Weird speed issue on Oracle Paris

cmcguire

Active Member
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?
 
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?
buy a strobe disk. not a chance in hekk you have that phone centered on the spindle
 
buy a strobe disk. not a chance in hekk you have that phone centered on the spindle
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.
 
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.
something isn't straight, or something may be out of balance. either/both could give you that orbital slingshot
 
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!
 
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.
 
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.
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.
 
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.
 
It's too bad b/c the owners manual warns about possible quirks due to leveling/lubrication/platter insertion etc... right at the beginning.
Hi tnsilver, I lubed it with oil sourced from oracle and had the suspension leveled as per the instruction manual.
Of course it's also an indication of a bummed TT speed. The problem then is, you actually never know which
I've used three different phones and they've all manifested the same thing so unfortunately it's the table.
Was the belt sourced through Oracle? If not, it should be.
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.
 
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.
 
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.
Duly noted, and yes dumb idea. And because I obviously need some hand holding, where/how would I check the voltage?
 
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.
 
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.
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.
 
I suspect your motor mounts are a little soft
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!
 
You should really drop by in the general Oracle thread: http://audiokarma.org/forums/index.php?threads/the-official-oracle-turntable-thread.807710/page-5

We actually had a report of those motor mounts failing, in posts #59 and 79. It was an earlier version of the Paris, though.
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.
 
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.
 
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