Turntable speed control

[spiritofmusic]

Ack, that is a point I was considering re the TimeLine. Indeed, lps on my tt are specifically not optimised using a record weight or clamp of any kind.
So TimeLine (and Kuzma Strobi) off my list.
I’m down to the KAB and Monarch now as final choices.

 

[ack]

Ack, that is a point I was considering re the TimeLine. Indeed, lps on my tt are specifically not optimised using a record weight or clamp of any kind.
So TimeLine (and Kuzma Strobi) off my list.
I’m down to the KAB and Monarch now as final choices.

I can tell you from experience that the KAB is exceptionally accurate, as measured with a 1kHz test tone at the speaker terminals, so accuracy to 1/1000th indeed

 

[spiritofmusic]

Ack, I’ve just dipped in to your system thread.
50+ pages, that’s pretty good going.
Thanks for the KAB thumbs up.
Obviously a laser tach is by definition easier to read over a longer period, giving numerical readout to 3 places.
But I’m also aware it’s at closely spaced intervals (ie has to wait on each rotation for the laser to detect the tape marker on the platter), and so is not as real-time or in-the-moment as the KAB.

 

[spiritofmusic]

Settled on the KAB SpeedStrobe.
Couldn’t be happier.

 

[PeterA]

Settled on the KAB SpeedStrobe.
Couldn’t be happier.

Congratulations Marc. I also have a KAB along with a TimeLine. Could you post a video of your turntable being tested for speed while playing music? I started a database on the TimeLine thread and have always wondered about the speed accuracy and stability of rim drive turntables.

 

[Ron Resnick]

Congratulations, Marc. I have used the KAB for 20+ years. I still have it (somewhere, in deep off-site storage). I found it very simple to use. Assuming it is accurate it is a pretty good solution.

I am curious to try the TimeLine (but I don’t love the idea of affixing even a tiny device to the platter).

 

[PeterA]

Congratulations, Marc. I have used the KAB for 20+ years. I still have it (somewhere, in deep off-site storage). I found it very simple to use. Assuming it is accurate it is a pretty good solution.

I am curious to try the TimeLine (but I don’t love the idea of affixing even a tiny device to the platter).

The Timeline does not require you to fix anything to anything, Ron. It is a simple laser dot on the wall created by a record weight like device that you place over the spindle and play a record. You can watch the videos I made on my Timeline thread.

 

[Ron Resnick]

Sorry, Peter; my mistake. I am confusing it with another product.

I watched the Sutherland video, and it is indeed an interesting product. It is kind of like the inverse of the KAB where, instead of the device projecting a light, you project the light at the KAB sheet rotating on the platter. The KAB seems to me a little bit easier to use, but if the TimeLine is more accurate than it is worth the extra small effort.

It seems like the TimeLine would be more accurate than the KAB because you cannot use the KAB platter sheet with a needle in the groove.

 

[spiritofmusic]

Hi Peter, when I learn how to upload a video, I will.
My tt seems pretty speed constant, this KAB is a lot easier to use to check on this.

 

[PeterA]

Sorry, Peter; my mistake. I am confusing it with another product.

I watched the Sutherland video, and it is indeed an interesting product. It is kind of like the inverse of the KAB where, instead of the device projecting a light, you project the light at the KAB sheet rotating on the platter. The KAB seems to me a little bit easier to use, but if the TimeLine is more accurate than it is worth the extra small effort.

It seems like the TimeLine would be more accurate than the KAB because you cannot use the KAB platter sheet with a needle in the groove.

Both devices are easy to use. They measure slightly different things. Both can be used while playing a record with the stylus in the groove. The KAB checks speed in shorter intervals. The Timeline only once per revolution, but they both show stylus drag if your platter is effected by this. I set speed with the stylus playing the groove.

 

[morricab]

Both devices are easy to use. They measure slightly different things. Both can be used while playing a record with the stylus in the groove. The KAB checks speed in shorter intervals. The Timeline only once per revolution, but they both show stylus drag if your platter is effected by this. I set speed with the stylus playing the groove.

i haven't seen anything as "real-time" as the Allnic Speednic. I have one and it can be used while playing a record and you see instantly if needle drag is affecting the speed. Also, i have yet to find a belt-drive TT that was running truly at the right speed and not needing some adjustment...including Transrotor and SME TTs. It is very sensitive to very subtle speed variations. Great device...

