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Old 31st January 2004, 01:26 PM   #1
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Default XLR cables

I've searched the forum and found a lot of topics on balanced - unbalanced XLR leads and vice versa. However, people seem to have many different solutions to the problem.

What is the best solution to convert from balanced to unbalanced, and vice versa? I'm looking for a solution that wont require the opening of modification of any equipment other than the leads. I don't mind using transformers as long as they are easy to get hold of in the UK and will fit inside the XLR body. Any ideas for the following would be much appreciated:
> XLR to XLR with transformer to prevent ground loops
> Balanced to unbalanced connections
> Unbalanced to balanced connections

I will be very grateful for any and all advice

Matthew
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Old 31st January 2004, 05:32 PM   #2
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You've got no chance fitting a transformer inside an XLR!

For balanced to unbalanced, just don't bother connecting the 'cold' pin, i.e. you can use 2-core screened cable.

For unbalanced to balanced, either use 2-core cable as above and short the cold pin at the balanced end. However this loses all the benefits of the balanced connection.

If you want to have the benefits of balanced connections you need to use an unbal-bal converter at the unbal end. You can build one of these to fit in a small box. Or use a transformer, but I don't think they are that easy/cheap to get hold of new nowadays.

Check out the ESP site for just the project you need.

I have made a PCB myself to do what you want and you are welcome to have the layout (I may even have a spare board lying around), but I only have a hand-drawn component layout diagram, so you would be fending for yourself a bit.
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Old 31st January 2004, 05:39 PM   #3
dhaen is offline dhaen  Europe
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Default I love transformers but...

There has been endless discussion on balanced and unbalanced conversion. It's all on the forum with a bit of effort in searching.

Search terms that might be useful:
unbalanced
balanced
transformer
DRV134
SSM2142
SSM2141
XLR
Twisted

WRT transformer size: You will not find a transformer that will fit inside an XLR connector that can handle both high levels, and LF. Such adaptors are available commercially, but tend to be used for low level signals, or where frequency response is unimportant.

Remember also that unbalanced and balanced standard have different levels (balanced is much higher), so transformers are limited.
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Old 31st January 2004, 07:18 PM   #4
Vaihde is offline Vaihde  Finland
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Lundal and Neutrik have some thing like that

http://www.lundahl.se/catframe.html
http://www.neutrik.com/
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Old 2nd February 2004, 08:35 AM   #5
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Thanks for the quick replies. I think I'll end up using balanced line driver IC's. However, what effect will this have on phantom power?

Thanks again

Matthew
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Old 2nd February 2004, 08:39 AM   #6
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Sorry, just to clarify the above, I understand that the circuitry can be fed from phantom power. However, will I still have phantom power on the output?

Matthew
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Old 2nd February 2004, 11:32 AM   #7
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Phantom power is usually done 'from' inputs and will not automatically be there if you make your own i/p or o/p circuitry. If you know you are connecting to something with phantom power, make sure the o/p of the source has DC-blocking capacitors.

The ESP site that I linked to has a full explanation of phantom power.
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Old 2nd February 2004, 01:47 PM   #8
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The best way to convert between balanced/unbalanced is undoubtedly to use a transformer or some active circuitry. You could try http://www.canford.co.uk/ for posh-but-expensive stuff.

Otherwise, what exactly are you converting to and from? If a piece of kit has a balanced line output and you want to feed it into an unbalanced line input, run a balanced line all the way to the input, then connect cold to signal ground at the input.

If you're talking balanced microphone to unbalanced mic input, the same trick will work, unless (a) the impedances are different (balanced mics are almost always low-Z, unbalanced inputs may be high-Z), or (b) the mic is phantom-powered. In case (a) you'll need a transformer, in case (b) you'll need a power supply of some form.

For unbalanced output to balanced input, generally connect 'hot' to the unbalanced signal, and 'cold' and balanced ground to unbalanced ground. This is best done at the unbalanced end. If you have problems with ground loops, you can insert a 100 ohm resistor between balanced and unbalanced grounds (keeping cold wired to unbalanced ground).

Hope this helps.

Cheers
IH
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Old 2nd February 2004, 02:25 PM   #9
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Direct Injection (DI) boxes are a very good way of converting, and I believe the Behringer units can go both ways. These are usually able to be phantom powered, however the phantom power will not be relayed to the other side - which would not be possible with ground isolation anyway.

Cheers
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Old 2nd February 2004, 02:54 PM   #10
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OK, I understand what you're saying now. If I've read the schematics from the ESP site properly, is it just a case of putting power onto the line through 1.5k resistors?

Matthew
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