Turntable Speed

Modern direct drives and many belt drives have this feature. That is to adjust speed. May be an integrated strobe or checking with any kind of strobe disc. For the remaining belt driven ones you pray for belts within specs.
Not having a window for checking revolutions mostly a design approach.

petg60, thank you for the primer!

This is quite a good app for iPhone and Android to check your turntable speed. Simply lay your smartphone on the platter. Start the turntable and get a reading:

https://play.google.com/store/apps/details?id=com.apkossa.rpmeter&hl=en_IE&gl=US

tkr -- If you're sensitive about such things, what happens when you test your turntable and it comes up with the wrong speed? Ship it back?Demand another one? And what's the chance of that next sample being right on?

Have another glass of wine and you'll be less sensitive.

tgyeti. there is a strobe pattern on the bottom of your platter and you are seeing it through a prism. Older turntable drive systems could wander a little so having a built in strobe was handy. Some people also like being able to match pitch. Modern turntables tend to avoid strobes either because of the added expense or their advanced drive systems are always locked in to the exact speed. Some modern tables display the speed electronically by reading a magnet or light strip on the bottom of the platter. The most advanced systems read the platter then maintain exact speed regardless of the drag exerted on the platter. 

tkr 

Is a phone safe on a turntable doing 78 rpm?  😊

Tried the app. I get 33.39-33.41 on my Pioneer PL-630.

ibmjunkman -- Thirty-three-and-a-fourth. Scandalous!

@edcyn:

If the speed is way off, you should maybe buy another turntable with speed adjustment possibility. 

@ibjunkman:

I have never tried it on 78. Your iPhone would probably stay unharmed and on the platter if you laid it close to the center of the platter.

I really don´t understand your objection- would you rather not know if your turntable speed is way off?
The RPM app is just a simple and reliable way of knowing if your turntable operates at the right speed.
What could possibly be wrong with that? IMO it´s a basic parameter when playing vinyl.

If the speed is off then the pitch will be wrong. Especially noticeable on piano. Generally there are speed adjustments on motors, usually screws on the plinth under the platter. Sometimes you will see colored paint on the screws to mark their settings. They adjust the tilt of the motor and how the belt rides on the pulley which can adjust the speed. This along with a new oem belt and proper lubrication will usually correct speed problems. 

Those iPhone apps for platter speed are notoriously inaccurate at the level audiophiles want them to be accurate. What you get is the false satisfaction that you’ve seen a digital readout on the screen. I would recommend the KAB strobe system instead. Uses a large diameter strobe disc and a battery powered strobe light for constant frequency. But you don’t get a digital readout. Strobes built into turntables and any plug-in strobe light are subject to variations in AC line frequency.

@lewm, I have "RPM" on my phone and it seems pretty accurate. The Cosmos I have coming (hopefully soon) has a digital rev counter which I will compare to the phone. I made a hockey puck sized one inch thick platform with a center hole. It is placed over the spindle creating a dead center platform for the phone. It is made out of alder and is sized to match the weight of a 180 gm record. The phone is centered over the spindle. The phone also gives you wow and flutter. When it starts increasing it is time for a new belt.

The operative word is "pretty", as in "pretty accurate".  Most of us are looking for speed errors or more importantly speed variation of less than 0.1 RPM against a background of 33.XX RPM.  I am mostly basing my claim on reports of others who first monitored speed with a cell phone and then used other more accurate methods, e.g. the Sutherland Timeline or the Phoenix Engineering Roadrunner or even the KAB, and found that the cell phone app in question was off a bit.  I don't think absolute exact 33.333 rpm is a necessary goal. I do think that keeping speed constant within a very small bandwidth is much more important, as we are much more sensitive to warble than to absolute pitch.  For starters, the cell phone itself does not match the actual load of an LP being dragged by the stylus, neither in weight nor in distribution of mass.

Turntable speed for me needs to be accurate enough to tune and play a guitar to.  If the band is playing in "E", I want to be able to tune my guitar (using a tuning fork) and solo along to that (given a modern recording where the band had the right pitch in the first place.)   My KAB strobe gets me there, although I acknowledge it's not 100% accurate.

Only product I know that's VERY accurate is the Timeline device. Don't know if it's still made.
https://youtu.be/RF2XieUlzvk

Timeline itself is accurate. The problem with it is that it relies on a human being to assess its accuracy by following a laser dot on a wall. Probably the timeline is better than the observers of the timeline.

I have a mint condition Yamaha P-550 turntable that I bought new in 1983 that also has the strobe light adjustment.  I had it completely serviced to set up a turntable system for my youngest son a couple of years ago, and it dials in the speed like butter now.  Very nice, low maintenance, budget turntable.

Second the KAB strobe disc. 

The SOTA Eclipse package with Condor and Roadrunner is a very worthwhile upgrade for a belt drive turntable that you are invested in that doesn’t have automatic speed correction. I did the upgrade on my VPI Classic 4 myself. Combined with an Origin Live belt it totally transformed the sound. W/F is .06 as measured with Analog Magic and speed consistency as shown by the Roadrunner usually shows 33.333 + .001 or .002.

I use the Phoenix Engineering Eagle and Roadrunner to control the motor on my Lenco.  PE designed the Eclipse system for SOTA and certainly it is wonderful for any turntable with an AC synchronous motor, but now we are talking nearly $1000 in cost.  (SOTA includes a proper motor in the total cost of the Eclipse, which does ease the pain a bit.)  For comparison, KAB strobe kit that includes a wide diameter disc and a battery powered strobe light is about $100 and won't correct platter speed; it just tells you where you are.  The Sutherland Timeline is about $400 and not worth 4X the cost of the KAB kit, IMO.  If I owned a vintage DD turntable (whoops, turns out I own 4 of them), I would check speed even if the built-in strobe suggests it is spot on.  I am not so sure that those built-in devices are sensitive to speed variation due to stylus drag, etc, or slight errors in set speed.