 

[spiritofmusic]

I considered it Brad, but my tt is designed to be used without weight or clamp, w the lp suspended on Delrin points over the platter, so Allnic ruled out in my case.

 

[microstrip]

i haven't seen anything as "real-time" as the Allnic Speednic. I have one and it can be used while playing a record and you see instantly if needle drag is affecting the speed. Also, i have yet to find a belt-drive TT that was running truly at the right speed and not needing some adjustment...including Transrotor and SME TTs. It is very sensitive to very subtle speed variations. Great device...

Do you consider that an absolute steady deviation of 0.1% turntable rotational speed affects perceived sound quality? Or is even perceptible?

 

[awsmone]

Do you consider that an absolute deviation of 0.1% turntable rotational speed affects perceived sound quality? Or is even perceptible?

Are you referring to a steady state difference or fluctuations of 0.1%, and is



If fluctuations, yes most adults will hear that

400 hertz x 0.01%= 4 hertz

25 cents ie a quarter of a semitone is easily perceivable by vast majority of individuals

400 x(1+ 0.0005946x 25 cents) =405.95 hertz

So yes we could perceive that, for steady state however, few people would pick it unless perfect pitch

 

[microstrip]

Are you referring to a steady state difference or fluctuations of 0.1%, and is



If fluctuations, yes most adults will hear that

400 hertz x 0.01%= 4 hertz

25 cents ie a quarter of a semitone is easily perceivable by vast majority of individuals

400 x(1+ 0.0005946x 25 cents) =405.95 hertz

So yes we could perceive that, for steady state however, few people would pick it unless perfect pitch

Surely steady - we are very sensitive to fluctuations. Thanks I will edit my post.

 

[Phoenix Engineering]

i haven't seen anything as "real-time" as the Allnic Speednic. I have one and it can be used while playing a record and you see instantly if needle drag is affecting the speed.

Some thoughts on the use of strobe discs:

A crystal controlled light source is essential; using the wall outlet's line frequency will be inaccurate as the frequency varies over time.

The strobe disc will show fast or slow indication, but not a reading of how much fast or slow.

The larger the diameter of the indicator, the easier it will show speed variation. The Timeline projects its light source out to the walls of the room, so the radius could be 8ft or more. This will have much more resolution than a 12" disc, or in the case of the Speednic, 3.5" diameter. A 3.5" diameter disc will have ~11" circumference; at 33.333 RPM, the outer edge is moving at ~6.1086"/sec. A speed variation of +0.01RPM will complete one revolution 539.838µS faster than 33 1/3 RPM, so a line on the disc will move ~3.3mils in one revolution or about 1.832mils/sec, about half the thickness of a human hair or 20lb bond paper. I doubt that would be perceptible to the naked eye or without a fixed pointer and several if not many revolutions. A speed variation of +0.1RPM will move the lines at 18.271mils/sec, about half the thickness of a credit card. I would think that would be visible over several revs, with or without a fixed pointer.

The Sutherland Timeline does not illuminate a moving line on a disc for an indication, the pulse of light creates a moving line on the wall. This is an important distinction, as the line of light on the wall does not smear an image the way a strobe disc does, instead you look at the transition from light to no light to observe drift and the transition will be very sharp and distinct. The Speednic disc has 90 lines evenly spaced every 4°. At 33 1/3 RPM the disc is moving 200°/sec, so a 50Hz strobe light is needed (this will flash as each line moves 4° so the lines will appear stationary). If the strobe flash was 50% duty cycle, the line would smear for 2° as the line moves continuously and the light would be on for ½ the time and off for ½ the time. The duty cycle will need to be fairly short to give a "sharp" image but even at 1/32 duty cycle the line will smear for 0.125° or 3.8mils at the edge of 3.5" disc which is more than the error or drift per second at +0.02 RPM speed variation. The duty cycle then will limit the resolution as well as the disc diameter and the ability of the human eye to detect small movements over time.

A fairly accurate means of measuring platter speed is to mark the platter with a single piece of tape and count the number of revolutions in 3 minutes. 33 1/3 RPM will be exactly 100 revs in 3 minutes.

 

[Lagonda]

I hope my RoadRunner does not break. I love it !

 

[morricab]

Some thoughts on the use of strobe discs:

A crystal controlled light source is essential; using the wall outlet's line frequency will be inaccurate as the frequency varies over time.

The strobe disc will show fast or slow indication, but not a reading of how much fast or slow.

