Interested in motor noise and plinths

Discussion in 'Audio Hardware' started by H8SLKC, May 26, 2017.

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  1. H8SLKC

    H8SLKC Forum Resident Thread Starter

    Location:
    Boston, MA
    The majority of turntables on the market include a motor attached directly to the plinth. I've been poking around with my U-Turn Orbit lately, removing covers, examining the works, the rubber motor mount, etc. and noting that there is an ever-present motor vibration/hum that can scarcely be heard with your ear right next to the motor. If I use a screwdriver as a stethoscope (an old mechanic trick) there is clearly resonance that moves from the rubber motor mount and into the plinth. I am unable to hear noise transmitted through the tonearm when I play records although I am confident that if I turned the volume up high enough there has to be noise signal coming through.

    I don't say any of this to pick on U-Turn, but more because it makes me interested in whether it is possible to manufacture a motor, directly mounted to the plinth, that would not transmit noise into the plinth, spindle and tonearm. Certainly listening with a stethoscope, I find it impossible that one wouldn't pick up noise in any plinth to which an electric motor is attached. I read very often about typical models from Pro-ject, Rega, Music Hall and others in which writers/posters complain about motor noise. Is this a compromise that can only be avoided with tables that physically decouple the motor from the rest of the works? What about DD tables? How can they avoid large amounts of noise working into the spindle and tonearm?

    Lastly, I have posted multiple times about trying to keep it simple in this hobby and avoiding the rat hole of audio obsession and fetishism. However, I can clearly see how these sorts of questions lead directly to guys spending obscene amounts chasing things like motor noise they can't hear but KNOW is there. Even though records sound great to me coming from this turntable, and I can hear no motor noise making its way through to the speakers, and in fact can only barely hear motor noise at all even with my ear right next to the belt spindle, it really bothers me that it's there at all.

    I'm not looking for answers necessarily, maybe discussion, but I get it, I get why guys go crazy with this stuff. I read posts about sand boxes, endless sorbothane feet and plugs, spending thousands on "ink black" noise floors, phono preamps, I see how that happens. It starts with questions like mine above. This leads nowhere good.
     
  2. missan

    missan Forum Resident

    Location:
    Stockholm
    All TTs will have a level of rumble and vibrations/noise. It´s not so that some have and some have not. It´s a degree. What one can do, if one is interested enough, is to test the level. One can start with a good test record with silent grooves, record the output from the phono amp, and look at the levels with a software.
     
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  3. jupiterboy

    jupiterboy Forum Residue

    Location:
    Buffalo, NY
    ^ exactly. It is easy enough to measure as mentioned. Even if you put the motor in its own plinth or box, the belt brings the noise along with it. Best to design with materials chosen to keep those noises out of the audible range.

    I'll add that if you can use a test record and look at the signal in real time, you can often find an issue early, like pet hair etc. on the shaft/bearing. It's amazing how quickly a turntable can pick up noise if you don’t maintain it.
     
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  4. patient_ot

    patient_ot Senior Member

    Location:
    USA
    Most companies nowadays (esp. audiophile turntable makers) don't even get involved in the manufacture or design of their motors. They simply choose an off the shelf motor designed for industrial applications, then create a pulley system and try to isolate the motor the best they can. The reason for this is that they lack economies of scale and designing and building motors from scratch would be cost prohibitive. Of course, if you ever need a replacement motor they will gladly charge you a healthy markup many times over their cost for these off the shelf motors.

    DD tables are a different animal, especially older DD tables, but even those had some kind of isolation around the motor even if it was just layers of plastic, metal, and rubber and a thick rubber mat on the platter.
     
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  5. patient_ot

    patient_ot Senior Member

    Location:
    USA
    One of the most interesting designs I've seen is an older Micro Seiki TT with an outboard motor that uses a very long belt, much longer than most turntable belts, even those with outboard motors. I'd imagine that design cuts down on motor noise considerably.
     
