@richardkrebs-
ThinGap does make a different series motor (LS51, same price ~$600 in qty.) with higher pole count (higher driving freq), lower power (48W) and higher winding resistance (4Ω); it is still coreless and would be much better suited for a DD table application the the TG23x series and could be driven from a class AB amp. It’s been available for a couple of years, so I’m not sure why it didn’t get used in this case?
The HW40 gets great press because it does sound good and even measures respectably, but no where near the numbers VPI claims for W&F, speed accuracy or torque. Of all the reviews I’ve read, I don’t believe I saw a single measurement; making matters even more difficult, you need the software from Elmo (you can it download free from their website) and need to construct a serial cable to connect a PC to the controller in order to get some of the relevant measurements. Luckily, the parts are readily available thru Digikey. With the software, you can also do 78 RPM or adjust the tempo for off speed records such as the Stones Beggar's Banquet, in steps of ~0.07%.
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Hi phoenixengr. VPI have made interesting choices in the controller and motor. You would think that Thingap would make a motor with low speed/power windings ( higher resistance ) making for finer speed control from the Elmo. All that said, the TT gets great press, so the package seems to work very well indeed. |
@lewm too modest. That should be clear to anyone (wherever their vested interests may lie).
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The point I tried to make earlier and which seems to have been ignored by some who might favor turntables with laissez-faire speed control is that yes, live human musicians will inevitably vary tempo during the course of a performance of a given piece of music and given conductors will pace different classical pieces differently, but that's the crux of the matter. You/I want the turntable to make no alterations of tempo that might obscure the human factor inherent to the pleasure of listening. The turntable should ideally do no editorializing, in other words. Plus there is the fact that inconstancy of turntable speed affects pitch, whereas human errors in timing produce only changes in tempo. No turntable or drive system is absolutely perfect in this respect, but that should be the goal. In my opinion, of course.
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Anyway, who do you send the masters to for pressing? @mijostyn I've found that if the mastering is done correctly most pressing plants can do a pretty good job. But QRP stands out as the best (their pressings have noise floors that easily rival Redbook), RTI is excellent and oddly enough we've had very good results from United. One of our projects was pressed in Holland, not sure which plant but all the US plants were 3-6 months behind at the time. |
Unfortunately, I haven’t had the chance to "look under the hood" on very many of them, but based on my limited exposure:
Belt drive: American Sounds AS2000. David Karmeli not only understands high end audio, he gets the physics and engineering part right as well. His design philosophy may be unique in the industry. Full disclosure: I had a hand in designing the motor control for this table, based on the Eagle PSU and RR tach.
Direct Drive: I’ve not auditioned the new Technics tables and I don’t have a lot of technical info on them, but from what I can gather, they are doing some really sophisticated things in motor control and they have the engineering HP to do things right. It wouldn’t surprise me at all if they were doing FOC.
I’m basing my observations more on an engineering perspective than an audiophile one. YMMV.
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No kidding. Just for the record phoenix what turntable manufacturers drives do you like the best and why? |
I am getting a sneaky sensation that phoenixengr
just might know a thing or two about TT motors.
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"....why do you think VPI use trapezoidal commutation?
Surely this is not optimum if they want to minimize torque ripple." The controller is made by Elmo Motion Control (Gold Twitter Solo), and while Elmo's PC control software is fairly comprehensive, I'm not sure if the controller is capable of sinewave drive; it is not capable of sensorless operation (FOC) which would use sinewaves. Sinewave drive is considerably more complicated and would result in smoother operation, but for whatever reason, VPI chose to operate the motor in the simplest mode available, as a DC motor which uses block commutation and Hall sensors. They do some other rather strange things: The motor is designed for high power (500W) so the windings are 0.3R; not the easiest load to drive especially from a class AB output amp. The Elmo controller uses PWM output at 10kHz, which IMHO is a bad choice for use around a sensitive audio circuit like a cartridge pickup (especially MM). |
Hi phoenixengr. why do you think VPI use trapezoidal commutation? Surely this is not optimum if they want to minimize torque ripple. Cheers |
Thx Phoenix
Great post which actually makes sense to myself. I must admit some prior posts have shot right over my head but now I am trying to think in industrial terms which is something I am at least vaguely familiar with.
We rotate, amongst other things, 900 to 1200lb steel rollers with a required very high degree of speed accuracy precision.
Think in terms of 3 phase 5 to 25hp motors for this task.
