AC motor controller
- Thread starter Doc B
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rockpassion
New member
Doc, I have a VPI MK IV TT and have a real hard time justifying $1100 - $1300 for the VPI controller. So IMHO this is a GREAT idea. As long as it is reasonable in price sign me up.
Hopefully it is something that could be done soon.
Thanks,
Richard
Hopefully it is something that could be done soon.
Thanks,
Richard
I would like to echo that I have a VPI and I would love to be able to unplug it from my PS Audio power conditioner into a designated controller and be able to more accurately control the speed. It has to be tube rectified though 
But also, as others have stated price concerns, if it is a $1,000 or more I probably won't buy it. For me, it needs to be in the $500 range and then I am very interested. I would wonder if it is even possible at that price point, but beyond that I would rather be honest and state upfront that I probably wouldn't spring for it. I would rather buy the Bee Pre!
But also, as others have stated price concerns, if it is a $1,000 or more I probably won't buy it. For me, it needs to be in the $500 range and then I am very interested. I would wonder if it is even possible at that price point, but beyond that I would rather be honest and state upfront that I probably wouldn't spring for it. I would rather buy the Bee Pre!I'm interested for sure. Forgive my ignorance, but could this design your considering be adaptable to rim drive? We have a pile of 3" thick 6061 Aluminum material at my shop, and I've been dreaming about a new DIY turntable with a 3" thick platter. I was considering trying to build a rim drive for the heck of it. Maybe a plywood prototype base, with the aluminum platter and a bearing (built in my shop). I figure if I'm building the platter and the drive pully, I can adjust the diameters to get the speed close, and dial it in from there. If it works good, then pull the platter and bearing ahead into a nice finished base. If the rim drive idea crashes and burns, it would be easy to use with a belt and pully. There's lot's of ground to cover here, and I'm at the dreaming stage. My current DIY table uses a Terres motor kit that measures a strobe disk on the bottom of the platter to maintain speed. It features a super simple homemade bearing, acrylic platter, and Rega RB250 with Incognito upgrades. I think it works and sounds pretty darn good, but i don't have much to compare it too.
Pfenning
Pfenning
Paul Joppa
Moderator
I helped a friend set up something to drive a rim-drive table, really made much more difference than I expected. I don't mind making some electronic designs, but the big question is, what are the requirements - voltage and current? Sine-wave distortion? What tables might need the most power?
Pretty much anything will drive an old AR, but how about a Rek-O-Kut? I can easily see a low-power source that overloads on startup but eventually gets the platter going, and then keeps it going well.
Probably we should build something and try it out ...
Pretty much anything will drive an old AR, but how about a Rek-O-Kut? I can easily see a low-power source that overloads on startup but eventually gets the platter going, and then keeps it going well.
Probably we should build something and try it out ...
Grainger49
New member
I have had a bookmark to Pabst Synchronous motor. I'll find it and get back to you.
I'm assuming you can make the idler wheel and calculate the circumference versus motor RPM. Right now I couldn't.
I'm smoking a turkey today and am on and off line.
I'm assuming you can make the idler wheel and calculate the circumference versus motor RPM. Right now I couldn't.
I'm smoking a turkey today and am on and off line.
Grainger49
New member
It is hard typing now, I was scalded moving the turkey on the fire.
Here is a link to a motor manufacturer you can buy synchronous turntable motors from.
http://www.hurst-motors.com/papbdirectdrive.html
Here is a link to a motor manufacturer you can buy synchronous turntable motors from.
http://www.hurst-motors.com/papbdirectdrive.html
Thanks for the link Grainger. I hope your ok from the scalding, I know how easy accidents can happen when working around the grill. On the motor, how do I regulate the speed to dial it in? I can calculate the idler diameter, and build it (i think) to a high precision diameter, but how do I make slight adjustments in the speed to get it exact? How close will the motor run to the specified rpm? There has to be some tolerance on that, but how much? I hope your feeling better today.