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  6. action pact

    action pact Music Omnivore

    This was the solution I chose... eight layers of stacked plywood.

    [​IMG]

    [​IMG]
     
  7. patient_ot

    patient_ot Senior Member

    Location:
    USA
    ^Looks great. Would love to see numbers on that. Wouldn't be surprised if they are equal or better than a lot of newer TTs.
     
  8. action pact

    action pact Music Omnivore

    Rumble is a non-issue, and it has quite excellent dynamics and grip. It also weighs a ton!
     
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  9. Randoms

    Randoms Aerie Faerie Nonsense

    Location:
    UK
    You only have to look at the upgrade history of the Linn LP12, to see the importance of the plinth, the main bearing, the top plate and the motor. Oh, and the turntable sounds different depending which of the 4 potential ways you have orientated the drive belt.

    They also massively improved the power supply, 8 years into production and a major upgrade optional power supply was offered 16 years after the turntable was introduced.

    These are just some of the improvements in the first 16 years of a product that has now been in production, for 45 years! Motor and main bearing noise is not a good thing!!

    Any motor vibration will be transmitted through the belt, into the platter - you get the idea!!
     
    Last edited: May 26, 2017
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  10. jupiterboy

    jupiterboy Forum Residue

    Location:
    Buffalo, NY
    Mine uses a servomotor from the computer industry. You can get a new one on the open market. Uses a custom aluminum pulley. Plinth is MDF lead sandwich. Platter is a polymer sandwich—damping material between essentially two platters. Lot’s of hightech resin and plastic really. Tonearm is a bit more of a manufacturing feat, but you can see how often makers go for a straight shaft rather than tapered, again, expensive to produce.
     
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  11. H8SLKC

    H8SLKC Forum Resident Thread Starter

    Location:
    Boston, MA
    Thanks all for your thoughtful replies! Very interesting and thought-provoking and I'm afraid I may find myself going down the rabbit hole as time goes forward. My wallet hopes not!
     
  12. krisbee

    krisbee Forum Resident

    Here is a video I did where I tamed the Uturn's motor noise by 10db (and actually 25 db prior in another video), showing graphs of the noise and how good I got it...

     
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  13. H8SLKC

    H8SLKC Forum Resident Thread Starter

    Location:
    Boston, MA
    On the strength of your videos I just ordered a sheet of 1/8" sorbothane to do some similar work on my Orbit. I saw that you use it under the turntable feet and two small pieces under the motor PCB. Do you keep the motor housing off of the unit at all times? I was considering placing a piece of sorbothane inside of the motor housing directly underneath the motor, not sure if that might be helpful. Lastly, I saw on the UK iteration of amazon that there are sorbothane kits cut and sized for use in Regas. One of the kits that looked intriguing was a set of triangular wedge shaped slices that are cut to fit in the subplatter spaces between the spines in the subplatter. The U-Turn uses a very similar shape for their subplatter and if I have material left over I my cut small wedges to fit into the subplatter on my Orbit. I don't do needle drops but am very interested in tweaks like the work you've done to make the table as quiet as possible. Thanks for the heads up on your videos!
     
  14. krisbee

    krisbee Forum Resident

    I used them under the feet and then wedged under the motor pcb, but I left everything else the same. I didnt see the benefit to undo the pcb and just leave loose, which may do EVEN better. Wedged in the motor assembly didnt do anything and I like how the motor doesnt really touch anything to begin with. I left the cover on the motor assembly, but only because I felt more comfortable - give it a shot and let me know!

    Oh, and I did also put sorbothane directly on the motor bottom - made no difference as far as I could tell.
     
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  15. rebellovw

    rebellovw Forum Resident

    Location:
    hell
    I've used seismic apps to demonstrate table isolation - that can be pretty revealing.
     