Current feedback has proven very effective at precise control AND eliminating the pesky noise problem sometimes seen on 0-10vdc and 4-20ma control feedback circuits.
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"In my industrial world, traditional motor absolute speed control was obtained by either servo motors/ controllers or motors with speed encoder feedback.
However in past few years drive controllers have become so sophisticated that now best speed regulation is obtained by running " open loop" with zero encoder feedback and using current feedback at the controller itself.
Now is this a possibility for TT speed control or is this how some are already controlled?" It depends on the type of table. For belt drive (the LFT1 is BD), the motors are relatively high speed (300/600 RPM) with low inertia rotors so open loop speed control is possible. The SOTA Eclipse package does this with a BLDC motor run as a 3 phase AC synch motor and the motor speed is very stable and accurate. The RR tach is used to counter long term speed drift as the table warms up. Running a direct drive motor open loop is much more difficult because of the slow speed and high inertia of the platter. With no feedback, the platter speed will wobble considerably. Most of the DD tables that I’ve seen use a rotary encoder for speed feedback and a DC servo control to drive the motor. The VPI HW40 uses a magnetic ring encoder and drives the BLDC motor as a DC type using block (trapezoidal) communtation and Hall sensors. Because of the LPF in the feedback loop, the platter speed is still susceptible to oscillations, although with a heavy platter, it will move the oscillations lower in the audio band vs the light platter DD tables of the 70’s and 80’s. The HW40 does respond to variable drag on the platter, but it is quite sluggish, slowing down for ~250mS before compensation is applied and takes another 250mS to correct, so it does little to affect W&F. Current feedback is still feedback, but if implemented correctly, it can eliminate both the encoder and the delay in the feedback loop. Field Oriented Control (FOC) monitors the current in the windings and can compute the rotor flux position on a de-rotated frame of reference so the control loop operates at DC. The current control loop regulates the torque of the motor and a speed loop is wrapped around the current control loop (changing torque changes acceleration and therefore speed). The speed feedback comes from an estimator circuit that derives the back EMF signal (rotor speed) without external sensors and works well at low speeds as well as in the presence of high noise. I don’t know of any mfr that uses this method, but it would be interesting to try. |
Non-feedback motor controlIn LFT 1, the rotation control is not performed, and the constant speed rotation is left to the high moment of inertia of the 27 kg platter, creating a rotation free from unnecessary vibration caused by the control. Only the positive direction force is applied from the motor, but by using a coreless motor with less moment of inertia, the influence of the vibration is reduced. Motor rotation control with no negative feedback · The XFD method realizes a drive with the minimum fluctuation.
*XFD method: Based on a crystal oscillator with high frequency precision, a direct digital voltage generator is formed to supply a voltage with high precision without fluctuation. It is a system that was independently developed by CS Port. It is a system that eliminates fluctuation by driving a super heavy platter with light load bearing with a low inertia coreless DC motor.
the above approach is with the CS Port LFT1 turntable http://www.csport.audio/products/products-lft1-en.html |
Just some random thoughts and maybe I missed this.
In my industrial world, traditional motor absolute speed control was obtained by either servo motors/ controllers or motors with speed encoder feedback.
However in past few years drive controllers have become so sophisticated that now best speed regulation is obtained by running " open loop" with zero encoder feedback and using current feedback at the controller itself.
Now is this a possibility for TT speed control or is this how some are already controlled? |
Ralph, I asked that question. It is not easy to master high quality records.
We hear the results which are not always optimal. I was just listening to Kate Bush's "Before The Dawn." The rumble forced me to turn my subwoofers down. It is a common problem with remastered albums. I assume this is from poorly maintained lathes. It is a very rare problem with older pressings. Even rarer in old classical pressings.
Anyway, who do you send the masters to for pressing?
Mike |
Ralph, i was not the 'Mike' asking you that question. i already knew you had a lathe and mastered Lp's. |
Ralph, What are you doing with a lathe? Atma-Sphere going to start making records? @mikelavigne We've been mastering LPs for about 5-6 years. Most of the projects we've done are local. It took some time to refurbish the machine and sort out how to operate it. Fortunately I had some help from Len Horowitz of HRS. |
i have maybe 20+ recordings of Beethoven’s 5th and double that of the 9th.
every one has a slightly different tempo. even by the same conductor and orchestra.
none are really wrong. just different. i do have my favorites.
which is a different issue than tonal solidity verses that very distrating slightly wa-wa sour sound of speed discontinuity. |
Hey Chris
You know that really got me thinking.
