What's an excellent spec for TT Motor Speed Variation?

[Barry]

IMHO there's certainly a dearth of info on technical specs for turntables. With a Phoenix Engineering tachometer and Eagle motor controller, I measure my old VPI HW-III with Stand Alone Motor Assembly (SAMA) at between 33.333 and 33.337 RPM. How does that compare with today's more modern tables? Yours?

Has anyone seen any specs/studies on this? I'm about to replace my TT with something considerably more expensive. Although I know other factors contribute to TT sound quality, what irony if my new $$$$ one has even less speed stability. Only the new Monaco Grand Prix Audio tables seem to even mention these specs.

[JCOConnell]

This brings up the question, how much motor speed variation is audible?

[Rob]

by the numbers, a belt drive cant touch a DD. that said my two main tables are belt driven and one uses a phoenix eagle/road runner and i'm seeing the same numbers Barry is getting.

[Barry]

by the numbers, a belt drive cant touch a DD. that said my two main tables are belt driven and one uses a phoenix eagle/road runner and i'm seeing the same numbers Barry is getting.

Did you check to see what speed variation was before you added the Eagle? (I didn't).

[Rob]

Did you check to see what speed variation was before you added the Eagle? (I didn't).

I use the phoenix controller on an HW19 MKIV with a SAMA and TNT V platter. the pulley was changed along the way and the upgraded platter was ever so slightly larger in dia than the one before. throw in belt stretch, etc. w/o the eagle it was off about 2% (fast) measured with the roadrunner.

[JCOConnell]

a larger diameter platter in a belt drive system would run slower all else being equal.

[MylesBAstor]

Have you tried this?

http://PlatterSpeed - Vinyl Tool by ProgTec GmbH https://itunes.apple.com/us/app/platterspeed-vinyl-tool/id415629169?mt=8

Here is the useable URL: https://itunes.apple.com/us/app/plat...415629169?mt=8

[jonathanb]

I used Platter Speed before I got the Phoenix tachometer. The app proved quite inaccurate compared to the tachometer.

[Barry]

There's a recent and very interesting discussion on this topic over at diyAudio. As expected, nothing is as simple as it seems. There are some very intriguing embedded references that talk about audibility of speed variability in tape transports and another on subjective research done by the BBC back in 1955. Also included is a link to a Tacet-Vinyl Check test record at Acoustic Sounds. All looks like a few hours of careful reading....

The first line is the link not the second.

[astrotoy]

I use the Monarch PT99 tachometer to measure the speed of my belt driven VPI Classic 3 with SDS. I can maintain speed stability to +-.001 or 2 during the play of a record, that is 33.332 to 33.334. The speed will drift slowly over the day as the temperature of the room heats or cools, but I just check the speed and get to back to as close to 33.333 as I can, within .002 of the correct speed. Again, the variation is .001 or .002 during the play of the record. Never had a DD turntable to compare. Nice not to have to remove the record I am playing to measure the speed. (using the reflective tape that comes with the tachometer..)

Larry

[Rob]

do you have your Monarch mounted on a tripod or in a fixture? I had the digisrobo, which like the Monarch is a laser tach it also read off as strip of reflective tape. what i disliked about it was using the momentary switch to read speed. you had to depress and hold it without disturbing the positioning of the device or you'd get misreads. It could be modified w/ an on/off switch but still have the dilemma of where to mount the device. which meant more apparatus and 'stuff' in the way of me using the TT

[astrotoy]

I hold mine against the plinth of the Classic 3. Holds quite steady for me. Haven't had any issues with misreads. Of course, I gave up caffeine many years ago. Larry

[Guest]

IMHO there's certainly a dearth of info on technical specs for turntables. With a Phoenix Engineering tachometer and Eagle motor controller, I measure my old VPI HW-III with Stand Alone Motor Assembly (SAMA) at between 33.333 and 33.337 RPM. How does that compare with today's more modern tables? Yours?

