I would consider a PS that has two outputs, one for each field coil of the motor. It should provide the user with the ability to trim the phase angle between the two outputs. The benefits of such an arrangement? The ability to reduce vibrations to almost zero. Removing the vibrations could provide more sonic improvement than a motor change. A high torque motor that vibrates will damage the sound more than a low torque motor's vibes.
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As others said, and I agree, a good motor controller that mates well with your stock motor will probably do you more good than a new motor with higher torque. Townshend turntables in general are well regarded and well designed. I would therefore guess that the motor is quite adequate to do its job as is, but there is much to be gained by feeding it properly. You might ask the designer for suggestions from among the commercially available motor controllers. Anecdotally, I can tell you that a Walker Audio Motor Controller completely transformed the sound of a Nottingham Analog Hyperspace that I once owned. I was shocked at the improvement myself.
Kevin Carter of K&K Audio has a prototype PS that has two outputs with phase angle adjustment. The only thing holding him back from releasing this as a kit is the need to assemble one so he can write up the instructions. If enough people were to email him that might provide the motivation to finish this project. The price of the kit should be reasonable compared to commercial units and it should be sonically superior to all the single output PSs out there.
The Townshend Merlin costs over £1200 UKP - and is essentially a mains sine wave re-generator. I contacted K&K - Kevins a nice guy BTW - his design, which is scheduled for next year, seems to follow the principle of the Rega P9 power supply that smooths out the power by angling the power into the motor to prevent the cogging. I am grateful for the feedback from the motor experimenters!
Whilst I understand that there is a school of thought about getting up to speed, and then simply maintaining it approach, I am beginning to be drawn down the high torque route. I am beginning to notice slight drag in very heavy and complicated passages on my current deck, which is why I wanted to use a higher torque option.
Just a thought, but have you tried a new belt and a good cleaning of the motor pulley and subplatter belt contact area? The stylus drag you are hearing sounds like compliance being introduced through belt slip or stretch.
If you can find one, I've found the Berger-Lahr motors to be considerably better than the Crouzet, Hurst or Saia, at least in terms of cogging. Unfortunately, the Airpax/Premotec motors are rather difficult to source however they offer the smoothest cogging characteristics out of any of them. Then again, I use a Mark Kelly Synchrotron controller, so I can null out most motors so that cogging vibration isn't too much of an issue.
Good luck and keep us posted.
Hi Lewm - sorry for my lousy phrasse 'angling the power' I understand that with a 24 pole synchronous motor they can be made with 4 coils. If 2 opposing coils are driven, and then the other ones which sit at 90degrees to the driven ones are also driven then this ought to significantly reduce the ripple. PErhaps a fair analogy would be a two stroke to a four stroke engine. If it is the case that we have a higher torque motor, it's the magnets that help increase the torque, along with the commutator windings and thickness. As this increases, so does the clunking/cogging. That is why I want something that helps reduce this. A pure sine wave regenerator simply re-creates the 50 hz - it does not provide me with those 90 degree opposed waves to drive the other 2 coils. I hope that I make sense andd am barking up the right tree.
It seems to me that some of the posters here have forgotten some of their Trig. A complete sine wave cycle is 360 degrees. As the previous poster stated one set of field coils is driven by the primary AC current and the other with a AC current 90 degrees out of phase. This phase shift is usually accomplished with a capacitor (the current though a capacitor is 90 degrees out of phase with the voltage across it). Now, a sine wave generator with TWO amplifiers (thus two outputs), one 90 degrees out of phase, with the ability to "trim" the phase angle between the two has the ability to null out almost all motor vibrations. This is a distinct advantage over those sine wave generators with just one output. I own a Nottingham Wave Mechanic. I recently had it open to replace an output transistor that failed (it doesn't do too well with a single ended output stage). There is NOTHING special here. If the parts cost more than $125 I'd be surprised. Yet it retails for something north of $1200. They don't call us Audiofools for nothing. That's one reason I'm committed to DIY. Kevin's kit should provide a lot more "bang for the buck". The OEM power supplies are usually nothing more than an oscillator, a cheap amplifier and a transformer to boost the voltage output of the amp to 120V.