You are so right as I now remember listening to live tapes of our band from different nights and yes the tempo was different night to night.
I mastered our "sessions" into a tape I considered good enough to sell at venues and/or send off as a demo tape so always chose the best performance of each song whether they were from the same show or not.
We are human beings not machines so a live performance IS going to differ ever so slightly every time.
And probably true that myself (bass ) and our drummer might have ultimately drove that tempo overall.
And here we are with people worrying about 0.001% speed difference.
Lol.
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uberwaltz
I routinely run my TT,s and my R2R ever so slightly fast deliberately just for that sense of extra attack, drive and dynamics. Hi Kevin I know a guy that actually likes the speed a little slower. Some of my fondest music memories are of listening to music groups/bands in nightclubs on a regular basis, before the whole marriage/kids, and lack of time .... The tempo of the performance was never the same, night after night from same bands. In fact it seemed to me that the tempo for a specific night was set, based on the state of how the drummer showed up. *^) |
Dude, quit while your behind :) |
Mike then we agree, knock yourself out. I'm sure it is a lot of fun for you. I would rather spend my limited money on stuff that would make a substantial difference like ear plugs for my wife:)
Anvil, stylus friction is going to have the same effect regardless of bearing friction. A system with more power and inertia might not be effected as much. How the motor is coupled makes no difference. Pulsating magnetic forces under a very sensitive magnetic device is just asking for it. This is the reason most of us think direct drive tables sound terrible. I am certainly one of those although I am always open to new designs like the Monaco. There is no reason to even go there. Any improvement in speed accuracy over a good belt drive table is inaudible. It is easier to make a silent bearing if you do not have a motor wrapped around it and you do not have to worry at all about stray magnetic fields as the power of a magnetic field drops with the square of the distance.
Guyw3, that would certainly work but is more difficult to set up. Most of us just throw a strobe disc on the record while playing and set the speed while the record is playing.
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Mijostyn , you are looking at it from the wrong angle. Added stylus friction is inevitable but the system can be optimized to best deal with it. Lowest possible bearing friction is part of that puzzle. Low friction bearing make even small motors look huge .A heavy platter helps but rpm ultimately goes back to the motor and how its coupled.
Regarding magnetic forces under a platter or cartridge it is irrelevant if the TT is designed for it. Shielding a magnetic force is easy although not always inexpensive. |
The simplest way to correct for stylus drag is to play a test tone, say 1000 Hz, then adjust the speed of the turntable (if adjustable) until the frequency read-out on a frequency meter reads 1000 Hz. A good Fluke meter with frequency read-out will do nicely. There may be a different drag for different frequencies, but setting it for one frequency seems about the simplest solution. |
OK, enough BS about setting RPM with or without a record being played. Any decent TT has one of several motor-speed control methods to lock-in on or close 33 1/3 (or 45) RPM. Having arrived at "any" RPM setting/value the motor-speed-control compensates for stylus drag or lack thereof. That's why its referred to as speed-control. The Raven exemplifies the precision of its "speed-control" in the video. Because the laser point "changed position" due to stylus drag or lack of is only proof of its existence for that brief interval before compensation is made. If the RPM be exact the point after negative feed back should remain steady which it does. Because it has moved to right or left is not an argument but holding steady under varying loads is testimony to the TT's motor-speed-control's accuracy. The beauty of the Timeline is to allow you to set the Raven's RPM as close to 33 1/3 as possible and doing so with or without drag is BS. Video shows the laser point holds rock steady 33 1/3 RPM under all conditions including no drag. If the point moves with each subsequent revolution of platter it indicates other than a 33 1/3 RPM but says nothing of the TT accuracy of holding a desired higher or lower RPM setting. That's what's important.The timeline is nothing but a clock flashing every 1.8 seconds. Stick your finger on platter and you change laser point position and MSC should keep it steady where ever this dot ends up. Because the dot has changed original position only indicates a sudden load event has occurred. If perfectly set at 33 1/3 and dot is stationary after initial load change dot on wall will remain at position. A movement of dot merely indicates other than non attainable perfect RPM which isn't the most important thing here.
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Very nice looking system Mike!