  16. H8SLKC

    H8SLKC Forum Resident Thread Starter

    Location:
    Boston, MA
    Costerdock please do tell more. Are you referring to iphone apps that use the accelerometers in the phone to measure vibration? I'm intrigued! I'm awaiting the delivery of a 12" x 12" sheet of sorbothane and plan to experiment along the lines of krisbee, although I don't have means to measure noise floor the way he does.
     
  17. rebellovw

    rebellovw Forum Resident

    Location:
    hell
    Check out the following post - yep - I used a couple iphone apps

    Pioneer's new PLX-1000 Turntable
     
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  18. H8SLKC

    H8SLKC Forum Resident Thread Starter

    Location:
    Boston, MA
    Super cool. I'll check that out. Thanks.
     
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  19. chervokas

    chervokas Senior Member


    This is kind of the heart and soul of the biggest challenge in turntable design, knocking down the transmission of motor vibration and torque ripple into the platter and tonearm -- btw, I'm sure you are hearing it mixing in with the music even at relatively low levels, any kind of vinyl whoosh or sort of noise of the needle in the groove between tracks kind of think is probably from the motor vibration. It's almost certainly obscuring low level detail. It's also probably causing work tracking.

    Lots of different design approaches folks have used over the years -- different motors with less cogging and ripple (sometimes DC motors, sometimes AC motors with more poles for lower amplitude ripple). Motors mounted to different surfaces than tonearms -- whether in something like suspended subchassis tables or some of the tables that have sometimes been made with completely decoupled stand alone motors (the motor of course is still coupled to the table through the belt, however), etc. My Merrill Heirloom has the motor in a lead pod to contain EMF, and the motor is submerged in an oil bath and there's still plenty of torque ripple without changes to the electronic control of the motor Each different solution comes with it's one challenge. I don't know what kind of motor the U Turn uses. With AC synchronous motors commonly used in lots of turntables, you can dramatically reduce torque ripple by lowering the AC voltage to the motor after initial start up (down to like 72 VAC from 120 or 115). It'll lower torque but that'll lower torque ripple. If the platter has sufficient mass for there to be a good kind of inertia and create no problem with stylus drag, that can help a lot (you can just to it with a Variac). Ideally you'd drive an AC synchronous motor with a motor controller that could allow you to precisely trim the phase between the two legs of the power supply to the motor, and the post-start up voltage of each, but there's no easy solution for that.

    But lowering the impact of motor noise on turntable playback is one of the big differences between good, better and best tables. A lot of it has to do with the motor itself, how it and the tonearm are mounted, the material those things are mounted to, and especially the motor drive mechanism.

    I dunno how the UTurn is build but maybe decoupling the motor with some kind of elastomer-- of course you don't want to change the motor/pully height relative to the platter too much, so it can be tough, depending on the way the motor is mounted, to fit any kind of useful decoupling material between the motor and the plinth on an aftermarket basis and still maintain position. You can maybe try damping the plinth with some CLD type of material -- I've used Second Skin's Damplifier Pro for certain kinds of uses and it works well, something that can convert motion that reaches the plinth from the motor into heat . I don't know what kind of motor it has -- if its an AC or DC motor, but if it's an AC motor you can use a Variac to run it at lower voltage after start up (but of course then you have to buy a Variac which might cost half as much as the table did in the first place so, given the cost of all that, might be better to just move up to the next level of table. Not to slam U Turn or anything, but it is a super budget table).
     
    Last edited: May 28, 2017
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  20. chervokas

    chervokas Senior Member

    Sorbothane is a elastomer that works by, when it's properly loaded, converting motion to heat. It's really better for footers for environmental isolation and that type of thing than damping a platter or subplatter. Not the right material for that application -- if you put the sorbothane between the motor and the plinth without squishing it down too much (if you squish the sorbothane it won't be able to do it's thing and it'll just be coupling not decoupling) -- that might help. To damp a sub platter, or platter, or plinth, you'd be better off with a CLD material for that I think vs. sorbothane. Also, doesn't the UTurn drive the platter directly with a belt? The Rega drives the subplatter. I dunno if damping the subplatter on the UTurn will have the same impact it does on the Rega since the UTurn platter is directly coupled to the motor via the belt. Also coupling the motor to the platter may not be the big problem, it may be the coupling of the motor to the plinth to which the arm is also coupled. Might be better to damp the plith with a CLD material.
     
