Turntable speed question........

[JoeDJ]

I just checked my TT speed with a couple of of DL/printed strobe disks for 60hz.

There is absolutely no "wow".
However, it shows that both speeds are slightly slow by the same exact amount .....probably not enough to even notice.
This is with a new belt, clean pulley and platter... everything lubed and spinning freely.

So I checked my hz and discovered that it's 59.9 hz
My 66 year old brain is having a freeze....... Would that account for the slightly slow reading. or, would that make it appear faster?

 

[DUG]

Is your motor a 60Hz induction type?

If it is then it will track your strobe and always appear slow...drive ratio issue.

If it is some other type of drive that is not derived from line frequency then it would show faster than 59.9Hz if actually accurate.

Either way it seems that it is actually slow.

 

[Conrad Hoffman]

Your line frequency is probably far closer to 60 than 59.9; how good is your counter? Being belt drive, small errors in platter speed are likely. It's almost impossible to get the belt thickness just right for the pulley diameters so the platter speed comes out with no drift.

 

[sextaafondo]

If you feel you can, stick very very evenly one or two scotch tape turns around the motor pulley, then reinstall the belt and check speed. If done correctly should not wow at all and hopefully the speed will be spot on.

 

[JoeDJ]

I found the problem.

The belt guide to change speeds was hitting the belt ever so slightly in both 33 and 45.

Pulling the lever back slightly so the guide does not hit the belt brings the speed up to perfect. .

Tomorrow I will see what I have to do to adjust it to bring it down a hair. .

 

[JoeDJ]

Actually, I think that the motor pulley just has to be brought up a hair .

Probably the the rubber on the motor suspension had shrunk just enough over the years to allow the motor and pulley assembly to drop down slightly.
Maybe there's an ajustment for that .

 

[AndrewT]

A strobe that operates at mains frequency will always track mains frequency.
The turntable will hopefully turn at the correct speed/frequency.
If this frequency is "locked" to the mains frequency, then the strobe will ALWAYS indicate the SAME speed error.

Only when the TT speed and/or the strobe speed are NOT locked to mains frequency will the strobe indicate changes in the relative speed of strobe to TT rotation.

 

[JoeDJ]

As it turns out, the motor suspension was fine .
I had to raises the pulley a hair and bend the guide away from the belt a bit..
Speed is now fine.

I also played some piano and did not notice any flutter.

 

[tinitus]

as I remember it, a tiny bit slower speed gives better timing, rythm, and 'sonics'

or ... maybe its really the opposite
just a tiny bit too fast, and all the good musical stuff is gone

and I believe that is a main problem with all modern music 'reproduction'
but with new and better digital technology this may be changing soon

 

[kevinkr]

Best IMO to playback at the proper speed, obviously if the cutting lathe was running off speed all bets are off unless you have some range of adjustment and know by pitch whether you are on speed or not.

I don't buy that playing off speed is going to be an improvement, but small errors are probably undetectable in practice.

Back when I was restoring my MIT flea TD-124/I basket case I used it as a source for an audio get together, it was running several % slow and while I could tell, apparently I was the only one - the strobe and speed adjustment linkages were not fitted at that time and I had to adjust it manually with a vinyl engine strobe I printed out for the occasion.. The strobe confirmed it was running slow, and reaching under the table to adjust it was a royal pain. Lots of curious looks and comments from the well beered crowd.. lol

 

[stratus46]

I just checked my TT speed with a couple of of DL/printed strobe disks for 60hz.

There is absolutely no "wow".
However, it shows that both speeds are slightly slow by the same exact amount .....probably not enough to even notice.
This is with a new belt, clean pulley and platter... everything lubed and spinning freely.

So I checked my hz and discovered that it's 59.9 hz
My 66 year old brain is having a freeze....... Would that account for the slightly slow reading. or, would that make it appear faster?

Unless you're running your own generator, it is NOT 59.9 Hz. To be on the power grid, the generators are all in phase - obviously at the same frequency. The most likely culprit is your metering device needs calibration.

Wow can be far finer than can be measured with a strobe disc. If you can see wow on a strobe disc it will sound really bad.

Since we can be pretty certain your 60 Hz really is 60 Hz, you could have a slightly small motor pulley (if the table uses a synchronous motor) or if it uses a variable speed DC motor, the regulator is a little off.

