old 28th June 2004, 08:08 PM   #3
docjoe is offline docjoe  Europe
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Hello Guilherme and Sreten
I have a Telarc LP wich was famous for its recording of 16 real canon shots in Tchaikovski's 1812 Overture. that was in 1980.
My turntable, a the time, I do not remember which one, did not slow down, instead the stylus poped out of the grove and crashed down in an adjacent grove. it was a denon dl103 on a mission 774 original tonearm, playing at 2g downforce without damping.
i did not play the record again until now, in fact until your thread showed up, i had even lost track of that lp.
I'll give it a run and tell the world!
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Old 28th June 2004, 08:52 PM   #4
sreten is offline sreten  United Kingdom
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Quote:
Originally posted by docjoe
Hello Guilherme and Sreten
I have a Telarc LP wich was famous for its recording of 16 real canon shots in Tchaikovski's 1812 Overture. that was in 1980.
My turntable, a the time, I do not remember which one, did not slow down, instead the stylus poped out of the grove and crashed down in an adjacent grove. it was a denon dl103 on a mission 774 original tonearm, playing at 2g downforce without damping.
i did not play the record again until now, in fact until your thread showed up, i had even lost track of that lp.
I'll give it a run and tell the world!
Silly modulation levels are hardly the point, if your turntable
has any issues with dynamic drag it will show up on all records
played as pitch instability or "dynamic wow". The effect is due
to variable dynamic drag, high levels of drag are not relevant.

sreten.
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Old 28th June 2004, 11:35 PM   #5
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sreten,

I'm not questioning the efect. On the contrary, I'm pretty sure it does happen. I'm just trying to find a paper where it is properly documented and/or measured.

I did meant what I said. As the stylus moved from the end of one song, through the silent grooves onto the next song, the platter would very slightly decrease speed and then go back up again.

Yes a synch motor will be as stable as the freq feeding it (well, almost) and if you slow it down it will loose synch with very notorious efects.
But, on a very tiny scale, platter speed is not a constant, but rather a series of "ups and downs". I believe this is because the belt has some elasticity which acts like a spring. And, at that scale, stylus drag is noticeable even when the platter is driven by a synch motor.

docjoe: be careful with those cannons


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Old 29th June 2004, 02:55 AM   #6
sreten is offline sreten  United Kingdom
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Quote:
Originally posted by GUILHERME
I did meant what I said. As the stylus moved from the end of one song, through the silent grooves onto the next song, the platter would very slightly decrease speed and then go back up again.
J.Guilherme
Why on earth would it do that ?

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Old 29th June 2004, 09:45 AM   #7
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Quote:
Why on earth would it do that ?
Exactly !

But what if someone had consistently measured just that ?...


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Old 29th June 2004, 01:00 PM   #8
sreten is offline sreten  United Kingdom
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Quote:
Originally posted by GUILHERME

Exactly !

But what if someone had consistently measured just that ?...

J.Guilherme
Huh ? what if they hadn't consistently measured just that.

I can't come up with a single arguement why it should slow
down, and can come up with a very reasonable arguement
that it will very slightly speed up between record tracks.

There nothing exact about pure conjecture, and without
any evidence or plausible theory as to why it might happen
the only sensible position to take is that it does not slow
down slightly between tracks.

If anything it almost certainly slightly speeds up.

sreten.
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Old 29th June 2004, 08:58 PM   #9
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sreten,

Thanks for your input. Indeed it's hard to think of a reason why the platter would slow down instead of speed up.

If you or anyone else does remember of any publications regarding this matter, please let me know.


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