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Georg Jensen Model 504 motor for Arri 16S


Duncan Brown
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Here are some pictures of a motor I picked up a while back and am just now looking into.  It's a Model 504 motor by "Georg Jensen Denmark" that's spec'd to 24fps.  I was going to ask if anyone knew anything about it because I could never find anything via google (except that a guy named Georg Jensen makes lots of sterling silver items!), but since I last looked, Pacific Rim Camera has put up a very helpful brochure:

https://www.pacificrimcamera.com/rl/01130/01130.pdf

That answers almost all my questions - it's crystal sync, it can run on either 8v or 12V, nice motor!  It seems to work, I'll have to do some tests on 8V and 12V and see if it's really synced at 24fps in both cases.  I do wonder what the little jack is on the camera side of it - Pilotone signal maybe?  I'll have to look at that with a scope.

Duncan

 

 

georg_jensen_model_504_01.jpg

georg_jensen_model_504_02.jpg

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11 minutes ago, Steve Switaj said:

I'm not familiar with the Arri S/B's. Where's the power connector? Is it a blind mate to that little metal pin at 7 o'clock on the motor face?

Yes.

Neutral is the motor case itself. Hence the insulating cap.

I don't know what the jack is for either. There doesn't seem to be room on the back of the camera for anything to plug into it.

Edited by Mark Dunn
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59 minutes ago, Mark Dunn said:

Yes.

Neutral is the motor case itself. Hence the insulating cap.

I don't know what the jack is for either. There doesn't seem to be room on the back of the camera for anything to plug into it.

No, it definitely doesn't plug into anything on the camera.  It's situated such that a cable could plug into it while the motor is mounted to the camera.  (I'll have to add a picture showing this.)  I really can't think of anything besides a Pilotone signal that you'd want from inside a motor.

As to the other question, yes, inside an Arri 16S there is a switch leaf with a contact on it, that the similar button contact on any of the motors for it hits against as the motor is slid in, with enough pressure to make solid electrical contact.  There is a nub on all the motors that mates with a little notch in the motor opening, to make sure the motor is locked in the correct orientation to make the contacts line up.  Clever, elegant design, really.

Duncan

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I'm still trying to figure out what kind of jack it is (I moved a year ago and can't find my box of various plugs...yet...) so I can hook up a scope.

I believe the actual Pilotone signal would only need two wires, though a lot of camera "Pilotone" connections had more, for also passing through audio from  some near-camera source, etc.  It's just a sine wave at some known frequency.

I'm about as far from a Pilotone expert as one can be, having never actually used it, but as I understand it unless you have a crystal-controlled motor on the tape deck too (and maybe not even then, if you're dealing with wow and flutter), you're still going to need a signal from the camera that's a known frequency to match your recorded audio up against.  So even with a crystal motor like this, there could still be situations where you'd use an output signal from it to match up audio.

Duncan

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27 minutes ago, Mark Dunn said:

I don't know the dimensions, does 3.5mm seem right?

It definitely looks bigger than 3.5mm - by eye I'd say it's "that next bigger size up that everything used to use, like microphones and things on stereo gear" but not as big a a phone plug.

I tried to use some gear at work to peer down into it, just to make sure it IS a jack, and not, say, a collar leading to an adjusting screw, but its location and depth make it very hard to see into its interior.  I'm hoping if I get a plug to "click" into it then I'll know it's really a jack.

Duncan

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I could only find a stereo version of that plug, which often but not always works in a mono jack.  Clicked in OK, and I got a signal on the center pin with the motor running.  But the signal makes no sense.  It's a triangle wave, noisy, and not perfectly stable...and it's a little over 7KHz (I was expecting 1KHz).  So yeah, I'd love to know what that jack is supposed to be for.  I suppose it's always possible that someone stopped using this motor because the Pilotone signal was no longer good, or that nobody ever noticed it was bad because nobody used it with Pilotone...but it's also possible my theory about what it was is all wet,

Duncan

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17 hours ago, Duncan Brown said:

I could only find a stereo version of that plug, which often but not always works in a mono jack.  Clicked in OK, and I got a signal on the center pin with the motor running.  But the signal makes no sense.  It's a triangle wave, noisy, and not perfectly stable...and it's a little over 7KHz (I was expecting 1KHz).  So yeah, I'd love to know what that jack is supposed to be for.  I suppose it's always possible that someone stopped using this motor because the Pilotone signal was no longer good, or that nobody ever noticed it was bad because nobody used it with Pilotone...but it's also possible my theory about what it was is all wet,

