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Old 21st May 2006, 10:40 AM   #1
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Default Video Head TT bearing

I am planning to build a turntable to go with the rest of my DIY system, as this is my first turntable project which I will treat as a learning process I am looking to make it as cheap as possible.

My plan is to make the platter from layers of MDF/thin rubber and use a floppy drive motor, with a home grown unipivot arm. The bearing is the one aspect I have not nutted out properly.

But what a bout a video head, I have several.

Now I know that this type of bearing is not the accepted norm, but I have tried a little test that looks promising.

I got a bearing with head attached, mounted a bare alloy platter to it with blu-tack and sat the bearing/assembly in a coffee jar for support. Very interesting the bearing spins for ever with no effort, far far better than the best turntable I have (which is a good quality high quality 70s Pioneer belt drive). There is the faintest amount of bearing noise with the raw thin platter, but its better than all other tables I have except the Pioneer, but it has a damped platter and it is not that much better. The main source of noise on the Pioneer is motor noise, hardly surprising the motor looks like it could drive a mini lathe (well not quite but you get the picture)

Now I should point out a couple of things, this is actually a dud bearing/head, as I dropped it and it has got grit in the bearing, so a near new one would be vastly better. I imagine most of the noise is due to the grit and the dry state of the bearings.

So good is the bearing friction wise that I can start the platter by blowing across it!

Theres no play that I can feel.

The only difficulty I can see is getting it all centred, but I think I can do that.

So I wonder why wouldn't it work with a platter of moderate weight, has anyone done this and if so how did it go.
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Old 21st May 2006, 06:47 PM   #2
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Default Re: Video Head TT bearing

Quote:
Originally posted by Zero One


But what a bout a video head, I have several.

Now I know that this type of bearing is not the accepted norm, but I have tried a little test that looks promising.

So good is the bearing friction wise that I can start the platter by blowing across it!

Theres no play that I can feel.

The only difficulty I can see is getting it all centred, but I think I can do that.

So I wonder why wouldn't it work with a platter of moderate weight, has anyone done this and if so how did it go.

I haven't tried a video head bearing but have been using a bearing out of a 1970's IBM server harddrive for a a few years. Technically both bearings were not meant to be loaded in such a manner, but in my case I believe the bearing was over designed and It has shown no signs of wear. I took the bearing and my platter to a machine shop and they located the mounting holes and machined the platter to match. Actually quite cheaply.

As you noted the friction and noise is unbelievably low.
I'd say give it a try. Most people listening to my turntable can't believe records can be that quiet.

Mike.
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Old 21st May 2006, 07:20 PM   #3
AuroraB is offline AuroraB  Norway
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This might do OK with a low mass platter....but could also be a good candidate for the horisontal movement of a tonearm...
-- think I saw this somewhere on the net some years ago..
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Old 22nd May 2006, 01:35 PM   #4
pixpop is offline pixpop  United States
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I wouldn't worry about the axial loading. It might mean the bearing wears out sooner than expected.. nut so what. They cost nothing.

Although you can't hear noise in your experiment, don't be surprised if your cartridge can hear it when playing a record. I think there's a good reason why ball bearings are almost universally absent from turntable spindles.

I actually tried a similar experiment, but I was testing the video head motor as a possible direct drive turntable motor. It couldn't run slowly enough with the electronics from the VCR, but I think it would with a specially built driver. I think the VCR motor would also make a good belt drive motor.
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Old 22nd May 2006, 01:56 PM   #5
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Hi Pixpop

I tried another bearing today that was in good condition with a platter design I am lookng at, there is a post about this .

The whole set-up is amazingly fluid and utterly silent, more so than than the Pioneer table I mentioned.

I think the video head motor could work too, I also have looked at video capstan motors, and a couple of very good cassette drive motors I have. Id say the video head one at a fairly low speed would be very close to silent, especially if in a seperate pod away from the platter. I wnder how you actually control the things, I have another 2 of them. Overall I think video head motors should be of high quality. Any idea of what speed they normally run at?

The idea with this project is keep it cheap but make it good.
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Old 22nd May 2006, 02:32 PM   #6
pixpop is offline pixpop  United States
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I think they run at 3000 RPM in 50 Hz countries. I think they make one revolution per video frame. I've successfully salvaged the drive electronics from a couple of VCRs. The older ones are very easy to work on. The ones I did are both DC servo systems. You feed in a DC voltage to control the speed. It's not the motor that has a problem running slowly. It's the drive electronics, which are really optimized for 3000 RPM. However, I do think they would run slowly enough to be a belt drive motor. They do seem to run very quietly.

The capstan motors are frequency locked. So to control the speed, you need to feed in a clock signal of the right frequency. They seem to have more torque than the head motors, and might make better belt drive motors.
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Old 22nd May 2006, 03:29 PM   #7
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Quote:
Originally posted by pixpop
I think they run at 3000 RPM in 50 Hz countries. I think they make one revolution per video frame.
Depends on the number of video heads in the drum, usually 2 or 4. But there are drums with 5 heads (Hitachi if I remember well). If you have a chance look for an old U-Matic semi-professional machine, although these become rare and collector items. These machines have much larger drums and sturdier bearings than the usual VHS machines.

Cheers
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