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New Music Hall Cruise Control 2.0

GreatTone

GreatTone

Super Member
I've been wanting to get something like this for a while, if for nothing else than being able to change speeds without taking the platter off. But $300 was seeming a little pricey, even though you can pay 3 times that for other brands that seem to be about the same product. But I found it on Amazon for $229, so I bit.

It works as advertised, and it did change the sound, though I haven't decided if it's all for the better. There are 2 things. One, my Ariston RD11S was running a little fast, so now that it's running at the right speed, some things that I'm very familiar with sound slower (which they are). That's fine, as that's the way it's supposed to be.

The other change is more subtle, but definitely there. Before, when looking at the table with a strobe, there was a bit of movement, maybe it's cogging (?). Locking in the speed, I was able to mostly eliminate that movement. I don't know if that's what accounts for this other change in sound, but it sounds like the sound is more controlled. It's almost like when I've done mods that reduced resonance before. At first it sounded like something was lacking, like the sound was less full somehow. But in time, I realized it's because the sound is more stable, more accurate, less blurry, etc. So maybe that's what I'm hearing, and it's ultimately a good thing. Also, there is less background noise now, and the motor seems to be running more quietly.

I have a question though for the technical members. Since the AC synchronous motor uses a phasing capacitor which is tuned for 60Hz, what is happening when the frequency is lowered to get the other speed? You put the belt on the 45 rpm pulley, and the controller outputs a 60Hz sine wave for the 45 speed, then a lower-frequency wave for the 33 1/3. Isn't the capacitor tuned for 60Hz? Is this a problem? The product info says the controller can be used on any turntable using a 120VAC synchronous motor. Just wondering.
 
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No AK experts on AC synchronous motors and how changing the frequency affects capacitor-supplied phase angle?

Paging Pio1980...
 
What other models besides Music Hall does this box work on? You mention you're using it on an Ariston, that implies that this box is somewhat universal. Anyone?:scratch2:
 
I was a bit surprised by what the motor capacitor does to the AC signal on these motors. During development of my TT motor controller I put the signals on an oscilloscope and was not really liking what I saw. Some motor controllers only provide a single reference sine wave and still use the motor's capacitor for the phase shifted second coil. I decided to make a dual sine wave generator so that the capacitor can be eliminated, although the design does allow you to run it in single source mode like the Music Hall unit. The phase shift may be altered at 45, I never tried this to check. Maybe in future.

If anyone is curious, my adventures in the design and prototyping our outlined on a blog I started up, the link is below if anyone wants to check it out.

SoundBound
aka Rick

My Audio Blog
 
SoundsRight said:
I was a bit surprised by what the motor capacitor does to the AC signal on these motors. During development of my TT motor controller I put the signals on an oscilloscope and was not really liking what I saw. Some motor controllers only provide a single reference sine wave and still use the motor's capacitor for the phase shifted second coil. I decided to make a dual sine wave generator so that the capacitor can be eliminated, although the design does allow you to run it in single source mode like the Music Hall unit. The phase shift may be altered at 45, I never tried this to check. Maybe in future.

If anyone is curious, my adventures in the design and prototyping our outlined on a blog I started up, the link is below if anyone wants to check it out.

SoundBound
aka Rick

My Audio Blog
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Yes, that is my question. At 45 rpm, the controller puts out 60Hz, so no problem. However, if it simply alters the frequency to get 33 1/3, that means the capacitor at that lower frequency is no longer optimally tuned for lowest noise etc. However, if the voltage is also changed, that may compensate for it. Maybe I'll put the Music Hall controller on my oscilloscope and see what it does.

It may all be moot, however. The motor seems to run quieter, so maybe all's good.
 
michaelhigh said:
What other models besides Music Hall does this box work on? You mention you're using it on an Ariston, that implies that this box is somewhat universal. Anyone?:scratch2:
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http://www.musichallaudio.com/detail.php?p=84

The quartz lock provides perfect speed control for all Music Hall turntables, many Pro-ject models, and any turntable with 120v AC synchronous motor. Please consult your dealer for a full list.
 
I noticed a change when I hooked up my speedbox. It made it seem more sterile or clinical. I should have got the one u did as its adjustable. The regular speedbox isn't
 
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juno said:
I noticed a change when I hooked up my speedbox. It made it seem more sterile or clinical. I should have got the one u did as its adjustable. The regular speedbox isn't
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Is the speedbox putting out enough "juice" to drive the motor with sufficient torque? I don't have one and have not really looked at it's specs, but if your not getting the impact and dynamics, wonder if it's an issue more to do with torque than the correct speed ???

Just a thought.
 
My issue is this: everything I've read about synchronous AC motors says that the motors are designed to run at 60 Hz (in the US). Simply changing the frequency to alter the speed (ie running the belt on the 45 rpm pulley at 60Hz for 45 rpm records, then dropping the frequency to 44 or so to get 33 1/3), without tuning the motor run capacitor to give the correct phase angle, is sub-optimum, to say the least. Loss of torque and speed inaccuracy are the two main results of changed frequency.