Those platforms are indeed impressive. |
mike, there is such a thing as "carrying it to far." Why don you just stick your turntable in an isolation camber so airborne vibration doesn’t get to it? I bet if you sit on one of those tables your hearing will improve:) in a thread about ’stylus drag’ you are complaining about ’carrying it too far’? really? i think any participants in this thread would be considered by non audiophiles as ’carrying it too far’. it’s what we do here. i will shamelessly admit to likely being at the far end of the ’carrying it too far’ bell curve. i have 5 of those modified active platforms in my system; under both of my mono block amps, under my preamp, under my dac, and under my turntable. they are awesome tools to eliminate resonance. the musical connection they allow, especially when the music gets very dynamic and soars, is worth it. you can see pictures of those platforms if you look at my system page. 'carrying it to far. i'm the poster boy for that. |
IIRC, Ralph has made a number of records.
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Anvil, any added friction is going to slow any table down a bit unless it has a compensatory mechanism. Most tables create an equilibrium situation which in table like the big Kuzma is probably strong enough to overcome stylus drag. In some tables like the older SOTAs you can adjust the equilibrium with the stylus down but the table itself is not compensating. This is not the case with the new ones. The Monaco is fascinating because it's resolution is so high but it is direct drive and unlike mikelavigna I do not like big magnetic things under my cartridge.
mike, there is such a thing as "carrying it to far." Why don you just stick your turntable in an isolation camber so airborne vibration doesn't get to it? I bet if you sit on one of those tables your hearing will improve:)
Ralph, What are you doing with a lathe? Atma-Sphere going to start making records?
Mike |
Chris
You took the words from my fingers sir!
I routinely run my TT,s and my R2R ever so slightly fast deliberately just for that sense of extra attack, drive and dynamics.
Correct?
No but it's my system and ears and stability is key for me NOT absolute speed being locked at 33.333333 recurring.
Heck if it was good enough for Fleetwood Mac it works for me. |
A key to reducing the effects of stylus drag is reducing turntable bearing friction. Ultimately, the effects of drag all go back to the motor. If it has less work to do overcoming bearing friction so much the better. |
lewm
I THINK that some of us are saying this: Absolute accurate speed is not the issue. I learned how important speed stability was, over the actual speed when I was 10 years old. Got my first - to me - portable stereo - Hitachi am/fm with cassette and microphone. The next few days I filled one tape - recording music from FM. When the tape was full, I played only my tape of music for the next week. I remember to this day thinking what freedom I had to play my own songs. Of course I had taped songs that triggered a "happy mood" in me. Life was good. ************************************ After one week, I switched to, and listened to FM radio again. Something was wrong. I noticed that the songs I had recorded now coming at me through FM, did not sound as good as my taped version. They sounded slow and lethargic. I was confused. My tape version of the songs had a better tempo, more energy. More life. Sometime later ....I figured out what had happened. *********************************** The tape motor in my stereo was running fast. Oh... it was a stable and consistent enough speed, so it sounded ok. It was just running a little fast. I learned at 10 years of age that "Speed Stability" is what is important. Sometimes I like to speed up my turntable, up a bit, you know ....go audiophile crazy.... just to hear older female voices ...........sound younger. Fountain of Youth ? Try that with your digital. |
@phoenixengr From what I've seen, most of the DD tables use a DC motor with servo
control (feedback) to maintain proper speed. This of course, comes with
its own set of problems. Would you kindly lay out what the main problems are? |
back years ago when i switched from my Basis belt driven tt, and belt driven Rockport Sirius II SE, to the direct drive Rockport Sirius III turntable; the most obvious ’stylus drag’ thing i heard was lack of clarity and coherence on large musical peaks. you would get a hardness and lack of cohesion with those belt drive tt’s.....absent with the DD Sirius III, then later the Dobbins SP-10 Mk2, then the Mk3, and then the Koda ’The Beat’ and finally the NVS. yes; piano sustains also could be an issue too. but for me, a lover of big music, it was how those belts handled the peaks that bugged me. you assume that distortion is in the recording....and then hear it sound absolutely right and do the head slapping thing.
