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Scratch track for camera


NKL

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I haven’t personally but I know a mixer who did for years. Sadly I can’t give you any first hand experience or tips but if you’re struggling with level you may try using an additional pre amp. I believe Mozegear makes something small that would work for this sort of application. 

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I would not recommend putting a Comtek receiver on camera as a reference track feed. They’re too susceptible to interference, especially the kind of intense RF noise that a camera is going to put out at such close proximity. Especially a camera that has a lot of accessories hooked up like a wireless transmitter, outboard monitor, follow focus, etc. Maybe if you’re using a base station to overpower that but the M216 doesn’t have a lot of transmit power to punch through in this situation. 
 

You could certainly try it and see how it goes but I suspect there would be some amount of unwanted static noise going to the camera. Maybe that’s ok for your purpose or maybe it will cause you to receive an annoying email from post. 

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Your problem may be the output cable ... I believe Comteks ship with a special 1/8"->XLR adapter cable that handles the output correctly; can't remember exactly what the wiring is, but I think it has to do with being a mono output and using a stereo plug that isn't wired correctly.

Sorry I can't be more specific, it's been a while, but it should give you a direction to troubleshoot.

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Like everyone's saying, it's not ideal.  If you want a poor man's scratch, get yourself a Lectro transmitter capable of doing IFB mode (UM400a on up essentially) and then get yourself a Sennheiser G2/G3/G4 receiver, turn off the pilot tone on the Sennheiser an voila, it will pickup the Lectro's IFB signal and sound great.  This is what I've been doing for years.

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The Documentary Sound Guy is right about the cable. It needs to be specifically wired for outputting Comtek to XLR. A regular TRS to XLR won’t work correctly.
- I could be wrong, but I have a feeling the same is true for using an R1a in the same way. 

 

Can’t remember the exact pin out, but I’m sure you can look it up online.

It has to do with the output being mono, but it’s made so that you can plug in stereo headphones and get the mono sound in both ears.

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2 hours ago, Johnny Karlsson said:

I believe that’s incorrect.

 

I just now tested a cable that I had specifically made for this purpose years ago.

 

Here is the pin out:

T - XLR 2

R - XLR 1+3

S - XLR 1+3

I am not incorrect. 

 

Your way will work too as you are not summing pins 2 and 3. The important point is that Comteks PR-216's "Left" and "right" headphone output is phase reversed from each other.

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Ok, but that looks like the regular way you would wire a balanced cable. So when you plug in to a balanced XLR on the camera, pin 2 and 3 are now out of phase -  the Comtek output is not balanced.

 

I have several cables wired that way, and they work just fine with using a UCR100 as a reference hop, but when I tried using those cables with a Comtek or R1a, there’s no signal - just as the OP is experiencing. When I switched to the wiring I posted above - it worked.

 

BTW  - Comtek sells a cable with an RF filter built in for this purpose.

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3 minutes ago, Johnny Karlsson said:

Ok, but that looks like the regular way you would wire a balanced cable. So when you plug in to a balanced XLR on the camera, pin 2 and 3 are now out of phase -  the Comtek output is not balanced.

 

I have several cables wired that way, and they work just fine with using a UCR100 as a reference hop, but when I tried using those cables with a Comtek or R1a, there’s no signal - just as the OP is experiencing. When I switched to the wiring I posted above - it worked.

 

BTW  - Comtek sells a cable with an RF filter built in for this purpose.

 

Yes, it is the way you would wire a balanced cable and it works for a PR-216.

 

I'll say it again, Comtek's PR-216's "Left" and "right" headphone output is phase reversed from each other. This has already been discussed on this forum as far back as 2014.

 

Check those cables that don't work with a multimeter. I have a feeling they have the tip and ring tied together. 

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3 minutes ago, AlexQ said:

 

Yes, it is the way you would wire a balanced cable and it works for a PR-216.

 

I'll say it again, Comtek's PR-216's "Left" and "right" headphone output is phase reversed from each other. This has already been discussed on this forum as far back as 2014.

 

Check those cables that don't work with a multimeter. I have a feeling they have the tip and ring tied together. 

I made those cables, and no they do not have 2 and 3 tied together. In what scenario would one do that?

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Ok, I just got back and did some tests here.
All cables I have on hand, some wired the way as I described above - AND the regular wiring as you describe - all work with a PR-216 plugged in to an XLR (line level) on my mixer. 
Not sure why, but over a decade ago when I had the “specific” cable made, I was told that’s how it needs to be. And weirdly, I did have situations where that particular cable worked on a camera, when the regular cables did not.

 

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On 4/28/2023 at 2:57 PM, AlexQ said:

I am not incorrect. 

 

Your way will work too as you are not summing pins 2 and 3. The important point is that Comteks PR-216's "Left" and "right" headphone output is phase reversed from each other.

Any idea why the Comtek RX has phase reversed outputs?
 

I too used UCR100’s for camera links and have many audio cables for them but had to stop using as T-Mobile started using that band in my area. I have used a couple of the UCR cables (made by Gotham, all have 3.5mm TS plugs for the Rx) with the Comtek and they seem to work. I also use those cables on Senn G3 RX and seem to work. But I need to methodically test each cable and make sure. 

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On 4/26/2023 at 8:11 PM, NKL said:

Has anyone used Comtek as a scratch track for camera? I’ve used ifb R1a before  with no issues but with Comtek I can’t seem to get any level. Any input would be appreciated. 

I do that frequently. Others commented on the 180 deg out of phase thing using TRS wired for stereo cables, but I use cables made by Gotham Sound for my UCR100 RX’s and they used TS connectors that work in UCR100, Comtek, and Senn G3 receivers. TS works, TRS may not work depending on the wiring. 

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On 5/4/2023 at 12:06 PM, stacysound said:

image.jpeg

 

Comtek OEM connector. I dont know the value of the cap.

Turns out I had two of these cables from the old days, so I butchered one of them to try and find out the values.


Holy crap it's a maze!  There are two caps and two resistors. My ability to read the value code of the resistors is shameful, so I metered them both at exactly 1 ohm. EDIT - these are inductors not resistors!
 

Cap 1 is labeled "102 A54" and the capacitance meter said .28 nF. Cap 2 is labeled "026 AHH" and metered at 1.28 nF.

 

Here's what I saw.

 

XLR Pin 1

cap 1 jumped to pin 2

jumped to pin 3

 

XLR Pin 2

cap 1 jumped to pin 1

cap 2 jumped to pin 3

1 ohm (EDIT) inductor --> 1/8" tip

 

XLR pin 3

cap 2 jumped to pin 2

jumped to pin 1

1 ohm (EDIT) inductor --> 1/8" ring and shield

 

The XLR pin one is not connected to a wire, only jumper to its neighbors.

 

The 1/8" connector is a TRS style, but the sleeve and the ring are connected. The white went to pin 2, and the red and shielding went to pin 3.
 

So, everything is connected together and I am thoroughly confused! I would love it if some smarty-pants could explain what the electrons are doing.
 

5362F909-892E-4575-A11E-DD4B4F75DEED.jpeg

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https://www.instructables.com/Inductor-Color-Code-Guide/
 

I read 7.5 uH 10% but I'm not that familiar with military markings. Anybody that is, chime in.

At 216 MHz that inductor would have a reactance of 10k Ohms or effectively an open circuit for RF.  The 1 Ohm resistance you measured would be at audio frequencies.

 

Those values pass the smell test. The inductor value is not critical. Any value from 2 to 8 uH will work. The 7.5 uH is little high in my judgement but that value would also work down at 72 MHz which may explain the higher value.

Best Regards,

Larry Fisher

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