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Balanced to unbalanced converter


Stuart91

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Someone has asked me to help on a problem they have with some wired IEM packs. They are using Fishman headphone amps, but they only have an unbalanced input, which is presented on a TRS jack in stereo.

 

So far, they have been driving that from a mixing desk (down ~40m of multicore) and using an adaptor to get into the packs. At the moment their big problem is that they only get one side of the headphones driven, which can be easily sorted with a change to the wiring. However the biggest problem is that the input unbalances the line. If they were coming out of a desk on stage I wouldn't be too worried, but when it's driven from FOH I can see potential problems.

 

They have virtually no budget available, so buying new/better packs is not going to be an option. So what I'm looking for is a cheap/easy way to take the balanced line, and derive an unbalanced output from it. Some isolation would be nice but I'm not sure they will swing for proper transformer isolated stuff. If there's a simple circuit that we could build for them that might be the easiest option. There are six packs in total, which will all need driven with their own mix.

 

I can find this from ART as an off-the-shelf option which they might stretch to if building something is going to be too much hassle. Does anyone have any experience with it?

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I have one which I used to use when DJing at clubs with my laptop; removing the noisy PSU hum cleanly and without any noticeable degradation to the audio signal.

I still use it now and again for playback inputs when I don't need a DI to pad the signal level down.

 

edit: Oh yeah, and I was using it to go unbalanced to balanced without any issues. That was on a short run, so maybe best used at stage end rather than FOH?..

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Similar idea to others, something like this mic matching transformer is what I've used in the past for a similar purpose (balanced desk AUX output to distant powered foldback speaker with 1/4" unbalanced line input)

 

http://www.gear4musi...Transformer/NRP

 

If you're that desperate for cheap I've got one in bits and you can have the audio transformer from it if you want...

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http://www.maplin.co.uk/p/ground-loop-isolator-vw43w

 

Two isolating transformers in a can

 

rewire it for one winding having XLR on 2 & 3 NO ground, output as unbalanced with a phono to jack adaptor.

 

Otherwise open the can and use one transformer.

 

Big Clive dot com (of this parish) did a youtube vid of opening one of these.

 

added;

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http://www.maplin.co.uk/p/ground-loop-isolator-vw43w

 

Two isolating transformers in a can

 

rewire it for one winding having XLR on 2 & 3 NO ground, output as unbalanced with a phono to jack adaptor.

 

Otherwise open the can and use one transformer.

 

Big Clive dot com (of this parish) did a youtube vid of opening one of these.

 

added;

 

I've had one of these in the past and they do their job well. They are a bit "hifi" but they work. As also said earlier in the post, as with everything in life, only go to Maplin if your desperate! Same thing is 25% of the cost else where.

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Have you tried using the pair and ignoring the ground, taking one to hot and other cold - if the driving device is a differential type, then with line level, there's no need for earth continuity. Depending on the headphone end of things, it will either work perfectly, or not. Worth a go, and makes the problem possible to solve without spending anything.
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Thanks, Paul - that sounds like an interesting possibility. Apparently they are just driving this from the aux outputs of an analogue desk, I think it's an A&H GL series or something similar.

Um, you could be running into trouble there. It'll only work if one or both ends have no earth reference - the desk end definitely will have, but if your IEM amp is battery powered or powered from an independent non-earthed power supply then it would be OK. If there's a common power supply to several IEM amps it won't work.

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