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Something every SD788 and Lectro owner should know...


Sound Art Film

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Hi all,

 

I have been having issues with my Lectro units when working with my 788.  The problem arises when my lectros are connected via XLR inputs on the 788.  The difference in available frequencies is dramatic when the 788 is turned on and my units are connected via XLR to the 788. 

 

When the 788 is on and I scan with my lectros, and without being connected to the 788, I get minimal RF spray, even when the units are right next to the input section. 

 

After doing some investigation I came across this page on SD's website: http://www.sounddevices.com/notes/recorders/788/788t-w-wireless-in-38-40/

 

I inspected my XLR's from 411a to 788 and discovered that the ground pin had not been connected to the housing of the connector.  Also, I inspected my Y cable for my SRB5p and noticed that the ground pins had not been connected to the housing either.  After doing the modification to the XLR, my available frequencies improved quite a bit for the 411.  However, even after doing the mod for the Y cable for the Srb5p, I got no better results.  my theory is that the shield in the thin cables is not sufficient to help block the RF interference no matter what. 

 

At this point, I remembered reading that the RF leakage was much less using the TA3 inputs on the 788.  After soldering two new cables to go from the TA3s from the SRB to the input of the 788, I discovered that I had much more available frequencies on the Srb5p. 

 

Case in point:  It appears from my testing that if you are going to use Lectrosonics receivers with the 788 and route through the XLR input, make sure your XLR, on the male end, has the ground pin attached to the housing of the connector.  If possible, it appears the TA3s have a lot less RF problems than the XLRs and are a good choice to choose for routing Lectro units into the 788. 

 

My setup

 

788: All channels activated and routed to tracks.  Powered by Sony NP-970 L mount battery. 

 

Lectrosonics 411a and Srb59: 411: Block 22, Srb5p Block 20.  411 powered by two 9V lithium batteries.  Srb5p powered by L mount battery. 

 

XLR: 12"

 

Y cable: Made by Pro-Sound as Y cable for ta5f, terminated with two XLR male.  12"

 

Pictures and examples below:

 

Units scanned with 788 off and not connected

 

No%20SD,%20Not%20connected.JPG

 

 

Units scanned with 788 on, not connected.

 

SD%20on,Not%20connected%20close.JPG

 

Units scanned, connected via XLR inputs on 788, 788 on. 

 

SD%20on,Connected%20XLR,TA5f,No%20mod.JP
 

Units scanned, connected via XLR with ground pin connected to connector housing.

(notice difference on 411, but not on Srb5p)

 

SD%20on,Connected%20XLR,TA5f,%20With%20M

 

Units scanned, modded XLR connected to 788 and 411, modded Y cable connected to 788, but not connected to Srb5p, 788 on. 

 

SD%20on,Connected%20XLR,No%20TA5f,with%2

 

Srb5p scanned, Y cable attached to 788 via XLR, no 411, 788 on.

 

Just%20ta5f,%20with%20mod,%20plugged%20i

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Thanks for the pictures and the good experiments. I will just mention something that I am sure everyone understands and that is this would affect any brand or type of receiver that operates in the same UHF band. So these real world tests would apply to any receiver setup.

Again, thanks for the excellent input.

Best Regards,
Larry Fisher
Lectrosonics

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Hey Larry,

Thanks for the clarification. I assumed that was the case,but did not want to erroneously include other brands that I did not test first. I'm glad that you appreciated the experiment!

Yasou Vasileios,

No transmitters used, just receivers.

Thanks to everyone for chimming In so far!

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Hey Larry,

Thanks for the clarification. I assumed that was the case,but did not want to erroneously include other brands that I did not test first. I'm glad that you appreciated the experiment!

Yasou Vasileios,

No transmitters used, just receivers.

Thanks to everyone for chimming In so far!

 

Oh sorry. My fault. :)

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Thanks for doing these tests! I contacted Sound Devices & was told this would void my warranty

so will wait until it expires before trying it out. Just a heads up for anyone thinking about jumping straight

into it like I did.

What warranty breaking  modification? All this was done inside the cables. Or I'm missing something (which is not unusual).

Thanks,

LEF

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  • 2 weeks later...

Hi, I'm new here on this forum. I have a SD788 and will probably soon buy my first Lectrosonics system. SRb & SMV

Are there more known RF problems with SD788 and Lectro? These tests were at block 20 & 22. I was thinking about buying a system in block 24. Should I be worried or what?

I've googled my ass off, but can't find any answer. I have seen a lot of people using 788/Lectros but haven't heard that there could be a problem.

Regards

John

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The title of this thread is a bit misleading. The problem isn't just Lectros; it is a 788 problem and would be with any receiver of any type. RF on a carrier frequency will reduce the sensitivity (range)of any receiver and reduce the sensitivity exactly the same amount. Lectros just happened to be the system the poster was using with the 788

Larry Fisher

Lectrosonics

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