A few mods to my LP12

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deano1712

Member
Joined 2020
analog_sa said:
My A-max started behaving the same way and i assumed the negative resistance circuit was to blame. The driving voltage is very stable when the motor is idling but once it has to drive the platter the driving voltage starts constantly changing. I assumed electric instability but perhaps it is the brushes contact resistance that is changing as the motor spins under load and the drive system just tries to compensate for that.

Many thanks for your observations and disclosing the response from Maxon. The motor used in the Continuum is said to be a 60v, carbon brushes model which is a little at odds with the gold flash.

Perhaps even the OL Maxon based kits use an off the shelf motor. Inexplicable that Maxon would not have a regular motor suited for low rpm work.
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What brush type did you have in the A-max? If precious metal it sounds a similar problem to my own.
Vermouth said:
Interesting approach from Continium. That's the original Maxon Eschon 36/3 controller they are using. But 36mm 60v Motor with ball bearings and graphite brushes.


"The 35mm, 60-volt DC motor was designed and manufactured specifically for optimum performance with Obsidian’s platter mass and physical harmonic characteristics. It combines a set of specifications uncommon for low-noise applications, but that combine to deliver exceptionally smooth operation and the highest power currently available in a motor of its size. Its zero-cogging motor is controlled by a servo amplifier running at 53.6 kHz, far above the range of audibility.

The Quiet One uses stainless steel pre-loaded ball bearings. Why ball bearings, when sleeve bearings are typically preferred for low-noise applications? Because sleeve bearings do not have the load handling or durability of ball bearings—and through careful design, our dream team was able to ensure that any vibrations created by the bearings would be damped by other components in Obsidian’s structure.

The Quiet One uses graphite brushes. Why graphite, when precious metal brushes are typically preferred? Because precious metal brushes often do not have the current conducting capacity required to drive a heavy platter—and because our dream team created a special damping system, calibrated precisely for the motor’s speed range, that attenuates brush noise."
http://www.continuumaudiolabs.com/turntables/obsidian/innovative_motor.php
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This is really interesting. Use of graphite brushes and ball bearings is normally considered to worsen vibration but if they make it work then great. It would be good if graphite brushes are immune to the degradation I have experienced, in which case that’s the way forward for us diy folk when selecting a dc motor. Graphite brush motors spin faster and have a higher speed constant so a higher voltage motor would be needed. A DCX22S 48v graphite motor has similar speed performance to a 24v PM brush motor.
 
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deano1712

Member
Joined 2020
srinis said:
Thank you very much for the information and the drawing. Really appreciate it.
I took the Sheet Metal Sub-Chases dimensions on a CMM and wanted to make a drawing with the photos as you did. But you saved all of that. I will see how to go forward with manufacturing.
Kindly suggest if you have any information on which aluminium alloy is better. Does something like 6061-T6 or 2014-T6 works?
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Just be aware the model was created for analysis only so if you want to use this to make a part the geometry needs thoroughly checking.

I think any aluminium will do its the density and stiffness that’s important and all normal grades have very similar parameters.
 
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