TT speed


When I use a protractor to align the stylus I do the alignment at the inside, and then rotate the platter maybe 20 degree when I move the arm to the outside of the LP, or protractor.

On a linear tracking “arm” it would not need to rotate at all.

At 33-1/3, then 15 minutes would be about 500 rotations. And that 20 degrees would be a delay of 18th of a rotation.

So a 1 kHz tone would be about 0.11 Hz below 1000.
It is not much, but seems kind of interesting... maybe?

128x128holmz

Showing 6 responses by dover

Everywhere at any point on this LP, the 1000Hz test tone has been encoded by a perfect cutter lathe.  In practice, the stylus tip is just a point on the surface of the LP; it doesn't "know" where it was a fraction of a second before or after any particular event.  How can this phenomenon change the fundamental frequency?  

The cutter lathe is moving in a straight line.

A pivoted arm is moving in an arc.

They are not congruent.

Does your direct drive turntable speed up and down to bridge the gap on each rotation ?

 It also disproves your fantasy that phono cartridge tangency affects frequency. 

I have never claimed that.

What I have said is that the stylus on a pivoted arm, for each 1.8 seconds, deviates from the position of the cutter head at the same time interval.

Frequency is a red herring because the deviation would be so small it would probably be less than that generated by normal tt issues around stability.

 

Assuming a perfect test record, you could playback a pure 1kHz tone from the beginning of the LP to the end. Any deviation would be the result of the turntable’s w&f, not any "translocation of the stylus."

That statement is not correct.

Holmz is correct - on a pivoted arm the stylus is advancing and retarding relative to tangent, therefore there must be a timing error, but it will be minuscule on rotation re adjacent grooves.

@cleeds 

Your belief is easily disproved with a test record - it’s easy to measure the frequency of a test tone on an LP.

We've already shown that measurements reveal it doesn't exist. It's easy to measure a 1 kHz tone on a test record.

Unfortunately you can't see the wood for the trees.

If you draw a line across the 2 null points of a pivoted arm, and are using Baerwald for example, then at the beginning of the record the stylus is behind the line, as it crosses the first null point it will move ahead of the line, and then as you cross the second null point it will fall behind the line.

Assuming the record is travelling at constant speed, then the motion of the stylus forward and back relative to the line must alter the apparent speed, as seen from the record groove, albeit minuscule.

Your fervour for FFT analysis appears to be an impediment to understanding basic maths and physics.

 

@holmz

but does put “another one” in the clip of the digital crowd’s ammo against analogue.

I have a friend who designs DAC’s way beyond what is available publicly.

His description of red book digital is "it is only a little bit out ALL of the time".

Without going into the weeds truncation errors due to the sine x/x calculation are built into the red book standards. Digital data transfer also contains errors in transmission - it is possible to fix these as each packet has a check digit, but you would need a Fugaku supercomputer to calculate the corrections in real time.