According to the article "Cutting LPs, the Theory" published in Studio Sound 1975-07, "The frictional force acting on the stylus point pulls the stylus point in the direction of the groove motion with a force of about 25% of the playing weight (tracking force)". However, as the following video shows, the drag from the LP groove is continuously variable, which if there is no speed servo, could conceivably cause modulation of the platter RPM according to the instantaneous dynamics and frequency content of the music. https://www.youtube.com/watch?app=desktop&v=j0ZuukxmaVM |
While theoretically true there is an important variable that will differ from one table to the next and that is the inertia of the platter. The increase in friction heavy modulation would cause is transient and it takes a certain amount of time to change the rotational speed of the platter depending on how heavy the platter is. Short increases in friction will have little effect on a heavy platter. Longer increases will be countered by a good turntable's drive system. This is the reason most turntable manufacturers use AC synchronous motors. Any slowing of the motor causes an instantaneous increase in torque maintaining platter speed.
fusian, if you want to be accurate about it you have to make a "puck" that fits on the platter's spindle just 2-3" in diameter so that your phone can lie flat over the platter. Then, you have to mark the phone and puck to index the position of the phone so that you are putting it down in the exact same position every time. |
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Thanks Jonathan @jcarr for posting video in Russian :) This time only I can fully understand it without goodle translate or subtitles :) Interesting.
He’s using Soviet Melodiya test record and Soviet Corvette cartridge with elliptical tip (1.5g tracking force). |
The inertia of the platter, the torque available from the motor, the particular musical passage, the position of the stylus on the LP surface relative to the spindle, the cartridge, etc., etc. These are all factors that would influence any measurement of stylus drag. So to begin with, we would all have to agree on one particular LP pressing and on one particular passage on that LP surface. Then, since it is impossible for us all to be using the same cartridge, at least we could agree on one stylus shape for all of us. VTF Also affects friction. These are all things that we would need to agree upon a priori to obtain data that are remotely comparable, and there’s more I haven’t thought of yet. But, Mijostyn, platter inertia is a variable that figures in to the result. Of course it would make a difference, but of course that is what we are looking for. |
At the risk of ruining everyone's fun it seems to me that the desired outcomes for this set of measurements could easily be overcome by the simple expedient of a simple listen. If our ears can discern some sort of smearing or loss of detail, then the matter is resolved. If not, then it does not matter. One word of caution. The OP mentioned lubrication via beer, and the music of Mahler. I see no problem with the lube, but too much Mahler could obfuscate the veracity of the outcome. ;-)
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Not that I care a lot, but I disagree that actual data would be worthless. I think it would be interesting. However I do not think it will ever happen because of the necessary controls that we really as a group cannot put into affect. |
Clearaudio has a speed record that you play when adjusting the speed of the platter |
You're kidding me, right? Idler is the best? You must listen to a lot of cassettes, too.
As for stylus drag, you can see it on a turntable with a strobe.
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As @lewm points out, lots of variables. But at least one measurement isn't hard: Analogue Productions test record 1 KHz tone, running into a frequency counter.
Control condition: with platter up to speed, disconnect motor and measure the time required to run down from 1000 Hz to about 900 Hz with stylus engaged for 1 second out of every 10 seconds, giving a good approximation to '90% stylus not engaged').
Experimental condition: time to same frequency drop with stylus fully engaged.
In this way differentiate bearing friction from stylus friction. Easier for me, as my air bearing is virtually frictionless. |
Seriously, are you aware of this strobe control ? Any change in speed is immediately visible! If 33 1/3 rpm or 45 rpm rotation speed is not stable the dots on the strobe control are not stable too, very simple, and it was on Technics direct drive since the 70s. And you don’t need any special devices at all ! Just buy yourself a turntable with a proper direct drive motor (they are very powerful). |
Better to buy the KAB strobe disc and the battery powered strobe light that goes with. Can use with any TT and is much more accurate than any built in strobe on our vintage DD TTs. But that will only give you a qualitative answer that you can verbally relate to others, not hard data.The KAB strobe disc is about 7 inches in diameter. So, you can run the strobe disc on top of a 12 inch LP with the stylus in the outer grooves of the LP, to get an idea of the effect of stylus drag. |
An off board strobe such as the KAB Keystrobe and Disc to show 50hz(100 flashes per second) or 60hz(120 flashes per second), as it is powered by a built in power supply designed to offer a correct amount of flashes for each frequency, it will be a very accurate method to check for rotation speed consistency/inconsistencies.
Additionally it will not be effected by fluctuation in a Hz reading that can occur in a Power Line.
The flashes on a TT's built in strobe will be effected by the syncing to the Power Line Hz frequency being received by the TT, and the built in strobe will usually offer a visual where the demarcated increments appear to be stationary, but this reading can prove to be insufficient to offer the most accurate RPM reading.
I'm confident that in a past investigation there has been information discovered that has claimed certain Strobe Bulbs or LED only function at their correct per second rate when the mains Hz is very accurate at the TT. |
+1 to what pinDAC wrote. A big advantage of the KAB is battery power. |
In two days I'll be able to see how the Eclipse drive system handles things down to 1/1000th of a revolution on it's own rev counter. More accurate than any phone app? |
Yes, the tachometer will show you the frequency of speed correction that is needed to maintain 33.333 rpm in spite of stylus drag, in addition to actual platter speed. The Eclipse add on is constantly correcting for such forces. When there is a lot of drag, the indicator LED blinks more frequently and the speed momentarily sags. But usually by less than 1.0 rpm. At least that’s how my Phoenix Eagle plus Roadrunner works. |