which is not to say all belt driven tt's are equally vulnerable to that malady. i know some are not. but it has to be overcome somehow as it's inherent in the approach. |
The most popular motor for the cutting lathes is a Technics SP02 direct
drive motor which is quartz locked for speed accuracy and weighs ~110lbs
with plenty of torque. I doubt this statement. It implies that there are more lathes using the Technics motor (which is great) than those that don't. The simple fact is all lathes unless custom built are vintage machines. Mine is typical- its a Scully built about 1948 or so, equipped with a Westerex cutterhead and electronics from about 1970 (refurbished). The lathe portion didn't see much change over the decades until Scully ceased production altogether- the big change was how the cutter head was advanced across the LP (IOW, when variable groove spacing was introduced) not how the platter drive operates. To that end, the platter is driven by a drive shaft operated by a transmission that has the gear ratios for its two speeds (33 and 45), which is in turn driven by a 1/8th horsepower synchronous motor running at 1800 rpm. The motor, if operated with no load (or external flywheel), takes over 30 seconds to spin down (nice bearings). That, coupled with an external flywheel and the various bits of rotating mass in the transmission as well as the actual ~17" platter, insure that the platter's motion is very constant. In a machine such as this, the proper function of the drive shaft and whether the platter bearings have been properly lubricated and warmed up (the manual calls for a 20 minute warmup time) has a much greater effect on the platter speed stability than any 'cogging' that might be present in the motor! Scullys were one of the most popular lathes in the US for a long time, but there are other types such as the Neumann as well. Except for those that use the Technics drive motor, they all run along similar principles. I've used the Timeline on the Scully; when we were finishing the refurbishment a few years ago I felt it a good idea to see how we were doing. Its pretty stable- but IMO isn't the last word in speed stability or accuracy. It can keep a strobe absolutely still and doesn't vary except when the cutter head touches down to do a cut (which runs about 60 grams of pressure on the stylus). Once touched down the strobe stays put. But the Timeline tells a different story- essentially that the lathe runs ever so slightly slow. How much I've yet to determine since I've not set up the Timeline to present a calibrated assessment. But its clearly close enough that hearing a pitch variation is impossible. IMO, the big issue of stylus drag affecting speed isn't pitch stability so much as it can induce oscillation of the arm over the stylus- in turn causing the tracking pressure on the groove wall to vary left to right and back. As that happens, it induces to my ear a slight 'shimmer' in the soundstage; when you have a 'table that has really locked-in speed, that shimmer is gone and the soundstage is like that which you hear in reel to reel tape. |
I THINK that some of us are saying this: Absolute accurate speed is not the issue. I (and whoever) would agree that I am not able to discern the difference between 33.334 and 33.333. In fact, I know for sure that I cannot tell 33.333 from a constant 33.5 or from 33.2, because I can do that experiment with the Phoenix Engineering Eagle and Roadrunner driving my Lenco motor. What IS potentially audible are VARIATIONs in constant speed, drifting of speed during musical passages especially that feature piano and/or stringed instruments. Whatever technology used in turntable design and build that eliminates or minimizes speed instability (DD, Belt-, or idler-drive) is fine with me. It just so happens that for me the best vintage Japanese DDs and my Lenco do it at lowest cost or best bang for the buck. Belt-drives at anywhere near the same cost have failed, speaking for myself.
Mijostyn, Those rumble filters may be useful if you hear rumble, but in all other cases, they are no free lunch. The filter elements color the sound all the way up the scale, inevitably. I also don't know where you are getting your LPs from, but I rarely encounter rumble that is problematic enough for me to want to engage a high pass (rumble) filter. This is using two completely different audio systems in my home environment, driven alternately by 5 different turntables. I'm not saying "never", but it's rare.
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The 30/12 is an amazing turntable. It’s degree of isolation is better than any turntable I am aware of. while the passive isolation for the 30/12 from all those rubber bands is relatively effective, it is limited. OTOH the overall build quality of the 30/12 results in top level sound, but the isolation component is relatively pedestrian. i think maybe Peter has his 30/12 on a passive air decoupling Vibra-plane platform to improve isolation. that is degrees better than the stock 30/12 isolation, but still passive. for ultimate turntable isolation you need to observe how science does isolation. they use active shelves with piezo-electric sensors and actuators in 6 axis’s. http://www.herzan.com/products/active-vibration-control/ts-series.html as it comes stock for science this product is not fully ready for high fidelity purposes. it has a SMPS which broadcast’s noise into your signal path, plus it’s limited to effectiveness under 200hz so needs further modification to cover the whole FR. and as it cannot discern the source of resonance it attenuates, only tt’s with very low self resonance work well with it. but properly modified and applied to the right turntable it takes things where no passive isolation approach can follow. |
Peterayer, no big surprise. The 30/12 is an amazing turntable. It's degree of isolation is better than any turntable I am aware of. The V12 is IMHO SME's best tonearm. Have you checked your resonance frequency on a test record? The SME is the lightest 12" tonearm I am aware of. It's effective mass is only 12 gms. The Air Tight is almost as stiff as a Koetsu.