Has anyone seen any specs/studies on this? I'm about to replace my TT with something considerably more expensive. Although I know other factors contribute to TT sound quality, what irony if my new $$$$ one has even less speed stability. Only the new Monaco Grand Prix Audio tables seem to even mention these specs.

Most manufacturers don't give specs much less talk about how their drive systems achieve them; a few do. Some quote clock crystal frequency accuracy instead of measuring actual platter speed. I suspect most don't have the tools for measurement. For the longest time we've taken manufacturer assurances of speed accuracy and stability, comforted by digital read-outs on 'table consoles.

To your question: What's an excellent spec for TT motor speed variation? My understanding is the specification to consider is peak deviation from perfect for measured platter speed. Typically that would be given as a percentage. Ask the manufacturer of the a 'table you're considering for that information. It's important to know how finely resolved are the measurement tools - how far to the right of the decimal point can they go. How often is a measurement taken?

A revolution is roughly 1.8 seconds. If a tachometer sees a piece of reflective tape stuck on the platter, it is taking a measurement once every ~1.8 seconds. I wonder if the width of the tape influences the measurement; I wonder what is being read.

Then there is the topic of what the drive system knows about platter speed and what, if anything, is done with that information. What is the frequency of response.

I spoke with Alvin Lloyd about some of these topics when covering the Monaco 2 turntable (AN link here.) Speed tests using test records (typically a 3150Hz tone) at very best measure the lathe the test record was made on. He considered tools such as the Feickert Platterspeed as toys, though he didn't use that word. They are fun to play with and easy to use. I am not an engineer but I am skeptical there are tools available to the typical hyper finicky vinylist that yield high accuracy about platter speed.

[Rob]

Tim have you used the Phoenix Roadrunner? it uses a Hall sensor not unlike those found in many of the coveted japanese DD 'tables from the '70s onward.

Hi Rob - i'm aware of the Roadrunner and Hall sensors, but have not used the RR. Vaguely recalling Phoenix Egr no longer making them?

[Rob]

Bill Carlin is around, and the Pheonix has risen from the ashes if you know where to find him

[GaryB]

What's interesting to me is that the different methods of measuring turntable speed are telling us different things about the record playing process.

Techniques like the Phoenix Roadrunner or a Tachometer attach a reference point to the platter, either a magnet in the case of the Roadrunner or a piece of reflective tape in the case of a Tachometer. One then measures the speed by checking the platter once per revolution. This is a good indicator of long term speed stability but doesn't give any information about short term speed variation within a given platter revolution.

The Platterspeed app plays a 3150hz tone on a test record and shows one how the speed varies as the record plays. Of course the accuracy of this method depends upon how well the test record was recorded and I've read but not tested myself that the Ultimate Analogue Test LP is better than the Feickert test record. But one shouldn't use test records to check absolute speed - a Roadrunner or Tachometer or a strobe disk is better for that. But the test records provide information on speed variation as a record is playing, which is unique.

Mike Fremer's site provides this data for the turntables that he tests. For example, see the recent review of the Technics SL-1200G https://www.analogplanet.com/content...200g-turntable . He presents data from Platterspeed which shows that the speed varies +.27% -.22%. Barry's first post in this thread shows typical long term speed stability measurements of 33.335 +-0.002 = +- .006%. So it's clear that stability of a tone on a real record is much worse than the long term stability of the spinning platter.
The diyaudio thread that Barry posted (http://www.diyaudio.com/forums/analo...-stabilty.html ) presented a technique for plotting the Platterspeed data in a way that is more intuitive and easier to understand. It takes the data and converts it into a polar plot showing speed variation within a single revolution. One can see speed variation due to things like record eccentricity, platter imbalance, bearing noise, and tonearm/cartridge resonance. All of these things lead to speed variation even with a perfect motor.

Turntables really are complicated and even a simple question about what's a good spec for speed variation isn't easy to answer.
---Gary

[GaryB]

Not really the same problem. One is variance of the mean and the other is variance around the mean. It's an important distinction because the solutions to these phenomena are quite different.

