Luca Sorrentino
Member
Introduction
I’ve had a Vernier force sensor for educational use for a couple of years, acceleration and gyroscope. I didn’t have time to play with it until a couple of weeks ago, it connects via Bluetooth and can collect up to 1000 samples per second, here, acquiring the data, 5 minutes of data therefore 300,000 samples, on turntables with different technology and in different state of conservation I was able to make the most precise measurement of wow and flutter that I happened to be able to do and see.
Measurement was made on the turntable alone, so it does not include imperfections in reading and printing of the test disc and resonances of arm/cartridge system, the sensor was first balanced, the data is saved in CSV with its native app, I first examined them with LTspice, a program that I always use and that I know, then with a couple of Python scripts that I specifically created.
Most interesting things, which I was able to see are:
Have been tested:
In conclusion
Complete maintenance is also important for DD turntables, it doesn't matter what the service maual says, nor the fact that they lock the correct speed by turning on the "quartz locked" light. If you want the declared performances you have to disasseble, clean, lubricate, carry out service calibrations and measure before and after the treatment, to verify the effectiveness of the interventions.
I’m sorry I don’t have a belt drive turntable at hand, I have some but they have been stopped for a long time, I would be curious to measure a high-end one (mine are not), I think it would win at the test bench.
I now understand those who use the Lenco platter by putting the mechanics on a new base and changing the tonearm.
The DDs I measured are more precise in nominal speed but dirty the frequency spectrum more by “vobulating” the signal in some way. Is it audible? What is the acceptable limit? I don’t know, and I can’t make a direct comparison between these turntables since they have different arm and cartridge, and then it would only be a subjective opinion strongly influenced by my preferences and beliefs.
The W&F weighting curve was made several decades ago, when technologically outdated devices were available, I am not entirely convinced that the dirt in high frequency is to be considered less important than that at 4Hz, the maximum sensitivity according to the IEC386. If so, the jitter of digital devices would have no importance, and it doesn’t seem correct to me.
It is possible, if I can I will try to do it, that these measurements can also be obtained with the gyroscope of the mobile phone, I will try sooner or later.
The sensor https://www.vernier.com/product/go-direct-force-and-acceleration-sensor/
Lenco wins above all, its fundamental at 0.555Hz is placed at -70dB the highest in this test, but it is the one that matters and disturbs the least, consider that a 25 micron decentralized disc is enough to obtain the same "degradation". Close to 0Hz the noise floor rises, it is the speed which, being mechanical, is not very precise, but still within 2 points per thousand. Above 6Hz you see absolutely nothing.
Note the dynamic range of the measurement, between the 0dB (I normalized to 33 and 1/3) of the continuous rotation and the noise floor there are 110dB!
Sansui and Lenco overlapped for direct comparison. This one is clean too, DD four coils effect is dominant, can’t understand what happens at half the freq rotation of the platter.
The Revox has several defects, motor cogging stands out, there are no adjustments, trimmers to compensate for the asymmetries of the two driving circuits, nor to compensate for drift and differences that the Hall sensors could have accumulated over the years, hfe differences of power transistors.
I widen to 120Hz because the Revox, the only one tested, has a component at -90dB 111Hz, I guess the unshielded tachometer cables as the root cause. Not measurable with the means of the time, the German is the one with the most spartan electronics, the Japanese were much more cutting edge.
The Sony has never been serviced and it shows. It probably has an imperceptible ticking, an impulsive braking on the lap that the control immediately puts back on its feet. More precise RPM. Ticking evidence in polar diagram.
The results of the script that calculates weighted W&F and not of Lenco and Sansui, the Sansui was also measurable at the time via the tachymetric freq, the Lenco was not, it has performances much much higher than those declared.
The crowding of harmonics (however very low value) of the Sony that is slightly defective, the cogging at the frequencies that weigh more for the Revox. The Sony can be improved with the right maintenance, probably the Revox too by adding trimmers to balance the two motor control branches, that will be for another time. Who knows how much that spurious at 111.11Hz weighs, it's a kind of periodic jitter.
The gray circle labeled 1.000 (covered by the graph) is the speed normalized to 33+1/3, the inner one a thousandth less, the outer one 1/1000 more. Graphs are obtained by processing the average of 50 rotations.
The repeated acceleration and braking of the Revox are due to the geometry of the motor and the asymmetries of the driving circuit.
The Lenco simply brakes and accelerates smoothly during the turn. Would re-milling the bottom of the platter also remove this "defect"? Also note the slight positive deviation from the nominal speed.
The variations of the Sansui are softer and at low frequency, the 4 lobes are the 4 coils of the stator.
The Sony would win hands down over other DDs if I serviced it.
Brief recap.