Duncan

do you have any screenshots of the waveform from oscilloscope, it can be possible to figure out from it what is going on

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44 minutes ago, aapo lettinen said:

do you have any screenshots of the waveform from oscilloscope, it can be possible to figure out from it what is going on

some motors may have a reference voltage generator with carbon brushes and that causes tons of noise and waveform breakage with uneven frequency stepping

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13 hours ago, aapo lettinen said:

do you have any screenshots of the waveform from oscilloscope, it can be possible to figure out from it what is going on

See attached.  Sometimes it's a perfectly clean signal, sometimes it's got more noise than signal, this is kind of in between at the moment I captured it.  I'm wondering if any of this is artifacting from the low-budget digital scope.  I might have to drag out the old Tektronix analog scope and see if I see anything different.

Duncan

image.thumb.jpeg.0dc9dda28c165ad2ff7bf8594c2c636f.jpeg

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37 minutes ago, Duncan Brown said:

See attached.  Sometimes it's a perfectly clean signal, sometimes it's got more noise than signal, this is kind of in between at the moment I captured it.  I'm wondering if any of this is artifacting from the low-budget digital scope.  I might have to drag out the old Tektronix analog scope and see if I see anything different.

Duncan

image.thumb.jpeg.0dc9dda28c165ad2ff7bf8594c2c636f.jpeg

can you add screenshots of the noisiest and cleanest signals you can get from it and some data about how much the frequency fluctuates back and forth or if it stays perfectly stable. And does it just start and stop when running the motor or does it speed up and slow down?


The sawtooth wave looks like artificial, made probably with a rc low pass filter tuned just right. The noise present is probably noise from within the motor itself caused either by the crystal electronics or the motor drive itself.

sawtooth wave is often used for generating motor control signals but I don't see why a pilotone signal would need to be a sawtooth wave and why the frequency is so odd. Probably it is meant for other purposes, maybe some external accessory originally included with the motor

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23 minutes ago, aapo lettinen said:

can you add screenshots of the noisiest and cleanest signals you can get from it and some data about how much the frequency fluctuates back and forth or if it stays perfectly stable. And does it just start and stop when running the motor or does it speed up and slow down?


The sawtooth wave looks like artificial, made probably with a rc low pass filter tuned just right. The noise present is probably noise from within the motor itself caused either by the crystal electronics or the motor drive itself.

sawtooth wave is often used for generating motor control signals but I don't see why a pilotone signal would need to be a sawtooth wave and why the frequency is so odd. Probably it is meant for other purposes, maybe some external accessory originally included with the motor

OK the analog scope does a better job of showing what's really going on - these are successively shorter timebases so you can see there's actually a higher level pattern to the noise that comes and goes.  The underlying frequency of the base wave doesn't really change from about 7KHz but the cheap digital scope has a really hard time deciding what it is because of all the noise.

I'm actually starting to wonder if this is an INPUT that we're just seeing internal motor noise on because nothing is plugged into it!

Duncan

 

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georg_jensen_model_504_06.jpg

georg_jensen_model_504_07.jpg

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Oh, and according to my iPhone tachometer app it's running dead-on at 24fps with an 8.4-ish VDC power source (7 1.2V NiMh batteries).  I've not had a 12V motor for my 16S before so I'll have to rig up a cord for that before I can test it with 12V but I'm guessing that will be a perfect 24fps too.

Duncan

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6 hours ago, Duncan Brown said:

Oh, and according to my iPhone tachometer app it's running dead-on at 24fps with an 8.4-ish VDC power source (7 1.2V NiMh batteries).  I've not had a 12V motor for my 16S before so I'll have to rig up a cord for that before I can test it with 12V but I'm guessing that will be a perfect 24fps too.

Duncan

Which app are you using?

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Yeah, I've found that playing with the ambient light vs the app's light can help get a better image sometimes.  It does have trouble focusing close-up, and close-up is often how you're using it.  But hey, the price is right compared to a professional strobe light tach tool!

Duncan

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  • 3 weeks later...
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Finally got a chance to kludge together a 12V cable for this.  (I don't want to hack up an original 16S cable, so I made an XLR-to-far-end-of-16S-cable adapter of sorts and gaffer-taped it all together...)

To nobody's surprise, it runs dead on at 24fps when on 12V too.

I was totally OK running this camera at its original voltage but I have a couple of generic camera belts I need to recell and if I could just make them both 12V and run all my cameras from them I could see the appeal of going 12V.  (In addition to this crystal sync motor, I have the later Arri A16HME variable speed motor, which is supposedly fine to run at 12V or 8V).

Duncan

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