I am reading this thread with interest. The technical knowledge of some here, amazes me.
Having upgraded my turntable system to a three motor controller:
In this German webpage, they discuss another turntable controller with amazing results. Seems like a real bargain compared to other controllers. http://www.frank-landmesser.de/hoer_analog_netzteil.html
I am very happy with the speed accuracy of this type of motor controller.
Still settling into our new house after our move back to the US from a lengthy tour of Europe.
Bpoletti, turntables that use AC are of the synchronous variety. Their speed is determined by the frequency of the AC, not it's voltage. The way AC line voltage bounces around a motor that depended on it for speed regulation would do a lousy job. See: http://en.wikipedia.org/wiki/Synchronous_motor
All this talk about phase has to do with reducing motor vibration, not speed regulation per say. Vibration can add a form of frequency modulated distortion, a form of analog "jitter" if you will.
Interesting to refer to motor mechanics in terms of digital distortion. The "pulsing" you refer to is known as cogging, which refers to the rotation of the rotor through the fixed poles (stator) on a synchronous motor. Depending on the rotational speed of the motor, the number of poles varies; a 300 RPM motor will generally have 24 poles, while at 600 RPM, there will be twelve poles. The overall torque of the motor is determined by the field strength of the magnets; stronger magnets have more cogging and hence more torque.
I find that with most 115VAC synchronous motors, run at their approximately nominal frequency (50/60Hz), it's usually better to smooth out the cogging by running the motor at approximately 65-75% of its rated voltage. For example, I run my 600 RPM/115VAC motor at 55Hz for 33RPM with a voltage around 75VAC on one phase, and around 69VAC on the other. This optimizes the torque to cogging ratio such that the motor doesn't introduce vibration through the drive chain, yet maintains enough torque to overcome all stylus drag during heavily modulated passages.
The SDS is a decent controller, but its lack of parametric adjustment (phase angle, harmonic distortion, and individual phase amplitude) makes it nothing more than a glorified speed controller (though nice for a VPI owner to not have to swap pulleys). It does little, however, to address the differences found even in sample to sample runs of the same exact motor. Without being able to optimize every parameter of the motor, you can never really null out cogging, nor get the best performance out of any given motor.
I use Mark Kelly's Synchrotron AC-1 controller, which contains all of the aforementioned features (and then some) but has long since been unobtainable; this was a DIY Audio kit project from several years back. You bought the raw boards, bought the parts, understood the design's theory and you were basically on your own; you built the unit from the chassis on up - not a build for the novice. I admit, I've been spoiled by the controller's abilities.
Another possible candidate in the making is this gentleman's controller, based around a PIC/Atmal chip:
http://www.soundbound24.blogspot.ca/ (scroll down to the Bi-Onda controller). He seems to be on a hiatus, but I'm hoping he continues on the fascinating path he's on; his is the most promising and versatile design I've seen in a while.
I would gather that without upping the power handling of the output amplifiers, both this controller and my Kelly can't drive anything larger than say, 7 watts (the average synchronous motor in a TT is usually 3-5 watts).
There is also the Sander's speed controller over on Lenco Heaven: http://www.lencoheaven.net/forum/index.php?topic=2042.0 This appears to have applicability toward higher wattage motors (15-20 watts), and shaded-pole induction types as used in the Lenco, Garrard and others. I haven't gone through the entire post to tease out the details of the circuit, but it appears to cover the essential parameters. I'm still exploring the salient characteristics in this lengthy thread.
I've never had a Walker controller open to see what makes it tick, but I'm guessing it's about the same as the SDS. While a Linn Lingo has a nice sine wave synthesizer, it also doesn't allow for any parametric adjustment - despite the fact they're loaded with (unlabeled) trim pots.
