Turntable Speed Analysis Tool

[nat8808]

Well, one would really have to do the measurements with and without the bearing to be able to draw any conclusions.

Amen to that! Too often people assume their 'upgrade' is a great improvement without comparing to the previous state. Maybe it was good all along.

Be good to test my Anni, I'll have to check out the thread.

As a related aside, someone on vinylengine tested his 3 Pink Triangle Anni decks (one DIY, one original, one upgraded by Funk Firm) by simply recording the same track on each. Some resonances inherent in the working of the deck were apparent simply by looking at the audio - the resonances seemed not to be there in the vector'd deck with current feedback PSU K-Drive (compared to the two using servo feedback). Can't discount differences in set-up but still gave a clue to something, whatever it was!

Thinking out loud, could those records with Time Code on be used for a similar thing? They're used as a way of controlling software via a real record deck, e.g. for DJ-ing MP3s http://www.thedjshop.co.uk/digital-d...ime-code-vinyl

[MartinT]

Too often people assume their 'upgrade' is a great improvement without comparing to the previous state.

Umm, well there's the little matter of it sounding hugely better than before. I didn't need a measurement to establish that.

[nat8808]

Umm, well there's the little matter of it sounding hugely better than before. I didn't need a measurement to establish that.

Perhaps the bolts were previously loose from years of use and putting in the new bearing meant everything was tightened up properly again?

I'm only speaking generally, not implying that Mike's bearings aren't an improvement.

There are too many variables to say that changing it was an improvement without going back and changing it back with only that one variable, even if tested by ear.

[MartinT]

Perhaps the bolts were previously loose from years of use and putting in the new bearing meant everything was tightened up properly again?

There was nothing wrong with the bolts. An inspection of the two bearings quickly demonstrates the massive difference in engineering standards. The sonic differences are not small.

[nat8808]

There was nothing wrong with the bolts. An inspection of the two bearings quickly demonstrates the massive difference in engineering standards. The sonic differences are not small.

Might well sound different to you but the one measurement afterwards is meaningless.

"....yeah, but this one goes up to 11".

That you find it sound better is obviously the important point. Just don't bother with the test unless you just want a certificate for its current measurement.

[MartinT]

Just don't bother with the test unless you just want a certificate for its current measurement.

I have an engineering mind and am capable of correlating some measurements with what I hear. Seeing the test results is always interesting, but the listening is all the proof I need. No certificate needed here, we're talking about an appreciation of music after all.

[Macca]

Might well sound different to you but the one measurement afterwards is meaningless.

"....yeah, but this one goes up to 11".

That you find it sound better is obviously the important point. Just don't bother with the test unless you just want a certificate for its current measurement.

Nat - the idea is to compare the modded Technics speed stability to other decks - not to the un-modded techie - although a comparison would be interesting.

[Mike_New]

We are after all, only trying to measure the parameters and qualities of a simple rotating surface.
There is only one way to definitively measure rotational accuracy and consistency and that is by using a qualified angular diffraction grating. These are used to certify the accuracy of angular and rotational encoders used in practically every application from high precision machine tools and robots, to satellite dish’s. Indeed diffraction gratings themselves are used in high precision units.

For any meaningful measurement based on a test standard, then the known and measured accuracy of that standard must be at least an order of accuracy higher than the predicted accuracy of the measurements we are trying to make, otherwise the result are meaningless.
If test records do have anomalies, then what are we looking at when we a
review the impressive plots and data produced my the resulting mathematical analysis??

I doubt if any test disk, or the lathes which cut the masters, are calibrated in this way.
indeed I doubt if they need to be!!

When we get the results, what happens next week when the mains voltage drops by 10V
or we switch on the aircon.??

The most reliable and meaningful long term approach to asessing the accuracy of your TT, would be to use one of the laser strobe devices I mentioned earlier.

Maybe Marco or Martin could buy one of these devices and rent it out to those who would like to use it.

[Lodgesound]

A cutting lathe has a servo system fed with a once-round pulse generator along with a diffraction-grating based frequency generator feedback loop.

The master servo reference would be from an outboard sync. pulse generator with an accuracy of around 6 decimal places to it's master reference frequency.

These facilities sound almost insane but are completely standard in a professional installation and ensure an extremely high standard of operational stability that massively exceeds systems in most domestic situations.

Masters made on such lathes are obviously to an exceptionally high standard - most home turntables have rotational errors which you will as a listener never hear or even be aware of in a million years unless a fault develops with your turntables. Technics SL1200 series are extremely stable as are many belt drives.

The biggest problem by far and one that causes severe rotational stability issues is the hole in your record NOT being precisely central relative to the grooves. Even a very slight error here will utterly trounce any performance of the platter itself.

Some professional designs I came across had the ability to offset the centre spindle and had a runout meaurement on the end of the tomearm to minimise this each time a disc was loaded.

It never ceased to amaze me that such a facility was never made available even on turntables costong £10 000 or more.

Eccenticity is the biggest bugbear of playing analogue discs as regards speed stability.

[YNWaN]

Mike, perhaps you are unaware as to how wow and flutter figures for turntables are normally measured? If you look on YouTube you can see the strobe you describe being used - they show some interesting results - but not the kind of results that Paul's technique gives. I'm not sure why you want to decry this measurement procedure - it is, essentially, a higher resolution version of a recognised process.
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Stewart, Nakamichi made a turntable that measured the eccentricity of a record and automatically adjusted the position of the record to correct it. It is also possible to do a similar thing (although manually) on Roksan's decks (as the record spindle is removable).