Oracle motor/controller problems - DIY turntable

I've built a turntable using the motor, controller, bearing and sub-platter from an
Oracle Alexandria table that had been scrapped because of frame problems.

I put the motor in a separate pod, mounted the control board into a box and
ran a (cassette tape) belt to the sub-platter. The motor is spinning WAY faster
than it is supposed to be and the buttons for 33, 45 and pitch don't seem to
have any effect. The motor also has a whining noise at speed which I don't
think should be there. I don't know if these pieces worked properly before I took
it apart. Any ideas on what I could do next?
 

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DIY turntable pictures

Thought i would post a couple of photos of the turntable without the motor and control box.
It has an air-bearing arm - Ladegaard style - using aluminum, wenge, carbon fibre, epoxy. Platter is acrylic, lathe turned. Plynth is solid padauk, wenge, aluminum, baltic birch ply sitting on wenge cones. The base has sand-filled 2.5 inch diameter aluminum tubes, a sandbox made of wenge, with a slab of Ubatuba granite.

Don't know how it sounds yet! Need help with the motor!
 

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g-horn....don't even try to make it work...YET!

Let's have a look at the complete electrical system. It almost sounds (sorry for the pun, not intended) like the power supply is putting out AC, or it is being rectified as voltage *sqrt(AC voltage). DC motors get quicker when more voltage is applied. I'll stop right now, but will look directly for my manual and also try to get some voltage numbers off of my power supply and Dynamic Isolator.

OK here's the results of the voltages. Power supply outputs 33 VDC, the "Dynamic stabilizer" puts out 23.8 VDC (at least at my house, but I think the motor is a 24 VDC one actually). My guess is that when set to 33 1/3 rpm, your turntable is spinning at about 46 rpm. Sound about right?

so a couple of alternatives: Get a "Dynamic stabilizer" from whence your turntable parts came from, or build or get a rock stable 24 VDC power supply. Surplus shops may be able to help you out there (or 2 12V sealed gel batteries, and a trickle charger). Then give it a try. Do you have a strobe disc or other means for checking speed accuracy?


stew
 
Thanks for your help on this Nanook, much appreciated.

I measured 33 VDC as well at the power supply. I'm still waiting to hear back from the seller about the missing stabilizer. If it is unavailable, I guess I will try to source a 24 V power supply.

I printed out a strobe disc and a parts list for that DIY hand-held strobe but i haven't got around to making it yet.

Cheers,
Mal
 
I'm told that since the controller contains a LM317T regulator it doesn't require the Dynamic stabilizer box. I'm going to check my wiring again but apart from that, I'm in over my head.

What kind of power supply should I be looking for if I still can't make this work? Is there something off-the-shelf that could be recommended or does someone have a plan for a simple DIY project?

Any thoughts would be appreciated.
Cheers,
Mal
 
a couple of ideas....

well the circuit must be accessible (seeing as you created anew plinth for it).

First step. Try a new voltage regulator, if handy with a soldering iron. 317s are cheap.

quickest simple, cheap "check, is to disconnect all the controls and the voltage to the motor. Use a fairly robust power supply (the Oracle one is something like 300 mA only) at 24 V--Princess Auto often has quite a few at very inexpensive prices. Try it, connected directly to your table (through a fuse if possible). There will be no speed adjustment available. With a potentiometer you should be able to get to speed correctly, as long as you are getting 24VDC or greater, and have a strobe disc, and/or test record. You could use an inexpensive DVM permanently attached to the circuit to allow you to make notes as to where the speed is stable at 33 1/3.

Or go get a high quality "lambda" or similar 20-30 VDC scientific grade power supply online or at a surplus, or something similar that will allow you to finely adjust the output DC

or build yourself a rock solid, absolutely stable 24VDC power supply.
 
Thanks for the suggestion Dan. How hard is it to get into the motor to check that connection? The bottom plate looks like it is pressed into the motor housing and there's no way to grab it. Any thoughts?

I would appreciate the wiring schematic if you don't mind.

Question: There is a fairly audible whirring sound coming from the motor when it is spinning. Is this motor shot?

Mal
 
Interesting, I did the exact same thing that you have done. My speed is fine though. There are photos in this thread. http://www.audiokarma.org/forums/showthread.php?t=116987&highlight=oracle+kenwood

I have a dynamic stabilizer that was actually making speed vary all over the place. Its nothing but a box full of electrolytic caps. I would be happy to take a snapshot to show everyone if you want to build one.

My motor is silent when running.

I have to get off my butt and finish it. I have everything squeezed into a kenwood KD-2055 plinth. Looks decent, but I really need to finish it properly.

Are you sure you have the right power supply? A buddy of mine mentioned that there were actually several different output voltages on the oracles.

Evan

Who did your acrylic platter and how much was it? If you don't mind me asking!
 
At this point I've pretty much given up hope for the Oracle motor/controller. I bought a Lab style variable voltage DC power supply and I have a Maxon 110191 motor on its way. I've also got a Teres controller on order. I think this should get me up and running.

As for the platter, I bought two pieces of 1.5 inch thick acrylic ($60) and laminated them together. I roughed out the circle on the bandsaw, then turned it on a big wood lathe (in my brother's custom cabinetmaking shop). The platter is surprisingly true! I took the platter and the plynth to a local machine shop to have the bearing set in.

I have one of those Kenwood rock tables downstairs too. Looks like you've done a great job with your upgrade!

Mal
 
Thanks for the compliments. I had alot of restrictions in tools to make that table work (I live in an apartment and don't have decent tools here to do fab work).

Ill probabally stick with the oracle platter since its in good shape and has the clamp. Your using the oracle bearing right? I was going to have mine re-machined. The spindle does not fit all that well. It uses a thrust plate in the bottom, but was wondering if there was a way to incorporate a ceramic ball or something of the like. My thrust plate shows wear, and the platter does not spin as freely as I feel it should.

I have a buddy who may want to buy your extra oracle parts. Drop me an email if thats the case.

You have done a great job on your table, you should be proud!!


Evan