The larger the diameter of the indicator, the easier it will show speed variation. The Timeline projects its light source out to the walls of the room, so the radius could be 8ft or more. This will have much more resolution than a 12" disc, or in the case of the Speednic, 3.5" diameter. A 3.5" diameter disc will have ~11" circumference; at 33.333 RPM, the outer edge is moving at ~6.1086"/sec. A speed variation of +0.01RPM will complete one revolution 539.838µS faster than 33 1/3 RPM, so a line on the disc will move ~3.3mils in one revolution or about 1.832mils/sec, about half the thickness of a human hair or 20lb bond paper. I doubt that would be perceptible to the naked eye or without a fixed pointer and several if not many revolutions. A speed variation of +0.1RPM will move the lines at 18.271mils/sec, about half the thickness of a credit card. I would think that would be visible over several revs, with or without a fixed pointer.

The Sutherland Timeline does not illuminate a moving line on a disc for an indication, the pulse of light creates a moving line on the wall. This is an important distinction, as the line of light on the wall does not smear an image the way a strobe disc does, instead you look at the transition from light to no light to observe drift and the transition will be very sharp and distinct. The Speednic disc has 90 lines evenly spaced every 4°. At 33 1/3 RPM the disc is moving 200°/sec, so a 50Hz strobe light is needed (this will flash as each line moves 4° so the lines will appear stationary). If the strobe flash was 50% duty cycle, the line would smear for 2° as the line moves continuously and the light would be on for ½ the time and off for ½ the time. The duty cycle will need to be fairly short to give a "sharp" image but even at 1/32 duty cycle the line will smear for 0.125° or 3.8mils at the edge of 3.5" disc which is more than the error or drift per second at +0.02 RPM speed variation. The duty cycle then will limit the resolution as well as the disc diameter and the ability of the human eye to detect small movements over time.

A fairly accurate means of measuring platter speed is to mark the platter with a single piece of tape and count the number of revolutions in 3 minutes. 33 1/3 RPM will be exactly 100 revs in 3 minutes.

I agree with the numbers you have run; however, the smearing would only be determinable if the pulse length of the strobe flash is known. This is likely in the low mircoseconds. An overall duty cycle of 50hz means one flash every 20 mS. If the strobe duration is 2 microseconds then the duty cycle is actually only 0.002 ms/20ms *100 = 0.01% and not 3.125% as you have proposed. This would make the smear negligible, IMO and a drift of smaller amounts than you propose whould be possible. The lightsource on the Speednic is crystal controlled as it is battery powered. I am not saying its perfect but I have seen that most TTs are off absolute or fluctuate under load while using it.

 

[Phoenix Engineering]

Yes, it would help to know what numbers the SpeedNic is using. I would doubt the duty cycle is as short as you proposed, but it is technically feasible and possible. On the RR tach, there is a built in software triggered stobe that I used during development to check for trigger ambiguity, and never removed in production. The pulse width of my strobe was 300uS and required a very bright white LED run at higher current than normal to be visible. Even at 300uS, the flash does not appear very bright. The brightness of the LED is directly proportional to the current. For a single ended pulse (PWM) the RMS value of current will be sqrt(duty cycle), so in your example the brightness would be sqrt(1/10,000) or 1% or normal.

My purpose for crunching the numbers in the previous post was to illuminate the fact that strobe disks can have limited resolution, especially when using an ambient light source, and the difference between the Timeline and a normal strobe disk, even if using a crystal controlled source.

 

[Ron Resnick]

Yes, it would help to know what numbers the SpeedNic is using. I would doubt the duty cycle is as short as you proposed, but it is technically feasible and possible. On the RR tach, there is a built in software triggered stobe that I used during development to check for trigger ambiguity, and never removed in production. The pulse width of my strobe was 300uS and required a very bright white LED run at higher current than normal to be visible. Even at 300uS, the flash does not appear very bright. The brightness of the LED is directly proportional to the current. For a single ended pulse (PWM) the RMS value of current will be sqrt(duty cycle), so in your example the brightness would be sqrt(1/10,000) or 1% or normal.

My purpose for crunching the numbers in the previous post was to illuminate the fact that strobe disks can have limited resolution, especially when using an ambient light source, and the difference between the Timeline and a normal strobe disk, even if using a crystal controlled source.

Thank you very much for posting here, Phoenix Engineering! Your participation is greatly appreciated!