My guess is that adding some weight to the head shell might improve your bass a bit. I set mine up for between 8 to 10 Hz.
Guys, chakster has a very valid point. Speed variation is just not a problem for modern turntables because we can't hear it. This is just a spec war. Same goes for lathes but they have to be a lot more powerful and stable because the cutting head causes way more drag and variation in drag than a stylus running in a groove. The big problem with both lathes and turntables is noise particularly rumble which is not only very audible but you can see it! Just look at your woofers dancing around wasting amplifier power and Doppler distorting everything else the woofer is doing. All our preamps use to have rumble filters, just high pass filters 3 dB down at 30 Hz. As I have mentioned in previous posts it is not uncommon for a poorly maintained lathe to rumble. I have had several discs that were so annoying I sent them back. The ones I sent back were all 180 gm "Audiophile" pressings and all were Rykodisc. I have many records that rumble a bit but not so bad that I can't listen to them. I have never been bothered by speed variation and none of the audiophiles I know have complained about it. I think that probably only rapid speed changes would be audible but our heavy platters just can't change speed that fast |
^^^^ up 2 posts @peterayer Peter your findings were very interesting (One table short of a Goldilocks adventure.) Your findings are supported by what Richard said. richardkrebs
The level of granularity we use to measure TTs is simply too crude to show us what is going on in real time under dynamic conditions.
But we sure can hear it. Still IMO, based on my personal journey, "Stylus Drag" is not an Iceberg Scenario, where most of what is happening is below the surface; where this thread is focused. The table and keeping speed. What is happening above the surface is just as, if not more important in regards to Stylus Drag, since I believe the type of cartridge and tonearm pickup used are worth ........hmmmmm..........let's call it 33.333 % each. 8^0 As we know playing vinyl properly requires good setup between the trio of parts. Cheers Chris |
’Very interesting thread. As I read through these responses, I have to wonder if the original recording mechanism, the record lathe that cuts the master from which the molds are made, is equally subject to modulation induced speed variations. ’ @pickindoug- Phoenixengr addressed that exact issue, just four posts before yours. |
I started a thread years ago inviting people to upload videos of their turntables with the Timeline. Lots of promises but no one took me up on the challenge. Here is a link to that thread: https://forum.audiogon.com/discussions/turntable-speed-accuracy/post?highlight=SME%2Band%2BSutherlan...Here is a link to a video of my SME 30/12A with the Timeline: https://www.youtube.com/watch?v=Clwc_c8sVn0Look for the red laser dash on the edge of the LP cover. It is not perfect, as you can clearly see the quality of the laser dash changes slightly indicating micro speed fluctuations, but it is pretty good. I also made a video using my friend's Technics SP10 Mk3 with the Timeline: https://www.youtube.com/watch?v=haqhT6khqZYGreat performance, but when we moved that table into my system and compared its sound to my SME 30/12A using the same arm and cartridge, the SME sounded much more natural and like real music. The belt v. DD debate will go on for a long time. |
Very interesting thread. As I read through these responses, I have to wonder if the original recording mechanism, the record lathe that cuts the master from which the molds are made, is equally subject to modulation induced speed variations. Plowing a new field, so to speak, would seem to take a bit more energy than playing an existing groove. How does the record lathe overcome this? And if it doesn’t, perhaps stylus drag speed variation in the playback system mirrors the speed variation in the recording process........ |
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Mike.
Exactly. This is what I was trying to say with respect to dynamic speed stability, (steadiness)
The level of granularity we use to measure TTs is simply too crude to show us what is going on in real time under dynamic conditions.
But we sure can hear it.