Okay, I think I get it. You're discussing something different than the OP's question. Imo before introducing multiple variables that cause that question to become almost unanswerable it's relatively easy to start with peak deviation of the platter from 33-1/3. Of course that's not the sole factor for choosing a 'table, but it's a spec that does not lead us down the road to responding "there is no good answer because things get so complex" and 'table comparison, at least on paper becomes fruitless and frustrating.

[GaryB]

Tim - I understand your point but it's feels like it's moving close to the thought that we should compare amplifiers by measuring thd (total harmonic distortion) because it's simple. But does it really correlate with good sound? Direct drive turntables can get speed almost perfect but only a few of them actually sound good. I agree that's not the original poster's question, but it is perhaps more relevant.

[Guest]

GaryB commented
08-21-2017, 04:21 PM

Tim - I understand your point but it's feels like it's moving close to the thought that we should compare amplifiers by measuring thd (total harmonic distortion) because it's simple. But does it really correlate with good sound? Direct drive turntables can get speed almost perfect but only a few of them actually sound good. I agree that's not the original poster's question, but it is perhaps more relevant.

There seems to be a greater lack of manufacturer information about turntables than most amplification and speaker components. I'm not worried that by supplying more information manufacturers will cause anyone to think there is a solitary specification for gauging turntables.

Imo, supplying some reasonably standardized turntable specs is a good thing. I'm not talking about tonearms or cartridges or records, just turntables. Of course all those factor in to a sonic assessment of some specification combination of them, but I think we can talk about what are the characteristics of a well performing turntable - a well performing turntable being one likely to yield a high sonic evaluation - without having to talk about ancillaries. We certainly can discuss, say, general characteristics of well performing tonearms, without necessarily talking about what they are mounted on.

The absence of specifications encourages the notion that its all so complex. I've been reading a lot of turntable threads lately and a common theme appears where many people don't want to talk about performance specifications - often because they don't have them - and in the face of 'tables that do have them frequently say "there's so many factors to consider that we can't rely on just one." That's a misdirection or non-sequitar, imo. Not trying to diss anyone, its just what I've encountered.

I'll agree with you that not all examples of any particular drive topology correlate to good sound.

Independent of drive topology I'll say the two most important factors for a well performing turntable to possess are: 1) stable accuracy and 2) low noise. Turntable buyers should look for that information from manufacturers and ask how are the numbers obtained. (A corollary inquiry being, are there factors that lead to losing accuracy or gaining noise over time, eg. belt or bearing wear, oil changes, etc.) That's where I'm at today and I'm willing to change my view if more relevant factors are discovered or a convincing case is made otherwise. Now it doesn't follow that all 'tables possessing those characteristics will sound good but having them would not be the reason why.

Thus its not surprising that someone who takes a similar view will want to know what is an excellent specification for TT motor speed variation and which 'tables meet that specification. And that will not be confusing to them or lead to thinking those are the only factors to consider when considering what to buy. I think Barry asked an excellent question.

Nowadays on other forums I read of more turntable buying decisions based on looks more than anything else. Beautiful wood plinths or bright metal bling can get their foot in the door quicker than a wow or flutter spec. :-)

[JCOConnell]

I think the pursuit of perfect speed and zero wow and flutter may be overrated. Ive been running my Aries-1 off straight wall power for a couple years now since my SDS died and haven't noticed any degradation in sound quality whatsoever. Ive either got great AC, or I'm not that sensitive to minor variations in speed.

[EdAInWestOC]

I use the Turntabulator app to fine tune my VPI ADS monthly. You start the app, place the phone on the platter and start the platter spinning. It will periodically re-sample the speed, which allows you to adjust the ADS fine speed controls. It is very handy.

[david k]

I use the Turntabulator app to fine tune my VPI ADS monthly. You start the app, place the phone on the platter and start the platter spinning. It will periodically re-sample the speed, which allows you to adjust the ADS fine speed controls. It is very handy.

I haven't found Phones totally accurate or reliable enough as measuring devices just will do in a pinch good, did you compare the results to a quality strobe Ed?

david