| 回覆 (2099): VPI |
BTW, your earlier link indictes the controller has adjustment in 0.1% steps, so that translate to about 0.05Hz. As I am not so pitch sensitive, that’s probably good enough for me. However, better controllers usually have a resolution of 0.01Hz
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the accuracy will depend on the clock used. he using a 24MHz for 50Hz mains. to improve that one needs a high clock rate. this is only theoretical. the accuracy of the clock will play a part. he is using a rather crude program and DAC ie 6 bit. i probably use the cpu in the 27D to do the control and using an external say12bit dac to generate the sine wave. the 27D CPU only runs at 16MHz though. |
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drwkng
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13-02-15
13:08:33
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| 回覆 (2099): VPI |
Just to clarify, the adjustment of the frequency on the Powerplant was in 1Hz steps with a click of the button, so I was clicking the button in rapid successions. Don't know whether that creates any problem with the program.
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don't really know. by the way, how do u power your motor right now? from mains or thru vendor supplied controller. |
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drwkng
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13-02-15
12:37:11
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| 回覆 (2098): VPI |
Just to clarify, the adjustment of the frequency on the Powerplant was in 1Hz steps with a click of the button, so I was clicking the button in rapid successions. Don't know whether that creates any problem with the program.
BTW, your earlier link indictes the controller has adjustment in 0.1% steps, so that translate to about 0.05Hz. As I am not so pitch sensitive, that’s probably good enough for me. However, better controllers usually have a resolution of 0.01Hz.
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thekong
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13-02-15
08:52:11
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| 回覆 (2097): VPI |
I am not sure whether that would work! As mentioned, with the Powerplant, when I changed the speed by switching the frequency (from 50Hz for 33.3rpm, up 1 Hz per step), the platter slowed down and stopped!
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that sounds a bit strange. anyway i found the article from Mark Kelly on his controller.
http://web.archive.org/web/20090215113614/http://members.iinet.net.au/~quiddity/audio/Quadrature.html
he used LM1875 to drive an output motor. i have LM3886 pcb made for my usher. i can easily get one up with my spare boards and see what happens. |
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drwkng
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13-02-15
00:05:01
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| 回覆 (2096): VPI |
I am not sure whether that would work! As mentioned, with the Powerplant, when I changed the speed by switching the frequency (from 50Hz for 33.3rpm, up 1 Hz per step), the platter slowed down and stopped!
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thekong
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13-02-14
16:28:26
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| 回覆 (2095): VPI |
| just another thought about this. would it be easier to control the frequency of supply voltage ie start it would low frequency say 10Hz and slow ramp it up with the desired frequency. this might solve the problem of starting the motor. |
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drwkng
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13-02-14
16:13:31
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thekong
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13-02-14
15:57:18
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| 回覆 (2093): VPI |
Mark Kelly suspected that it was due to the back EMF of the motor. So, may be it is possible to program the controller to have a higher voltage during start up (and switching speed), and return to normal voltage after the platter attained the correct speed?
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with the transformer coupled output, it should be less influenced by the back EMF. it would be straight forward to program a speed profile with higher than 220v to start with and then drop to below 220v later. |
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drwkng
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13-02-14
15:47:08
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| 回覆 (2094): VPI |
>It's inertia which depends largely on the mass of the platter….<
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That may not be the main cause of my problem. I asked Walker whether their controller could drive the Rockport motor, and their reply was negative. As Walker’s own turntable has a pure lead platter weighting 70 lbs, which is much more heavier than the 20lbs or so platter on my Rockport, I suppose inertia is not the main problem.
Direct drive turntables usually depends on servo to control speed, while belt drive needs the heavier platter to maintain speed stability. The only direct drive turntable that I know of using a heavy platter is the Rockport Sirius III, which has a 60lbs platter!
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thekong
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13-02-14
15:43:21
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| 回覆 (2093): VPI |
It's inertia which depends largely on the mass of the platter. When the trend of extreme mass becomes order of the day, the torque required to kick off can be considerable.
If speed stability can be achieved by means other than the heavy flywheel, things should become far more manageable. The National "rice cooker" is a prime example.
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limage
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13-02-14
14:21:02
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| 回覆 (2092): VPI |
While I wouldn't think a turntable motor would be more powerful than 15-20W, as mentioned before, the VPI and Clearaudio controllers could not start the Rockport motor at 45rpm. Even with the Powerplant’s 1200W, it could start the motor at both 33.3 and 45 rpm, but would stop if I change the speed by switching the AC frequency!
