1. Time for some upgrades in server hardware and software to enhance security and take AK to the next level. Please contribute what you can to sales@audiokarma.org at PayPal.com - Thanks from the AK Team
    Dismiss Notice

Weird speed issue on Oracle Paris

Discussion in 'Turntables' started by cmcguire, May 16, 2018.

  1. cmcguire

    cmcguire AK Subscriber Subscriber

    Messages:
    131
    Now that I've finally finished the task of scooping all the honey out of my tonearm reservoir and setting out ant traps (if you're not aware of my experiment, please don't ask) I'm on to the task of getting my Oracle Paris up to proper speed. Here's my issue: as measured with the rpm app on my phone every revolution or so the platter speed goes up and down from 33.1 to 33.5 consistently. I've tried it with another phone and the phenomenon is consistent.



    I've just installed a new belt and cleaned all surfaces the belt contacts. I'm thinking it could it be the motor- the speed controls seem to be functioning properly but don't effect the variation in speed, they just slow or speed the whole process. The motor pulley looks to be straight and clean but might do with a polish. Has anybody ever seen this before?
     

     

    Please register to disable this ad.

  2. marcmorin

    marcmorin AK Subscriber Subscriber

    Messages:
    9,153
    buy a strobe disk. not a chance in hekk you have that phone centered on the spindle
     
  3. cmcguire

    cmcguire AK Subscriber Subscriber

    Messages:
    131
    I do own several good strobe discs and yes, a bit of a "jump" can be seen. The phone actually doesn't need to be centred to work, I've just done it for the purposes of the video.
     
  4. marcmorin

    marcmorin AK Subscriber Subscriber

    Messages:
    9,153
    something isn't straight, or something may be out of balance. either/both could give you that orbital slingshot
     
  5. cmcguire

    cmcguire AK Subscriber Subscriber

    Messages:
    131
    I think I'm in slightly over my head. I removed the circuit board cover and found two little trimmer resistors. I have no idea what they do but I have a feeling they control the voltage to the motor. Turning them definitely effects the speed fluctuations but since I don't know what they do I'm just guessing. Can't seem to find a service manual anywhere. Also, while messing with them I made the platter turn backwards, so that's um, something!
     
  6. bang4buck

    bang4buck Well-Known Member

    Messages:
    850
    Location:
    New England
    First off, I would try that phone on another TT to see if it can be trusted in the first place.

    Second, all that matters is what it does when playing a record, so I would repeat the test with the needle in the groove.

    If it does still fluctuate, once per revolution indicates a problem with the platter and/or bearing, not the motor.
     

     

    Please register to disable this ad.

  7. cmcguire

    cmcguire AK Subscriber Subscriber

    Messages:
    131
    Yes, I have tested it on another table and it works reliably. The fluctuation is very audible on my CBS test record so unfortunately it's not acceptable. I've contacted the fine folks at Oracle, I'll post when I hear a reply.
     
  8. ripblade

    ripblade Super Member

    Messages:
    2,613
    Location:
    Toronto
    Was the belt sourced through Oracle? If not, it should be. Otherwise, check to make sure the bearing is properly lubed. Problems in the speed control circuitry tend to produce random fluctuations, not cyclical or periodic ones, such as what I think I see in the video.
     
  9. cmcguire

    cmcguire AK Subscriber Subscriber

    Messages:
    131
    Hi tnsilver, I lubed it with oil sourced from oracle and had the suspension leveled as per the instruction manual.
    I've used three different phones and they've all manifested the same thing so unfortunately it's the table.
    Hi ripblade, it's a new belt from Oracle.

    I'm gonna take it apart and clean everything again- hopefully I'll spot something I missed.
     
  10. tnsilver

    tnsilver AK Subscriber Subscriber

    Messages:
    2,992
    Location:
    Boston
    You almost make it sound like it was a good idea to futz around with the trimmers. It wasn't. You need to check the voltage to the motor on each winding and adjust the trimmers to the same voltage. It's a low voltage synchronous motor so I guess it would be around 5V.
     
    cmcguire likes this.
  11. cmcguire

    cmcguire AK Subscriber Subscriber

    Messages:
    131
    Duly noted, and yes dumb idea. And because I obviously need some hand holding, where/how would I check the voltage?
     