However, it can apparently be helped by adjusting the voltage as well as the frequency. I should just measure the output of mine. Maybe tonight...
 
SoundsRight said:
Is the speedbox putting out enough "juice" to drive the motor with sufficient torque? I don't have one and have not really looked at it's specs, but if your not getting the impact and dynamics, wonder if it's an issue more to do with torque than the correct speed ???

Just a thought.
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It's working fine. Just noticed a difference in sound. I went back to the standard PSU, but just recently bought a new speedbox. Maybe the silver one will sound better..lol
 
Well, regardless of its theory of operation, this Music Hall controller is a very definite upgrade in sound. With it on, the sound is more detailed, solid, 3D, with better separation and front to back imaging. I compared the same tunes, on both 33 and 45, and the difference was very audible.

Using a stethoscope, the motor seems to run quieter with the Music Hall controller in. Somewhat interestingly, it is near dead silent at the 33 setting (ie, not 60Hz), while there's some motor vibration at 45, both with and without the Music Hall. I think the original motor run cap needs to be changed, which may, or may not, change the vibration level.

One thing that was subtle but definite I found interesting. On one jazz tune, the piano sounded more up front without the Music Hall. With the controller in, the piano was slightly recessed. But then I thought to increase the Music Hall's speed to the normal 45 (I had it dialed down to 44.5 to correct the tt's slightly fast speed) -- and then the piano jumped back out.

So if you prefer the sound of PRAT (which seems to mean the table runs fast :D) then you can dial that back in. In the end I prefer it running at the correct speed.

I had another thought as well. If at some point I determine that running the motor at a lower frequency is somehow not good for the motor, then I would still use the Music Hall controller, but I would keep it set on the 45 rpm setting to get the 60Hz frequency, and just continue to switch the belt manually to get 33. Because even without the convenience of being able to change speeds with a button, I believe it would be worthwhile just for the ability to fine tune the speed and get a very pure, accurate sine wave. However at this point, I see no reason not to use the push button speed controller.
 
I emailed the US distributor last year and he said it would work with any AC motor. I asked specifically about the VPI HW19 motor.
 
I was a little concerned about the 3W max output of the Music Hall controller. So last night I looked at my motor and it said 0.015A, which I thought a little strange, in that there was no wattage figure. Easily fixed: using the old ohm's law, P = IE, I got 120V x 0.015A = 1.8W. Well under 3W, no problem!

On another note, my Ariston RD11S still had the original capacitors in it. There are two, the motor run cap and a spark suppressor across the on/off switch. The switch has been popping a bit, so I figured that one was shot, but I thought I would change both of them while I was at it. It's very easy, as there is a screw-connector board, so no soldering involved. After I got the old ones out, I put them on my trusty Sprague TO-5 capacitor checker -- the power switch cap was truly shot, but the motor cap was dead on at 0.18uF. I saved the motor cap but left the new one in there. It runs the same, but now it's good for another 50 years. And now the on/off switch is silent, so that's good.
 
My issue is this: everything I've read about synchronous AC motors says that the motors are designed to run at 60 Hz (in the US). Simply changing the frequency to alter the speed...without tuning the motor run capacitor to give the correct phase angle, is sub-optimum, to say the least. Loss of torque and speed inaccuracy are the two main results of changed frequency.

However, it can apparently be helped by adjusting the voltage as well as the frequency. I should just measure the output of mine. Maybe tonight...
Click to expand...

Indeed. It should be noted however that the run cap which achieves phase shift is tuned primarily to the motors coils, not necessarily the power line frequency. On a motor such as an induction or shaded pole AC motor, you need a start cap to get the motor moving, and this is a much larger cap that is generally rated for mains frequency. To achieve phase shift, one uses only a small value cap (usually 600VDC rated), and this value is related coil design and the parameters of capacitive and inductive reactance, overall torque, RPMs, wattage, etc. Since these factors vary considerably with a change in frequency, ergo, the value of the run cap must vary as well to achieve correct phase angle; I would guess that most 2-10 watt AC sync motors can vary in frequency (with a run cap in place) by no more than +/- 15 Hz, if that. Without a run cap, driving the motor with synthesized sine waves, this value can be increased by approximately +/-35 Hz (provided concomitant changes in drive voltage occur, along with the addition or subtraction of harmonic distortion content which, as you vary wildly in frequency, actually becomes somewhat beneficial in maintaining good torque, and reduces cogging artifacts significantly).

So, while that little motor run cap is worrying, it's worrying only in relation to the electrical parameters which change in the motor's coils relative to frequency. Like most electronic systems which are tuned, a change in one parameter necessitates changes in all of them.