Mark Kelly suspected that it was due to the back EMF of the motor. So, may be it is possible to program the controller to have a higher voltage during start up (and switching speed), and return to normal voltage after the platter attained the correct speed?
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thekong
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13-02-14
13:43:34
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| 回覆 (2091): VPI |
How about the output, would it be possible to increase the power output by using more tubes?
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this part i'm not quite sure. according to this the article, he is only using somethng like15-20W output transistor. so the motor can't be more powerfully than that. 15-20W is nothing for tube amp. but granted the output transformer is 12V to 220V. by reducing the ratio, say 24v-220V, it should have better control of the motor. i can rip up something without too much trouble, using an off shelf toroid transformer. anyone has a motor to destroy^-^
i'm catching on the writing by Mark Kelly as well. i will take a look at k&K too.
if i can get one phase going, having another at 90 degree should be a piece of cake. |
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drwkng
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13-02-14
11:06:30
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| 回覆 (2090): VPI |
Dr King, Happy Chinese New Year!
A tube motor controller, about time I say ! :-)
I remember from some of Mark Kelly’s posting about his motor controller could generates 2 sine waves (90 degree apart ?) to drive the 2 coils separately, so there is no need for the phase splitting cap. It is also possible to minimize the motors’ vibration by tuning these 2 outputs. I wonder if this controller can do the same.
K&K is also designing a controller around the same idea, and here is what they said:
“A Turntable Motor Power Supply Kit that will independently drive both coils in a hysteresis synchronous motor with variable frequency and apply the appropriate phase shift for optimum vibration performance.”
How about the output, would it be possible to increase the power output by using more tubes?
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thekong
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13-02-14
08:49:20
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| 回覆 (2089): VPI |
hi Kong,
came across this article.
http://www.diyaudio.com/forums/attachments/analogue-source/329856d1360606928-ac-quartz-speed-controllers-linn-roxan-ttpsu.pdf
if i'm going to make one, it is very much along the same line of thinking. of course i would make it with tubes. |
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drwkng
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13-02-13
11:13:03
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dkyyu
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13-02-10
12:39:13
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daiwok
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13-02-09
23:59:59
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thekong
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13-02-09
08:30:00
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daiwok
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13-02-09
00:12:56
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daiwok
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13-02-08
23:37:40
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| 回覆 (2099): Another Bearing |
I have been using after market SUPER BEARINGS for my Lenco and Garrard 301 for some time. These bearings are super as they are machined with tighter tolerances and run direct from spindle to thrust without the use of a ball bearing. The housing is a once piece phosphorous bronze. A couple of months ago I did a group buy and some people have asked if they have arrived ..........
looks like we need a Bearing EGM !! |
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daiwok
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13-01-24
12:50:12
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| 回覆 (2098): Another New Arm |
>The movement if I am not mistaken is similar to the linear Schroeder ....<
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I am afraid that this arm is not as sophisticated as the Schroeder!
What they meant by “Straight Arm” is just a straight armtube with no offset, rather than linear tracking!
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thekong
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13-01-23
12:17:43
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| 回覆 (2097): Another New Arm |
| The drawing is misleading and exagerrated IMHO. The movement if I am not mistaken is similar to the linear Schroeder which is the arm pivot is not fixed and is moving towards 7 to 8 o'clock in order to make this "straight arm" geometry work. |
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daiwok
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13-01-23
11:49:28
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| 回覆 (2096): Another New Arm |
The "rigid float" pivot is one thing we have no way to verify unless we could see how it works inside the housing. Arm geometry is yet another puzzle……..
The straight cartridge mounting without offset is there to openly defy all the wisdom on minimum distortion brought about by tracking error. This is either a bold breakthrough to reveal the ultimate truth or a fetching argument to fool the ignorant. I am afraid it is likely to be the latter.
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limage
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13-01-23
11:44:03
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| 回覆 (2095): Another New Arm |
My impression is that they are saying arms like the Well Temper and Schroder still need a string to center the pivot.
But in their design, the whole floating structure is self-centered with no other mechanical contact with other parts of the arm!
It is quite interesting if it really works!
