High quality AC turntable motor

Redglobe,

From a cursory glance, I would say that the Sound Carrier unit is very similar to either the Walker or the SDS (with the added ability to trim output voltage). Hence, no - I don't believe the unit to offer full parametric adjustment, far from it in fact. The Heed Orbit would fall into this same category as well.

To give you a better idea, my Kelly controller has approximately seven trim pots that can be adjusted to not so subtle effect. Of course, this excludes the speed selector switch, frequency setting 'switches' and the on/off switch. I do not, however, have a fancy meter on the front of my controller ;-)

Grbluen2,

I'm afraid I can't be more specific about building a parametric two phase controller from the ground up. The easiest way out would be to use two MP3 players with continuous sinusoidal waveform loops (of differing frequency for speed selection) fed through a cheap (maybe class D) amplifier such that one could vary the output amplitude (voltage) for each phase (IMO, this is the most important parameter to adjust). While this doesn't give one full parametric control, it is essentially the idea behind the first controller I mentioned (http://www.soundbound24.blogspot.ca/). It uses a chip which contains the command set for generating sine waves of varying frequency (speed), lagging one phase behind the other, changing amplitude and (were the builder to incorporate it) varying harmonic distortion components. In all, he's on the right path. The devil of course is in the details.

Lewm,

What I was getting at was that ac controllers that change speed between 45 and 33.3 without splitting the phase cannot really do a good job. The capacitor that then does the phase split/rotation, cannot be of the right value to do the job correctly for two different frequencies. That is why I think that plug-in motor controllers that electronically switch speed are of dubious value. The right way is for the controller to do the splitting optimally for whichever speed, in which case, there are, in effect, two separate supply lines leading from the controller to the motor (the capacitor is then removed from the motor).

Palasr, I once wondered about modifying one of the early type PS Audio P300 power plants, such that one can attain a wider and continuous control over frequency. That plus a few other tricks might make it useable as a 2-phase controller. I think it already has an optional 2-phase output. (The waveform of the AC output can be adjusted.) In stock form, the frequency is only adjustable in discrete steps, up and down from 60Hz.

Some years back, I designed/built a little sine/cosine generator based on the B-B 4423 chip. Long discontinued but old stock can sometimes be found.

If interested, you can see the datasheet here: http://www.icmaster.com/PartDetails.aspx?Part=1440941204&InStock=False

Kal

Palasr, I'm sorry for not being clear. I can generate quadrature sinewaves, with the ability to vary the phase and amplitude of the waveforms. My question was, now that I have two waveforms and the ability to vary phase and amplitude, what is the procedure for finding the magic setting. Are you measuring the speed distortions of the platter as a result of some sort of systematic tweaking of the waveforms.
Don

Posted 11:53 AM 28-NOV-2012