I do find it odd that they insist on your using the 45 RPM pulley at 60Hz, and then decreasing the frequency to achieve 33 RPM, most likely at a reduced voltage. To me, this points to a weakness in the controller to generate additional voltage to properly control a higher frequency setting for 45RPM. In a perfect world, the Project should use the 33RPM pulley for 33RPM @ 60Hz, and increase the frequency AND voltage for 45RPM. Given the limitations of a mere 3W output, I suppose this isn't too surprising. My point is that most of us listen to a LOT more 33 RPM LPs than we do 45's, and that I would design a controller that optimized 33RPM over 45. I use a Mark Kelly Synchrotron controller which dispenses with the motor cap completely, and allows wide adjustment of phase angle and amplitude, frequency and distortion components. A much more complex, but ultimately more tuneable and satisfying controller.

-Richard
 
palasr said:
Indeed. It should be noted however that the run cap which achieves phase shift is tuned primarily to the motors coils, not necessarily the power line frequency. On a motor such as an induction or shaded pole AC motor, you need a start cap to get the motor moving, and this is a much larger cap that is generally rated for mains frequency. To achieve phase shift, one uses only a small value cap (usually 600VDC rated), and this value is related coil design and the parameters of capacitive and inductive reactance, overall torque, RPMs, wattage, etc. Since these factors vary considerably with a change in frequency, ergo, the value of the run cap must vary as well to achieve correct phase angle; I would guess that most 2-10 watt AC sync motors can vary in frequency (with a run cap in place) by no more than +/- 15 Hz, if that. Without a run cap, driving the motor with synthesized sine waves, this value can be increased by approximately +/-35 Hz (provided concomitant changes in drive voltage occur, along with the addition or subtraction of harmonic distortion content which, as you vary wildly in frequency, actually becomes somewhat beneficial in maintaining good torque, and reduces cogging artifacts significantly).

So, while that little motor run cap is worrying, it's worrying only in relation to the electrical parameters which change in the motor's coils relative to frequency. Like most electronic systems which are tuned, a change in one parameter necessitates changes in all of them.

I do find it odd that they insist on your using the 45 RPM pulley at 60Hz, and then decreasing the frequency to achieve 33 RPM, most likely at a reduced voltage. To me, this points to a weakness in the controller to generate additional voltage to properly control a higher frequency setting for 45RPM. In a perfect world, the Project should use the 33RPM pulley for 33RPM @ 60Hz, and increase the frequency AND voltage for 45RPM. Given the limitations of a mere 3W output, I suppose this isn't too surprising. My point is that most of us listen to a LOT more 33 RPM LPs than we do 45's, and that I would design a controller that optimized 33RPM over 45. I use a Mark Kelly Synchrotron controller which dispenses with the motor cap completely, and allows wide adjustment of phase angle and amplitude, frequency and distortion components. A much more complex, but ultimately more tuneable and satisfying controller.

-Richard
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This was my concern, though in actual fact it seems to work fine and actually improves the sound significantly on both 45 and 33, according to my ears doing back to back comparisons with and without the controller. I have not yet put my Fluke on the output to see if the voltage is altered at 33, though at some point I'm going to measure the voltage and frequency, and look at the waveform on my scope. The way it lowers the frequency to get 33 means the frequency would be about 44.5Hz, so about 15Hz lower. I read that altering the frequency beyond 10Hz can result in unstable operation in synchronous motors, both in terms of speed and vibration, but in practice I've noticed none of that.

In fact, using a stethoscope on the plinth reveals the same motor noise level with and without the controller -- or, if anything, there is less noise using the controller. Interestingly, with the controller and running at 33, there is quite a bit less vibrational noise than at 45, which runs at the normal 60Hz. Not sure how to explain that, except maybe the capacitor value was not optimal to begin with, and it's somewhat dumb luck that it is more suited to the lower frequency. But that is speculation.
 
PS: That Mark Kelly Synchrotron sounds like the best bet. Where did you get it? Sounds like it supplies the individual phases, and allows you to tune them for least motor vibration. The only other controller I know of that does that is the VPI, which is $1200...
 
GreatTone said:
PS: That Mark Kelly Synchrotron sounds like the best bet. Where did you get it? Sounds like it supplies the individual phases, and allows you to tune them for least motor vibration. The only other controller I know of that does that is the VPI, which is $1200...
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GreatTone;
I am building one that supplies the individual dual sine waves, digitally generated. You can see it here:

Motor Controller Blog

If I get interest for it, maybe I can get some together for an interested group of people. Project has been a lot of fun to design and build so far.
 
Actually, the Kelly controller is considerably more versatile than the VPI controller (or the Walker, or, well nearly anything), as it's waveforms are digitally generated (as opposed to operating purely in the analog domain). I bought one when Mark was offering the kits on DIY Audio. For the boards, some of the harder to source parts and all the documentation, it was $90 back 5 or so years ago. The rest of the parts from Digi-Key were another $150. I actually have another in raw form; they are completely unobtanium these days.

Mr. SoundsRight has a VERY interesting looking controller, and has a nice array of features. I like the fact that it's firmware driven (16-bit PIC/RISC?) and can be tailored to a specific motor's operating points. I for one, would be very interested in hearing one; if it works as well as it looks on paper, you're onto something very good. Perhaps an interesting trade can be worked out...
 
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