2 phase DDS signal generator to run 2 phase AC sync motors - Page 2 - diyAudio
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Old 26th December 2012, 01:13 AM   #11
kevinkr is offline kevinkr  United States
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Hi JG,
Looks great.. If you'd like I'll see what I can do with the earlier posts. You can attach source code, and gerber files, etc., if you zip them first. Schematics can be posted as pdf files..

Merry Christmas!

Thanks for posting this material. I think in the longer run there will be members who will find this very interesting.
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Old 27th December 2012, 06:34 AM   #12
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This sort of ac generator can make the motor run at correct speed for both 33 and 45 rpm without changing pulleys. Do you have an opinion on which is best, natural 33 and higher frequency to get 45 rpm or natural 45 rpm with the larger pulley and lower frequency to get 33 rpm?
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Old 27th December 2012, 07:07 PM   #13
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I do not know. I think the first, but I do not remember why we choosed this.
I have a pulley which is made for 50Hz mains, so for 45, I use higher freq. Same for others who tried it. It would be easy to put on the 45 section of a dual pulley and slow down the control to 33, but I do not remember we tried it. I think it is just because in hand the motor run more smooth on near 50Hz than under that.
One more argument to make the vibration meter (detector).
One thing I know for fact, the Airpax is not stable with 78. It starts with help, turns the platter than, but if you stop it doesn't start without help. It is possible that if we use a bit bigger pulley, it would be stable on 33, 45 and 78 also.
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JG
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Old 27th December 2012, 10:18 PM   #14
Nanook is offline Nanook  Canada
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Default Giordano, nice project.

was discussing something similar with my audio partner to drive his Xerxes (his PS is not working correctly).
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Old 28th December 2012, 05:47 PM   #15
jlevro is offline jlevro  United States
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Quote:
Originally Posted by Giordano View Post
One thing I know for fact, the Airpax is not stable with 78. It starts with help, turns the platter than, but if you stop it doesn't start without help. It is possible that if we use a bit bigger pulley, it would be stable on 33, 45 and 78 also.
Regards,
JG
One possible solution is to "ramp up" the frequency of the DDS. If you want to use 78, then start at 45 and then step your way up to 78 in several steps.

JL
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Old 28th December 2012, 06:45 PM   #16
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I do not recommend. If it gets out of sync, it does not lock again without help. I think the airpax is not for that freq. I can not tell measured data, but I feel more vibration also. It is on the edge.
I think if 78 is a must, should have another diameter on the pulley (If your motor is an Airpax).
In the other hand, I have some other motors, which can do the 78 easy, for example an old Tesla motor. ... but, the problem is, on 50Hz the Airpax is much better on vibration and torq.

ÜDV JG
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Old 28th December 2012, 07:53 PM   #17
jcx is online now jcx  United States
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has no one mentioned just using soundcard or even DAP for experimenting - no need to build anything if you already have ampilfiers
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Old 29th December 2012, 01:26 AM   #18
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Increasing frequency for 78 rpm is going to need an increased drive voltage, to compensate for the effects of winding inductance and rising core losses both reducing torque

It is not obvious to me how changing frequency affects the audible noise. You have various effects going in different directions:
1 RIAA equalisation boosts the lower frequencies
2 Does the preamp have a rumble filter?
3 Higher frequencies are more audible
4 Mechanical resonances of the arm/cartridge and deck suspension
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Old 29th December 2012, 06:58 PM   #19
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sourcing from a soundcard, to try if the motor would run on higher rpm, that could work, but for live test it is far away. The point to use dds is to have accurate control of phase difference and low distorsion, stable signal.
JG
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Old 29th December 2012, 07:10 PM   #20
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so far the best result I got is to get as close to the original levels as possible. The Airpax does not get 110V in the original setup either (at least in case of rega and systemdek). I drive it with 80-90Veff also. When I increased the drive amplitude, I got very little more torq but heat on the motor. Also, even with normal drive level, when I increased the freq to get 78rpm, with the instability, I got heat also. I think the airpax is just not capable to run in much higher freq. 45 is fine, but 78 is not.
It is very similar to what stepper motors (like this) does at too high step freq.

JG
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