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of course, this is a natural selection problem. far beyond numbers or instruments. my son-in-law is a physicist working for the Allen Institute. they do brain research. he assembles big data for the neuroscientists. he said in maybe 10 years they will be able to replicate a cubic cm of mouse brain tissue. but right now it’s too much data to replicate. he does not think he will live long enough for them to be able to do that for a cm of human brain tissue. just too much data. so when we think that we can measure what our senses have evolved to sense, we are kidding ourselves. and not just the hearing part. the whole body is involved in whether we think something is fake or real. which is why getting as close to absolutely steady as possible means more to our musical sensibilities than what we view as corrected speed. there are no naturally occurring servos. In general, accurate rotation is obtained by servo-control by negative feedback, but at the micro level, if it rotates or becomes faster, it detects it and slows it, and repeats the operation to make it faster if it gets slower. If you try to measure a period with a small level, you cannot measure the instantaneous state, so you should measure the average value. Therefore, fine vibration generated by servo-control cannot be measured by the measuring instrument, it depends on the human ear. |
"Dear friends: I would like to know if each single LP was recorded/cutted
at exactly/accurated 33.333..rpm and if for any reasons exist tiny
deviations from 33.333..rpm accuracy why or how can we or not detected
through an accurate TT that spins at exactly 33.333...rpm during play
time of LPs?" The most popular motor for the cutting lathes is a Technics SP02 direct drive motor which is quartz locked for speed accuracy and weighs ~110lbs with plenty of torque. W&F are rated at 0.0084% RMS. In terms of absolute speed accuracy, it should be more accurate (and more stable) than most of the DD tables playing the LP it cuts. http://pspatialaudio.com/lathes.htm |
chakster.
I said... "I don't claim to be able to hear this difference"
You seem to be agreeing with me?.
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Audiophiles are strange. It is obvious that adults can’t develop perfect pitch ( see why), so most likely none of you can detect such a tiny difference in pitch/tone by ear in a blind test playing records on your turntable. Even professional and very well educated musicians does not have a perfect pitch. How to develop perfect pitch? Watch this. I found it very interesting. If you could detect a difference in tone between 33.333 and 33.334 then you’re not a human, or you must be 1 of 10 000 people trained for a perfect pitch since you’re baby. In other words: If your turntable spinning slightly faster or slower you can’t detect it anyway when it comes to such a tiny difference people describing here above. C’mon: 33.333 or 33.334? Are you serious? Only 1 out of 10 000 people might have a perfect pitch and the only reason for this is because they’re born in a family of musicians and they were trained in the first 4 years of their life. Just watch this video. P.S. I am using top japanese DD turntables with two tonearms on each and all those DDs are stable as hell. Stylus-Drag ? Even if the tracking force is 1-3g, how about 900g record weight we’re putting on top or the record each time we play it? "Stylus-Drag problem" does not exist for me. Happy listening. |
"But I was a bit puzzled by your statement: "A 24 pole motor turns at
half the speed of 12 pole motor so the frequency of the cogs is
identical in both (120Hz)." In a direct-drive turntable, doesn't the
motor have to turn at 33.3333 rpm, regardless of the number of poles?
And therefore might there not be a theoretical advantage to having
double the number of poles?" My statement was in response to the assertion that adding more poles reduces cogging (it doesn't). Doubling the number of poles does not change the vibration signature because it will also cause the motor to turn at half the speed (assuming the same 60Hz drive signal). Both a 12 pole and a 24 pole motor will produce vibration from cogging at 120Hz (10 revs/sec x 12 poles at 600 RPM and 5 revs/sec x 24 poles at 300 RPM). The amplitude of the vibrations is directly proportional to the power consumption of the motor, not the number of poles. If you go to the link I provided, you will see that the measurements bore this out. The motor on a direct drive table does turn at 33.333 RPM so the number of poles will determine the drive frequency needed in that case (RPM=Freq x 60/pole pairs or Freq=RPM x pole pairs/60). If the motor uses steel pole pieces, it is subject to cogging and the frequency of vibration will be 0.555Hz x number of poles; in most cases, this would be below 20 Hz so it will show up as rumble.
To run a DD motor from 60Hz would require 216 poles.
From what I've seen, most of the DD tables use a DC motor with servo control (feedback) to maintain proper speed. This of course, comes with its own set of problems. |
Dear @richardkrebs : "
This is a whole different topic. ", yes diferent but with direct relationship with " audible "/or not speed deviations that we " charge " to the TT culprit when maybe not always came from the speed unstability in the TT.
Perhaps we need a recording engineering to answer the question, that I remember in this moment Atmasphere has enough experience about and maybe he could chime here on it.
In the other side: "
TTs dynamic speed accuracy. """ M.Lavigne posted about " steady " as the critical issue and yes this is the main subject with any TT.
In your example if both TTs are " steady " we can't be able to detect it and maybe we can't even if not steady because speed difference is so tiny.
R. |