     

    Please register to disable this ad.

  12. cmcguire

    cmcguire AK Subscriber Subscriber

    Messages:
    131
    Update! I received this from Martin at Oracle today:

    "The fact that you noticed that the platter started spinning in the wrong direction tells us this is a Paris with a AC synchronous motor, the DC motor cannot spin in the wrong direction, and that your Paris is most likely a MkVI… The speed direction is set by a polarity trigger that is composed of a capacitor, and it is not impossible or abnormal that this happens from time to time, it only has to do with the polarity of that capacitor upon startup…"

    Great folks at Oracle. If I can't get this sorted I'll sending my Paris to Sherbrooke for a spa day.
     
    bang4buck likes this.
  13. tnsilver

    tnsilver AK Subscriber Subscriber

    Messages:
    2,992
    Location:
    Boston
    Yes, good luck with that. A "polarity trigger" is just a fancy name for a bog plain dollar worth of phase shift capacitor which gives one winding a half cycle head start over the other so the motor starts spinning in the right direction. These don't go bad for decades unless they're inadequate quality to begin with or get zapped by higher voltage than their specs. You can replace it on your own if you can solder but I doubt it's the problem. It's more likely you've thrown the voltages to the motor sides so off, even the phase shift cap can't fix the now biased pull. In any case, it's got nothing to do with your initial alleged speed fluctuations (providing they are real) which can be mechanical, just the same as electronics related, in which case, you've just aggravated the problem.
     
  14. cmcguire

    cmcguire AK Subscriber Subscriber

    Messages:
    131
    The speed issues are absolutely real, I'm cursed with absolute pitch and am therefore very sensitive to speed-pitch variations. This morning I used the multimeter and got the voltages set so that it's back to exhibiting the same phenomenon as can be seen in the video.

    Back to square one. This lead me to think that your suggestion that the problem is merely mechanical is the most likely. I made sure the suspension was set so that the plinth was level and on a whim raised the pulley very slightly on the motor spindle. Eureka! The speed remained stable, that is, until I moved it from the work bench to my listening room.

    Back to square on again. Removed the platter, reinstalled the belt (the pulley had not moved from its reset position) and again the speed was stable for about five minutes of run time and then the drifted out again. Looking between the plinth and the platter I can just see that the belt is drifting up and down the pulley ever so slightly. It's a one piece platter so the inner and outer sections are integral and its therefore really difficult to see what the belt's doing in there.
     
  15. cmcguire

    cmcguire AK Subscriber Subscriber

    Messages:
    131
    That's most likely the problem as the mounting system is as simple as a small square of tacky, spongy, polyurethane material. Think mouse pad with pressure sensitive adhesive on both sides. So, to follow your logic, this material has gotten tired, or unstuck, or both. It's temporarily raised or straightened when I alter the position of the pulley and ultimately settles back into its previous position over time. I'll investigate tonight!
     
    tnsilver likes this.
  16. bang4buck

    bang4buck Well-Known Member

    Messages:
    850
    Location:
    New England
    cmcguire likes this.

     

    Please register to disable this ad.

  17. cmcguire

    cmcguire AK Subscriber Subscriber

    Messages:
    131
    Hi bang4buck, I did check out the thread and it's a fun read so thanks for pointing me in its direction!. I think the parts being discussed were the little rings in the suspension (which I need as well), I was talking specifically about the little square sticky mat that sticks the motor to the plinth. It's actually a really crude but effective system- it's basically a square of thick double sided mounting tape. I'll put up a pic as soon as I get the table apart again. I'll post over there and see if anyone knows of a replacement material.
     
  18. Montycat

    Montycat AK Subscriber Subscriber

    Messages:
    17,388
    Location:
    Vancouver
    I don't know that exact mounting pad but Rega has gone to something similar with their motors rather than the 2 rubber band suspension.
     

Share This Page