Pfenning
Pfenning
galyons
New member
Pfenning said:
The speed of an AC asynchronous motor is driven by the line frequency. In an ideal situation, you get 60Hz at the outlet and the motor runs at the specified RPM. It is up to you to determine the motor pulley/ platter diameter ratio to generate the desired speed. In reality there are slight frequency deviations at the outlet and motors don't always run quite to spec. Additionally, bearing friction, wear , ambient temperature and lubrication will impact the delivered speed.
A good TT AC motor controller will synthesize a "perfect" 60Hz sine waveform. You can adjust the frequency of the regenerated sine wave to speed or slow the motor allowing for fine adjustment to the platter speed. Simple to describe, much harder to design, manufacture and keep costs reasonable.
It is also beneficial to reduce the voltage once the initial torque to bring the platter to speed is achieved. This will reduce vibration in the motor for quieter operation.
Cheers,
Geary
Grainger49
New member
Exactly, what Geary said. All AC tables made today that do not include a speed controller rely on the power department to keep the frequency stable. I don't think it stays off frequency for long but has periodic wavering.
The benefits I see from a dedicated speed controller are as Geary says. First, you get a stable 60 Hertz with no wandering or wavering. Second you get the voltage drop after startup. The motor torque that brings the platter to speed in a revolution or two causes hunting, dither, once the platter is at speed. Dropping the voltage drops the current and the current causes the torque. So once at speed less torque gives a steadier speed.
The benefits I see from a dedicated speed controller are as Geary says. First, you get a stable 60 Hertz with no wandering or wavering. Second you get the voltage drop after startup. The motor torque that brings the platter to speed in a revolution or two causes hunting, dither, once the platter is at speed. Dropping the voltage drops the current and the current causes the torque. So once at speed less torque gives a steadier speed.
Ok, so I understand the motor speed is set based off the 60 hertz. How do I build a speed controller like you and Geary mention? I follow you on the torque reduction idea. Can I rob the design from an existing TT (TD124 or ???)? I'm confident in my ability to build the mechanical items, but I'm pretty lost on the motor controller stuff. I need a pretty clear path to follow.
Pfenning
Pfenning
Grainger49
New member
I think that Dan and the Bottlehead crew is going to come up with a kit. I hope so.
galyons
New member
Pfenning said:
I would not considering designing and building your own controller. It is a sophisticated device that requires considerable electronics and microprocessor expertise. There was a DIY design, short lived, Mark Kelly Synchrotron AC-1 Drive Controller. Mark sold a basic board. It worked well, but, IIRC, was difficult to build and maintain. They occasionally pop up used, but I would be wary as to why!
Until BH does a controller kit, I would focus on building the TT, (no small task!), with plans to pair it with a commercially available AC controller. A used VPI PLC can be had for about $300, the much more sophisticated SDS , used for $800-900. You can source a new unit for about $380 from Phoenix Engineering , the Falcon PSU Turntable Speed Controller. There are probably a few others of which I am not aware.
I think Doc realizes that there is a DIY market for the controller, but it may well morph into the same manufacturing issues that the DAC faced. Not a small undertaking!
Cheers,
Geary
fullheadofnothing
Moderator
The TD-124 uses a shaded pole motor. It's speed control involves moving the idler on a stepped pulley that is connected by a belt to the motor. Fine speed control is done by putting drag on the pulley with a magnet with a moving shield to control the magnet's field. The motor speed is, so far as I can tell, immune to fluctuations in frequency, but sensitive to changes in voltage. DIYing this design, would be an incredible pain (and cost way more than buying a 124)
There are a lot of pages about DIYing tables. This looks pretty comprehensive:
http://www.altmann.haan.de/turntable/
Reading pages by people who have actually built these things is probably more useful than forum postings by a bunch of people who switch up cheap beer and motors. Also, I'd focus more energy on the bearing than the motor. The motor will be swappable and tuneable if you're unhappy with the results. A lousy bearing will create all kinds of problems, and be way harder to change.
There are a lot of pages about DIYing tables. This looks pretty comprehensive:
http://www.altmann.haan.de/turntable/
Reading pages by people who have actually built these things is probably more useful than forum postings by a bunch of people who switch up cheap beer and motors. Also, I'd focus more energy on the bearing than the motor. The motor will be swappable and tuneable if you're unhappy with the results. A lousy bearing will create all kinds of problems, and be way harder to change.
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