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Author Topic: Unbalanced to balanced (yes, this again)  (Read 5712 times)

Gerry Seymour

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Unbalanced to balanced (yes, this again)
« on: May 12, 2013, 09:22:10 am »

I'm looking for a solution for connecting unbalanced line-level signals to a balanced XLR input in conference rooms. Here's the situation:

I travel and deliver training seminars, mostly in hotel conference rooms. I bring my wireless mic with me and my own speaker (GoSpeak, which has an integrated mixer), which is also used to amplify the sounds from some demo's on my PC and a bit of music during breaks. This works fine, but isn't as good as using the installed system in some situations (especially larger groups).

My intention is to carry a small mixer with me just for connecting to the installed systems (though the situation is the same if I use the line-out from my GoSpeak). All of the small mixers I've looked at, including my Alesis Multimix 4, have outputs designed for connecting to nearby speakers (phone, mini, or RCA) rather than XLR outputs. All of these are unbalanced, and either dual mono (always the case with RCA, obviously) or a single TRS stereo output. In all cases, I'm looking at stereo (either dual mono or single stereo) out to a mono in (the XLR).

So, here's my question: how much care do I need to take in getting these signals from unbalanced stereo RCA/phone/mini to balanced mono XLR? I know just using a Y cable to combine the two channels into a single mono channel isn't optimal, but does it really lose anything important in a situation like this? And am I okay with a simple transformer/adapter to go from unbalanced to balanced?

I'd prefer to do this all in one cable/adapter (so much kit to carry on these trips, every ounce and cubic inch counts). Of course, I can't ask for specific recommendations for that until I figure out which tiny mixer I'll be using.
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Gerry Seymour

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David Sturzenbecher

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Re: Unbalanced to balanced (yes, this again)
« Reply #1 on: May 12, 2013, 09:41:18 am »

When you use a Y cable, the output amplifier of one channel not only drivers the input stage of whatever is receiving the signal, but also the output stage of the second channel. In general, an output likes to drive impedances 10 times that of itself. In this case its driving an impedance almost equal to itself. This can cause colorations of the sound at best. 

Here are two good choices that sum to mono, and balance an unbalanced signal

http://www.rapcohorizon.com/p-377-ltiblox.aspx

http://whirlwindusa.com/catalog/black-boxes-effects-and-dis/transformers-isolation-devices/isopod
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Gerry Seymour

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Re: Unbalanced to balanced (yes, this again)
« Reply #2 on: May 12, 2013, 10:37:37 pm »

Here are two good choices that sum to mono, and balance an unbalanced signal

http://www.rapcohorizon.com/p-377-ltiblox.aspx

http://whirlwindusa.com/catalog/black-boxes-effects-and-dis/transformers-isolation-devices/isopod

Not only do those do what I need (sum to mono, convert to balanced), but they do it with gear that will fit in my zipper pouch of adapters. Nicely done, David!
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Gerry Seymour

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anything that moves will eventually die

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Brad Weber

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Re: Unbalanced to balanced (yes, this again)
« Reply #3 on: May 13, 2013, 06:44:03 am »

Not only do those do what I need (sum to mono, convert to balanced), but they do it with gear that will fit in my zipper pouch of adapters. Nicely done, David!
Just keep in mind that apparently one of those devices provides a line level output and the other a microphone level output.  If you need to go into microphone inputs and want something more flexible you may want to look at something like http://whirlwindusa.com/catalog/black-boxes-effects-and-dis/direct-boxes/pcdi, http://www.procosound.com/iface or http://www.radialeng.com/r2011/proav.php.  All of those provide or can be set to provide a mono mic level balanced output.
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Jerome Malsack

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Re: Unbalanced to balanced (yes, this again)
« Reply #4 on: May 13, 2013, 10:58:59 am »

You might also need to get a Horizon Ground lift adapter with those to prevent any hum.   
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David Kaiser

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Re: Unbalanced to balanced (yes, this again)
« Reply #5 on: May 21, 2013, 09:59:57 pm »

The smallest mixer I know of with XLR outputs is the Mackie 802VLZ3. Or go with the Radial PROAV1.
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Jordan Wolf

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Re: Unbalanced to balanced (yes, this again)
« Reply #6 on: May 22, 2013, 11:44:11 pm »

Gerry,

I'd recommend a smaller mixer like the Soundcraft EPM6.  It has a usable EQ for our wireless microphone, and enough channels to add things in later if necessary.  It also has XLR outputs (live level) so you can drive long lines without worrying about signal degradation.

I'd say buy a couple of -30dB pads to stick inline if you MUST use mic-level inputs.  I always give people the option of Mic or Line (if I get the "deer in the headlights" glare, I know I need to ask more questions).

If you're ever in Philadelphia, I'm at the Hyatt Regency at Penn's Landing. :-)
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Gerry Seymour

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Re: Unbalanced to balanced (yes, this again)
« Reply #7 on: July 21, 2013, 11:08:37 am »

Just noticed there were more replies after my last post on this thread, so I thought I'd reply to them, in no particular order.

Jordan: A good solution (EPM6), but a bit larger than my current mixer (Multimix 4). Since all of my gear has to be carry-on (one roll-aboard, one briefcase - have to carry it all on due to scheduling on some trips), I'm trying to keep things as small as possible. I've actually been looking at smaller options, rather than expanding capabilities. Long runs are never an issue (have never had a run longer than about 25-40'). I'll certainly be in the Philadelphia area at some point - I'll look you up.

Brad: those are effective options, but I'm back to the space limits. My bags tend to be fully stuffed (all my gear, my instructional materials, business clothing for a full week, etc.), so I hesitate to add anything larger than the LTIBLOX or a cable. Your recommendations are going on my list of car-travel gear, though.

Jerome: I do carry a ground lift adapter - have needed it more than once.

Thanks to all for the suggestions. Will be building a car-portable kit in the future, with more flexibility (and power). Some of these suggestions will go in that kit.
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Gerry Seymour

Professional Trainer and Speaker
(with lighting/audio experience)


anything that moves will eventually die

anything that doesn't move is probably already dead - James Feenstra

Jordan Wolf

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Re: Unbalanced to balanced (yes, this again)
« Reply #8 on: July 22, 2013, 11:55:51 am »

Gerry,

Have you considered an audio interface that you can use with or without a laptop?  You could do direct playback from your laptop (I'm almost certain you'd carry one).

MOTU makes a few that are standalone capable.
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Jordan Wolf
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Ned Ward

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Re: Unbalanced to balanced (yes, this again)
« Reply #9 on: July 29, 2013, 04:18:27 pm »

The Mackie 402 I own is small, sounds great, and sums to mono all channels if needed so that you can use a TRS-XLR cable in just one output, or send one to the house system and one to your GoSpeak. Outputs are balanced. For $99, great mini mixer.
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Re: Unbalanced to balanced (yes, this again)
« Reply #9 on: July 29, 2013, 04:18:27 pm »


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