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Wet to Dry IFB adaptor wiring


Tim Paul

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I've got a shoot coming up where I need to hook my LMa up to the truck for talent IFB. I'm betting the truck can send me a dry line. However, they have not yet found a truck, so I can't talk to them to confirm. I'm hoping someone can help me with a schematic to make a wet/dry XLR adapter cable. Thanks!

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...what? Are you trying to use the LMa to transmit TO a truck radio? Or trying to use a truck radio mic with the LMa as a transmitter?

 

Truck = TV production truck or audio production truck.

Dry line = just audio  no dc bias current.

Wet line = an output with both audio and dc on it.

 

A standard analog phone line is a wet line, for example, as are intercom lines.

 

It's been some time and somebody else might have a better answer, but I think a pair of 1 uF 200v 10 uF 50v. caps in line will block phantom on a line. If the caps are polarized, the plus side should point to the truck or source of phantom power. It's been long enough that I can't remember if there's a better way if you're worried about a typical telco wet pair.

Best regards,

Jim

 

Edited to reflect the values I found in my notes.

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Truck = TV production truck or audio production truck.

Dry line = just audio no dc bias current.

Wet line = an output with both audio and dc on it.

Intercom lines are "wet," for example.

Best regards,

Jim

Interesting. I've never heard them referred to like that. Haven't done that much truck work, though. Thanks for the lesson!

So in that case, a 'wet to dry' adaptor would be something like a capacitor-based DC block, and a 'dry to wet' would be akin to a DC injector (Bias-T style) or something...?

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Interesting. I've never heard them referred to like that. Haven't done that much truck work, though. Thanks for the lesson!

So in that case, a 'wet to dry' adaptor would be something like a capacitor-based DC block, and a 'dry to wet' would be akin to a DC injector (Bias-T style) or something...?

It's been a while since I used that part of my brain, Justin, and I remembered some things, so I edited my post. Something like the Berringer Ultra-DI 100 would also work as would any line level capable isolation transformer, like the VMS-4 that Vark Audio makes.

Best regards,

Jim

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The majority of Sat trucks I've worked with tell me they can't give me a dry IFB feed.   I use either a Sescom IL-19 http://www.markertek.com/Audio-Equipment/Audio-Processing/Audio-Hum-Noise-Eliminators/Sescom/IL-19.xhtml or my whirlwind 3 way splitter and make sure you connect your LMa Tx to the XLR output that has the isolation transformer on it.  http://www.markertek.com/Audio-Equipment/Audio-Interface/Mic-Splitters/Whirlwind/SP1X3.xhtml

 

Andy

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The majority of Sat trucks I've worked with tell me they can't give me a dry IFB feed. I use either a Sescom IL-19 http://www.markertek.com/Audio-Equipment/Audio-Processing/Audio-Hum-Noise-Eliminators/Sescom/IL-19.xhtml or my whirlwind 3 way splitter and make sure you connect your LMa Tx to the XLR output that has the isolation transformer on it. http://www.markertek.com/Audio-Equipment/Audio-Interface/Mic-Splitters/Whirlwind/SP1X3.xhtml

Andy

I had a sat truck fry the transformer of a whirlwind imp 1X3 splitter by sending me a wet line - the truck operator thought that it was dry.
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Andy, you just answered my question... I have a couple IL-19's, I was going to ask Jim if they would do the job. Thanks for answering my question before I even asked!

I may build a barrel with caps just to keep in my IFB kit, but it's nice to know I don't have to build it right away.

Thanks again guys! You have all been a huge help!

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It has been decades since I did this process, and have completely forgotten how we achieved it back in the early 90s. 

I thought we used drypair adapters somewhere in the chain...

 

I think RTS PLs can pack as much as 50v down the lines....

 

Would the Shure A15BT work in this capacity?

 

http://www.fullcompass.com/product/435414.html?utm_source=googleps&utm_medium=shopping&utm_campaign=googleps&gclid=CP3T-onDircCFdJ9OgodIEoAEA

 

The link claims it can also serve as an isolation transformer - might be a less expensive way to achieve the result.

 

Based on previous good results of course -- Does anyone have a thumbs up for this inline solution?

 

MF

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I have always used a Whirlwind Splitter isolated output for Wireless IFB.  Also great for splitting the signal to different devices.  I run the IFB into my 664 to feed my IFB transmitter on a Aux and also create a custom headphone preset so I have it in one ear as well, therefore I dont need to take up an IFB box.

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I tested out my IL-19's with 48v phantom power, sure enough according to the meter no power passes thru. I made a short XLR jumper with 10uf 50v non-polarized electrolytic caps in line with pins 2 and 3. According to the meter the cable is still passing about 42v. What am I missing to make this cable work?

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According to the meter the cable is still passing about 42v. What am I missing to make this cable work?

It's a combination of the very high meter input impedance and a miniscule capacitor leakage curent. As soon as you load either or both legs to pin 1 it will act as you expect. As a by the by, you don't need non polarised caps. Polarised with the + towards the phantom is fine.

 

Rob

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