While I advocate complete parametric motor adjustment, it's also a catch-22. You need some test gear like a multimeter and an oscilloscope to really maximize performance; a little too far this way or that with some settings and you can really mess things up (as in your motor stalls, vibrates and you become sad because your table no longer spins). This, I believe, is the reason nobody has a desire to market a motor controller which contains all the necessary parametric adjustments: the support issues would instantly turn into a complete nightmare since most folks simply aren't technically savvy enough reap the benefits or dig themselves out of the inevitable holes that would result.
Palasr, You are correct; the Walker MC is likely to be pretty much like the SDS. This is what I was referring to in my previous post "most" current commercial controllers do not actually split the phase of the AC.
I am awaiting delivery, as I mentioned, of Mark's second generation controller. It's a finished product, not a kit.
If the controller does not split phase (relies on a capacitor in the motor to split phase), then I would expect that one is better off moving the belt on a pulley rather than electrically switching speed.
The motor controller for the Basis turntable does properly split phase in the controller, sending two separate power lines to the motor. The motor has to be modified in order to use the controller (one cannot just plug the motor into the speed controller).
Dear Larry, I think those are two different things (splitting phase, which is an advantage for an AC synchronous motor controller, vs electrically switching speed, which can be done by either controlling voltage or AC frequency or both, depending upon the type of motor). The only issue would be for an induction motor where there is kind of a plateau for voltage, below which the torque falls to zilch. Please anyone correct me if I'm wrong in this; motors are a complex subject that I hardly can claim to study on a daily basis. I am going on my fading memory of Mark Kelly's teachings.
Also, it's not "two separate power lines" strictly speaking. It's taking the sinusoidal AC wave form and generating a second one that is 90 degrees away from the first, so the motor is driven in quadrature. As I understand it, the more perfectly that is achieved, the smoother the motor will run. That's what a capacitor tries to do but does not do nearly as well.
Roscoeii and Redglobe, perhaps you can contact me by email. I cannot seem to find your respective email addresses. Let me know if you cannot find mine. I may be able to help, in any case.
First of all, thanks for shedding some light on a fairly dimly lit subject. I have recently upgraded to a Premotec 9904 111 31813, which is supposed to be a low noise, low vibration motor. I am happy with the motor, but have struggled with it's optimization. Assuming that I am capable of building a parametric controller as you have described, could you be more specific about the procedure. It seems to me that with the number of adjustments available, and without a suitable procedure, I would still be "taking a shot in the dark".
Thanking you in advance,
Posted at 5:48 AM 28-NOV-2012
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 ;-)
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.
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
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.
Posted 11:53 AM 28-NOV-2012
There is no procedure for finding the 'magic setting', as every motor is different. For example, I have three Hurst 300 RPM motors, but really only one is worth a damn - the other two can never be quieted down to a suitable level, and never quite sound right. I set a motor so as to null vibration as much as possible - you can either hold the motor in your hand, use a mechanics stethoscope, or listen to the table rotating in a lead-out or locked groove. From there, I'll look at the waveform on an oscilloscope to ensure the sine waves look nice; I generally find that a slightly distorted waveform actually yields a better result than a pure sine wave (I don't know why). From there on, it's all in the listening, trying to balance torque requirements with vibration considerations. I'll vary the voltage of each phase slightly, and make assessments from there. For example, a motor with too much voltage will always place too much emphasis on the attack of notes, while too little will yield a bloated bass and a really laid back presentation. The more you play around, the easier it becomes to hear where you're at and establish a baseline sonic signature - speed never varies given the nature of the motor, but the way the motor deals with heavy modulation, stylus drag and the like can all be readily discerned. Unfortunately, there is no purely objective way of measuring any of this, like so much in this odd little hobby. Trust your ears, and beyond all else, have some fun.
Not a big fan of AC but I just made pulleys and Housing SST for a Hurst 300 RPM. It is Dead on timing but the Wow & Flutter is within 1 Icon on a KAB Strobe. Can you hear it? well on some songs. This is a Belt drive set up. You pay for what you get, if you want perfection then look around at DC with a Class A power supply.