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Turntable speed analysis part II

I don't really care much about the yamaha, it just happened to be the cheapest semi decent turntable I could find when I moved to the USA and left all my hi-fi in the UK.

Its interesting the cogging is pronounced twice per prevolution in the same spot with the same amplitude.

I hope to have my diy turntable hooked up to the pc soon. I dont expect it will be pretty.
 
FWIW I've performed some eddy current brake experiments on my LP12 Lingo. At the levels of drag I was using there was no extra problem. The pictures don't look great compared to John's, either I have an inherently bad motor or the turntable needs some general work. Maybe the belt is upside down.

Here's the 45-55Hz spectrum, taken at 96000Hz sampling which adds further confusion,

LP12_cmp_45_55.png


The peak drops significantly, and the little sidebands at the base of the peak vanish.

Paul
 
Hmm..interesting; the graphs would suggest an improvement. I might do mine again as the suspension has been altered and this may well produce a different result than achieved previously (if that's OK with you Paul?).
 
great thread still guys....

out of interest does anybody know of an engineer who could fabricate or modify a bearing for me? i was wondering about dom from northwest analogue (is that correct?).....

i would like to get my othello working again.....it's such a pretty record deck!!!
 
sq225917 said:
That's a decent reading for a standard (motor wise) LP12
Click to expand...

I would expect it to be about as good as you can get with a Mk I Lingo as the deck had a brand new Cirkus bearing, springs and belt and had just been serviced. The Ultimate Analogue test record was also brand new and the recording came off the second play (first one was to calibrate the recording).
 
Here is the same 3150hz track played at 45rpm. It was actually recorded at 24/96 and down sampled, hopefully that does not make any difference. A quick look at the spectrum also shows it is running slightly fast at 45rpm, I might have a go at tweaking that tonight.
 
If I recall correctly Rega turntables used the same Airpax motor as the LP12 in the past, could this be the improved motor we are looking for? The blurb certainly sounds promising and the cost is very reasonable.

24v-upgrade-full-kit-image-.gif
 
John's LP12 at 45rpm,

Spectrum,

JohnCLP12__45_0_20.png


Polar,

JohnCLP12__45_polar.png


I don't understand why the polar looks nicer where the low end spectrum looks worse. It's possible the filtering bandwidths that get used need reviewing.

The money shot,

JohnCLP12__45_45_55.png


This shows that the 50Hz peak in the spectrum is motor drive frequency related.

The slightly confusing shot,

JohnCLP12_62_72.png


The 45rpm drive at 67Hz is shown, but it's nothing like as striking as the 50Hz.

The turntable is running the same proportion fast of 45 as it is of 33.3, which implies the drag remains effectively constant with speed. So that's useful to know. It therefore seems likely that either the motor runs more smoothly at higher rpm or the belt/platter inertia resonance is a little high. A stretchier belt would be an interesting experiment.

(FWIW the spectra of the recordings show significant 50Hz breakthrough, and the 45 also has a 67Hz peak, which implies the earthing/shielding/etc arrangements might be improveable.)

Paul
 
I'm not sure which motor the Neuman VMS80 lathe uses but artefacts from it don't appear to be an issue with the Ultimate Analogue test record. I see Stamford Audio do it for £40. Is there anywhere that does it for less?

Out of interest has anyone tried the re-made HFN test record?
 
I think a significant part of the regular waviness, and there is one lap that deviates (bottom right on John's plots) are embedded in the record. But it's probably as good as we can get.

When I looked the HFN record didn't have a suitable tone.

Paul
 
I found it interesting that on the demodulated spectrum there was very little trace of the 67hz, When i demodulated it, I assumed I had done something wrong.

The 67hz signal is very plainly evident on the spectrum of the 3150hz recording however.

On the spectrum for the 33.3 rpm recording, there are a bunch of other artifacts not present at 45rpm, a peak around 730hz, 250hz, and 150hz, perhaps these contributed to the 50hz spike on the demodulated spectrum.
 
Paul R said:
The turntable is running the same proportion fast of 45 as it is of 33.3, which implies the drag remains effectively constant with speed. So that's useful to know. It therefore seems likely that either the motor runs more smoothly at higher rpm or the belt/platter inertia resonance is a little high. A stretchier belt would be an interesting experiment.
Click to expand...

Yes, I noticed that as well. I adjusted the angle of the motor very slightly as recommended in the LP12 set up manual, but it did not make much difference.

(FWIW the spectra of the recordings show significant 50Hz breakthrough, and the 45 also has a 67Hz peak, which implies the earthing/shielding/etc arrangements might be improveable.)
Click to expand...

The set up to allow me to connect to the computer is not ideal, I guess this could be noise introduced somewhere outside the record deck?
 
pure sound said:
I'm not sure which motor the Neuman VMS80 lathe uses but artefacts from it don't appear to be an issue with the Ultimate Analogue test record. I see Stamford Audio do it for £40. Is there anywhere that does it for less?
Click to expand...

I don't think so, I paid about £42 for my copy including postage. I am happy to loan it out if you slip a fiver in the envelope when you return it - just PM me with your address.
 
I got mine from one of the shows, mispriced, at a tenner! Happy to post to post to anyone who wanted to try it.
 
I'd be interested in borrowing it Simon. I'll redo recordings from the SP10 as well as the Voyd but it'd also be handy for looking at the RIAA correction my new phono stage is applying.
 
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