Oracle motor/controller problems - DIY turntable

[g-horn]

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?

[Nanook]

The Alex has a two piece (as in two box) power supply, besides the internal electronics to switch speed (if it was an Alex Mkll). not sure if that helps. Someplace I have my manual....

[g-horn]

Hi Nanook
There weren't any other parts in the box related to the motor or supply. Is it a voltage stabilizer that I need? I can ask the guy that I got it from if he knows of its whereabouts.

Are there any work-arounds if it can't be found?

[g-horn]

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!

[g-horn]

Another photo...

[Nanook]

but did you use the Oracle's inner platter?, gimme a pix if you did or didn't please if possible.

Great looking Ladegaard arm!

thanks

stew

[g-horn]

Yes, the acrylic platter sits atop of the Oracle sub-platter. I had a machine shop with a CNC machine set the piece in. I've attached a drawing.

The control buttons won't even switch off the motor any more. Motor spins very fast.

[Nanook]

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

[g-horn]

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

[g-horn]

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