I’ve had a Vernier force sensor for educational use for a couple of years, acceleration and gyroscope. I didn’t have time to play with it until a couple of weeks ago, it connects via Bluetooth and can collect up to 1000 samples per second, here, acquiring the data, 5 minutes of data therefore 300,000 samples, on turntables with different technology and in different state of conservation I was able to make the most precise measurement of wow and flutter that I happened to be able to do and see.
Measurement was made on the turntable alone, so it does not include imperfections in reading and printing of the test disc and resonances of arm/cartridge system, the sensor was first balanced, the data is saved in CSV with its native app, I first examined them with LTspice, a program that I always use and that I know, then with a couple of Python scripts that I specifically created.
Most interesting things, which I was able to see are:
- spectrum of speed variation, with a resolution, at least by me, never seen
- polar diagrams of speed variation
Have been tested:
- Lenco L75 revised and lubricated.
- Sansui XP-99 revised and lubricated.
- Sony PS X555 ES NOT revised in the engine part.
- Revox B790 revised and lubricated.
In conclusion
Complete maintenance is also important for DD turntables, it doesn't matter what the service maual says, nor the fact that they lock the correct speed by turning on the "quartz locked" light. If you want the declared performances you have to disasseble, clean, lubricate, carry out service calibrations and measure before and after the treatment, to verify the effectiveness of the interventions.
I’m sorry I don’t have a belt drive turntable at hand, I have some but they have been stopped for a long time, I would be curious to measure a high-end one (mine are not), I think it would win at the test bench.
I now understand those who use the Lenco platter by putting the mechanics on a new base and changing the tonearm.
The DDs I measured are more precise in nominal speed but dirty the frequency spectrum more by “vobulating” the signal in some way. Is it audible? What is the acceptable limit? I don’t know, and I can’t make a direct comparison between these turntables since they have different arm and cartridge, and then it would only be a subjective opinion strongly influenced by my preferences and beliefs.
The W&F weighting curve was made several decades ago, when technologically outdated devices were available, I am not entirely convinced that the dirt in high frequency is to be considered less important than that at 4Hz, the maximum sensitivity according to the IEC386. If so, the jitter of digital devices would have no importance, and it doesn’t seem correct to me.
It is possible, if I can I will try to do it, that these measurements can also be obtained with the gyroscope of the mobile phone, I will try sooner or later.
The sensor https://www.vernier.com/product/go-direct-force-and-acceleration-sensor/
Lenco wins above all, its fundamental at 0.555Hz is placed at -70dB the highest in this test, but it is the one that matters and disturbs the least, consider that a 25 micron decentralized disc is enough to obtain the same "degradation". Close to 0Hz the noise floor rises, it is the speed which, being mechanical, is not very precise, but still within 2 points per thousand. Above 6Hz you see absolutely nothing.
Note the dynamic range of the measurement, between the 0dB (I normalized to 33 and 1/3) of the continuous rotation and the noise floor there are 110dB!
Sansui and Lenco overlapped for direct comparison. This one is clean too, DD four coils effect is dominant, can’t understand what happens at half the freq rotation of the platter.
The Revox has several defects, motor cogging stands out, there are no adjustments, trimmers to compensate for the asymmetries of the two driving circuits, nor to compensate for drift and differences that the Hall sensors could have accumulated over the years, hfe differences of power transistors.
I widen to 120Hz because the Revox, the only one tested, has a component at -90dB 111Hz, I guess the unshielded tachometer cables as the root cause. Not measurable with the means of the time, the German is the one with the most spartan electronics, the Japanese were much more cutting edge.
The Sony has never been serviced and it shows. It probably has an imperceptible ticking, an impulsive braking on the lap that the control immediately puts back on its feet. More precise RPM. Ticking evidence in polar diagram.
The results of the script that calculates weighted W&F and not of Lenco and Sansui, the Sansui was also measurable at the time via the tachymetric freq, the Lenco was not, it has performances much much higher than those declared.
The crowding of harmonics (however very low value) of the Sony that is slightly defective, the cogging at the frequencies that weigh more for the Revox. The Sony can be improved with the right maintenance, probably the Revox too by adding trimmers to balance the two motor control branches, that will be for another time. Who knows how much that spurious at 111.11Hz weighs, it's a kind of periodic jitter.
The gray circle labeled 1.000 (covered by the graph) is the speed normalized to 33+1/3, the inner one a thousandth less, the outer one 1/1000 more. Graphs are obtained by processing the average of 50 rotations.
The repeated acceleration and braking of the Revox are due to the geometry of the motor and the asymmetries of the driving circuit.
The Lenco simply brakes and accelerates smoothly during the turn. Would re-milling the bottom of the platter also remove this "defect"? Also note the slight positive deviation from the nominal speed.
The variations of the Sansui are softer and at low frequency, the 4 lobes are the 4 coils of the stator.
The Sony would win hands down over other DDs if I serviced it.
Brief recap.