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thekong
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13-01-23
10:36:49
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daiwok
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13-01-23
10:26:57
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| 回覆 (2093): Another New Arm |
Well, they said it is a "oil floated pivot (magneto-fluid = magnetically induced oil) "
But then they also said: "There are similar type of bearing pivot, dipped in oil bath (Oil damp Type), available in the market, but still they require some string or another apparatus to fix fulcrum for arm rotary motion but RF, thanks to automatic positioning mechanism, requires absolutely nothing to interfere with the force, for cartridge stylus to follow the inward path of record groove."
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thekong
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13-01-23
10:19:03
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daiwok
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13-01-23
10:01:39
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| 回覆 (2091): Another New Arm |
>if you want perfect tracking with "zero" tracking error..........<
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But they are not looking for "zero" tracking error ;-)
>I dare you to buy to prove me wrong !! @@ <
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Buy that arm?!!!! I may look stupid, but I am not that stupid! :-)
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thekong
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13-01-22
17:27:58
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| 回覆 (2090): Another New Arm |
I saw this tonearm and god is it ugly !! everything has resistance, just the matter of how much. Having 2 extra contact points already says its bad ! removable headshell and phono sockets ! those o-rings on the arm tube - what were they thinking ? if you want perfect tracking with "zero" tracking error then linear tracking is the only way regardless whether its an air bearing of not.
Anyway - even these buggers look better than this tonearm !!
I dare you to buy to prove me wrong !! @@ and yes that's a toilet plunger where the cartridge goes !!! |
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daiwok
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13-01-22
17:23:29
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thekong
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13-01-22
17:17:08
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| 回覆 (2088): VPI |
Dr King,
It seems like no modern TT list their power consumption! May need to take my TT’s motor out to check the spec.!
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thekong
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13-01-22
17:15:59
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drwkng
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13-01-15
19:31:34
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| 回覆 (2086): VPI |
Ah...Ok, as I understand this AC motors have different models for 110V and 220V. The one in my TT is the 220V model (direct drive from the wall socket), so probably no good with the chips amps then! :-(
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thekong
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13-01-15
18:37:31
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| 回覆 (2085): VPI |
| i don't know. what kinf of power we are talking about? a bridge or parallel chip amp should be able to deliver enough power to drive those little motor. there are of cours more logic involved in the whole controller. these are AC motors, right? do they expect 220V AC to drive them.? if they do, we are talking about rather large voltage output but not much current. these are not the territory of ICE chip or any chip amp. |
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drwkng
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13-01-15
17:36:10
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| 回覆 (2084): VPI |
Hi Dr King,
Just a though, wondering if a digital amp, like the ICE chip, would be a good applicant for the motor controller. They are certainly powerful and quite cheap, especially when using digital power supply!
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thekong
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13-01-15
17:26:14
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| 回覆 (2083): VPI |
Wah saw this on Audiogon today ....
http://app.audiogon.com/listings/tonearms-schroeder-reference-tonearm-2013-01-11-analog-90291
Too bad I have no clue about buying pre-own tone arm, sounds like a risky business for the amature like me. |
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Cadiver
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13-01-12
13:07:14
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| 回覆 (2082): VPI |
>i know what can you. get a pair of gm200 to drive it <
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Use OTL as motor driver? Good idea, I think it would sound very fast and transparent!
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thekong
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13-01-11
17:13:34
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| 回覆 (2081): VPI |
If it can be done, I really don't mind have one with dual sine wave and uses say 8 KT88s! It would be cool! ;-)
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i know what can you. get a pair of gm200 to drive it |
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drwkng
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13-01-11
16:38:01
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| 回覆 (2080): VPI |
So, the problem is in the interface betwen the power amp and the motor?
If it can be done, I really don't mind have one with dual sine wave and uses say 8 KT88s! It would be cool! ;-)
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yes, i think the motor and platter assembly presents a difficult load. the phase generation stuff is the easy part. |
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drwkng
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13-01-11
16:28:59
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| 回覆 (2079): VPI |
>it sounds like serious stuff. <
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Yes, and that's why I still can't one that works for me!
While I don't really understand the technical side, but it seems like a signal generators is easy to get and a power amp of 50-60W is no big deal.
So, the problem is in the interface betwen the power amp and the motor?
If it can be done, I really don't mind have one with dual sine wave and uses say 8 KT88s! It would be cool! ;-)
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thekong
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13-01-11
16:19:52
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