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  21. Randoms

    Randoms Aerie Faerie Nonsense

    Location:
    UK
    @H8SLKC @Dream On This is one of the real dilemmas of turntable designs, trying to keep a platter rotating at a steady speed, under a dynamic load (the drag of a stylus), without extraneous noise and vibration, which as chervokas points out, obscures low level detail.

    Manufacturers have tried all kinds of drive, isolation and motor design, some for cost, some for performance, on a high end turntable for both cost and performance. AC motors, DC motors, battery packs, jockey wheel drive, belt drive on inner platter, belt drive on outer platter, direct drive, and quartz locked, servo controlled.

    One of my favourite upgrades that I ever introduced into my Hi-fi system, and also sold multiple dozens of, was the Linn Lingo power supply. I'm taking Linn, the LP12 and the Lingo as an example here, because I've done this demonstration so many times, always with the same result. At a certain level, improving the motor / power supply, should give improvements to all turntables, given a good fundamental design.

    Using 90s pricing, why would you use a £300 power supply, to drive a sub £50 motor? Why would a LP12 with Lingo and budget tonearm, outperform a LP12, sans Lingo with a far better arm? Apart from the obvious answer that the power supply comes earlier in the chain, an explanation, from Linn on how the Lingo operates, and what it does, makes some sense of this cost / performance balance.

    The Lingo, was an optional upgrade to the Valhalla power supply, which had already given a large improvement to motor drive.

    From Linn, the Lingo has these features:
    Low noise oscillators
    Precision filtering
    Separate drive for both motor phases
    High isolation from mains supply
    Both 33 and 45 speeds!! (My exclamation marks)

    "The LP12 motor runs quietest when driven with a clean sinusoidal waveform.....
    The most uniform torque is delivered from the motor when both phases are driven at 90 degrees with respect to one another. This is achieved.....

    The Lingo uses "stall detection" circuitry to feed the motor higher voltage for increased start-up torque. When the platter reaches the selected speed, this load-sensing circuitry reduces the power output. From then on motor just maintains the platter's own inertia, to keep it going silently."

    This is the lengths manufacturers will go to reduce vibration and the subsequent loss of detail, which @chervokas mentioned.

    I'm certainly not suggesting that everyone should rush out and buy an upgraded power supply, though once you have got a certain level of turntable, that could give a big improvement, just to give more information for your interest in motor noise and vibration. This is just one part of isolating a turntable from both internal and external noise and vibration.

    On a turntable with a suspended sub-chassis, the motor is further isolated from the motor.

    I personally believe that the amount of information on a record is staggering, and we are still finding ways to retrieve more of it.

    GIGO!!
     
    Last edited: May 29, 2017
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  22. missan

    missan Forum Resident

    Location:
    Stockholm
    A good way to start is to analyze rumble, hum and noise using a test record with silent grooves.
     
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  23. H8SLKC

    H8SLKC Forum Resident Thread Starter

    Location:
    Boston, MA
    I thought I'd post an update to all of the above. I bought a 12" X 6" sheet of 1/8" sorbothane. I've used only a tiny portion of it so far and basically applied it wherever it seemed it might do any good. I wedged little pieces under all four sides of the motor PCB like krisbee showed in his video above. I applied two small wedges under edges of the pluto preamp as well. I created a circular piece to lay in the bottom of the motor/PCB cover so that the motor sits directly above the sorbothane circle, but doesn't touch it. I even placed several shaped pieces on/around the tonearm base, of course not touching any moving components. Then, just because I was having fun cutting out shapes, I created wedge shapes and placed them in the "trays" in the subplatter and created small slices to place in the opening between the spindle and the acrylic platter itself.