I worked on turn tables may years ago and can tell you nearly everyone complained of _slghtly_ slow but nobody complained it it was a percent or more fast.

G²

 

[JoeDJ]

I used just a "Kill A watt"

BTW, assuming that the TT uses line hz to lock in motor speed, if you then read the speed with a light bulb with the same hz error, wouldn't the speed still indicate correct?
Correct me if I'm wrong .

In any event it was just the belt lightly rubbing on the guide that caused the slight slowdown .
I'm now happy with the speed. I'm actually surprised how stable it is.

 

[AndrewT]

Unless you're running your own generator, it is NOT 59.9 Hz. To be on the power grid, the generators are all in phase - obviously at the same frequency. The most likely culprit is your metering device needs calibration.

Wow can be far finer than can be measured with a strobe disc. If you can see wow on a strobe disc it will sound really bad.

Since we can be pretty certain your 60 Hz really is 60 Hz, you could have a slightly small motor pulley (if the table uses a synchronous motor) or if it uses a variable speed DC motor, the regulator is a little off.

I worked on turn tables may years ago and can tell you nearly everyone complained of _slghtly_ slow but nobody complained it it was a percent or more fast.

G²

You are wrong.
The mains frequency varies each time the load changes.
The load changes all the time.
Therefore the frequency changes all the time.

 

[stratus46]

I used just a "Kill A watt"

BTW, assuming that the TT uses line hz to lock in motor speed, if you then read the speed with a light bulb with the same hz error, wouldn't the speed still indicate correct?
Correct me if I'm wrong .

In any event it was just the belt lightly rubbing on the guide that caused the slight slowdown .
I'm now happy with the speed. I'm actually surprised how stable it is.

You're correct. Using a line timed strobe like a neon bulb would read the same as the line frequency changed which was why I mentioned DC dervos.

G²

 

[Mark Kelly]

Image courtesy of Leapsecond.com

 

[Pyramid]

Turntable speed measurement

There seems to be a lot of lively discussion on this site regarding turntable speed and stability. I became interested when designing a digital PSU to control the platter speed and was confronted with the problem of measurement: Stobes are only slow/fast indicators and somewhat awkward to use and handheld tachs are too inaccurate and subject to movement. I eventually built a digital tach with 0.001RPM resolution.

I soon discovered that most of the PSU's out there were too coarse (0.1RPM steps) to dial in the speed of the platter. The PSU I was working on had 0.01RPM steps which was better, but the next thing I noticed was no matter how close I initially dialed in the speed, it would slowly drift upwards (~0.25 RPM) over a 30-45 minute interval. Since the tach has a serial output, I connected the two together, and the platter now stays within ±0.005RPM, no matter how long it runs.

 

[ticktock]

as I remember it, a tiny bit slower speed gives better timing, rythm, and 'sonics'

or ... maybe its really the opposite
just a tiny bit too fast, and all the good musical stuff is gone

and I believe that is a main problem with all modern music 'reproduction'
but with new and better digital technology this may be changing soon

Interesting theory.

This must be the reason why all Regas run slightly too fast.

Best IMO to playback at the proper speed, obviously if the cutting lathe was running off speed all bets are off unless you have some range of adjustment and know by pitch whether you are on speed or not.

I don't buy that playing off speed is going to be an improvement, but small errors are probably undetectable in practice.
...

agree

 

[JoeDJ]

Actually, it hsa been my experience that slightly too slow is more notice noticeable than slightly too fast.

Slightly too fast can often just make something seem just a bit more lively somehow but, slightly too slow can really get your
attention in some songs as the music seems to "drag" somehow .

 

[tinitus]

when I said 'slow', it sounds like being misunderstood

'slowish' means 'inaudible'
it should not be heard as 'slow'
but its where the music begins to breathe, and sound 'airy and liguid''

and in the same manner, 'faster' should not be audible as being too fast either
it does give the music imaginary pace
but its faking, and not real
'musicality' disappears
it will sound more like a lifeless drum machine

but it may be difficult to hear at all
it's a bit like a live band where the drummer keeps speeding up the beat, and pushes the whole band to play too fast

will the audience hear it
I don't think so
even many musicans won't know the difference
it's a really difficult thing

a small thing, but exstremely important
could be like night and day

and the producer ... who knows what he will do ?

 

[sq225917]

Pyramid, ever thought about making that available commercially?