    All of this made no difference to the tiny bit of motor noise I was hearing when I put my ear next to the motor spindle, but it was fun nonetheless. Now, the next day I decided to remount the 2m blue cartridge on the tonearm, having been listening to a different cart of late. I had taken off the turntable cover and when I started the motor without the belt attached, it was silent. Hmm. Then I attached the belt and started it again. Silence. What? Then I reattached the lid and found that the tiny bit of motor noise that I hear when running the table is actually reflected energy seemingly focused by the lid, or a vibration running up and through it. It's clear as day, in that the lid being on brings an unmistakable but tiny motor noise, taking it off makes the table run silently.

    All of this brings nothing new to the table of course, knowledge-wise, but it's been fun to play around with the sorbothane and even more fun to find that when I want, I can take the lid off and have a very, very quite turntable. Krisbee, do you use the lid on your machine? I'd be interested in other Orbit owners and whether any of this tracks with their experiences.
     
  24. krisbee

    krisbee Forum Resident

    I believe the motor is 24 vac, answering a post above. The motor sits in a rubber cup, so it is slightly isolated from the plinth, basically floating in air. I have done my measurements with and without the belt on, getting similar results. Basically -65db was the best I got on the table. Interestingly, I posted a screen cap in that video, that I got a WORSE result having the lid off, which was how I was doing needleddrops, by -5db (if I recall). One thing I didnt try was wedging sorobothane on the TOP of the feet, just the bottom...
     
  25. Eno_Fan

    Eno_Fan Staring into the abyss: Brockman BIF, Pilbara WA

    Location:
    Izieu, France
    Interesting stuff -- I tried broaching these very issues in the current thread 'Rega Planar 6 measurements! ' to a lot of ridiculous comment about "...listening with stethoscopes" from all the Rega fanbois who are already financially committed and haven't heard better. As I said there, when I compared a stock Planar 3 against my suspended-subchassis STD 305M at audition the Rega was almost laughably inferior, a result that I put down to lack of isolation of the plinth (thus arm and cartridge) from the motor. That magazine reviewers (e.g., Reichert, Fremer) are all now detecting by stethoscope large amounts of motor noise transmitted to the arm in such hard-coupled designs as the Planar 3, RP8, MoFi, etc., speaks to the ubiquity of this problem in today's un-engineered bolt-a-motor-to-a-piece-of-MDF cheapness of manufacture (if not of eventual sale-price).

    As I asked in that Thread, what do all of the worlds greatest TTs, e.g., Air-Force, Rockport, Verdier, etc., have in common? They decouple the platter from the motor.

    What do Rega do? They couple that motor as tightly as they can to that platter.

    This light-and-rigid MO is Roy Gandy's idée fixe. It will never change, even in the £30k Nalad.

    I've long thought that the only real solution to this problem would be a full passive-magnetic bearing (i.e., thrust-plate AND shaft) supporting a massive platter brought up to speed by induction and then powered down and allowed to rotate under inertia (platter-mass determined by stylus drag over 30 mins). Until recently, the closest that magnetic bearings came to this ideal were the partial-magnetic bearings (CMB) of Clearaudio, but Mag_Lev have taken a big leap forward with their fully-levitating ML1 turntable that also drives the platter by magnetic repulsion. No motor, no contact, no rumble and, by early accounts (e.g., MAG - LEV Audio ML1 Levitating Turntable - Positive Feedback ), nothing really like it sound-wise for anything like the small amount of money required. I contacted them regarding the fairly sloppy as-released performance of their platter in terms of variably-unconstrained tilt around the axis of rotation (the platter 'wobbles' up and down while rotating) to no reply, and I think that the current execution is substandard in terms of needing to be powered down and the platter supports thus racked-up for every side-change, but this concept, properly executed (and with a levitating arm-mount), could easily become the best TT in the world for a couple-of-grand. Such a device should truly have 'no sound of its own'. Quite extraordinary, and something to watch...
     
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