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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => Installed Sound/Contracting => Topic started by: Peter Kowalczyk on November 03, 2020, 10:14:36 PM

Title: Balanced -> Unbalanced and CMRR
Post by: Peter Kowalczyk on November 03, 2020, 10:14:36 PM
I have a situation where I need to take an unbalanced -10dBu signal and send it across a building to another unbalanced input.  250' or less, probably more like 150'. 

I had planned to use a passive Summing / Balancing box at the source end, and another Balanced -> Unbalanced device at the receiver end.  The Audio Control BLX-10 transciever looks like it would do the job, but it doesn't appear to be available anywhere. 

It occurred to me that I could just take one leg of the balanced signal at the receiver, but then I realized that this would negate any possible CMRR benefit from using a balanced line. 

Then I started wondering if ANY *passive* balanced -> unbalanced receiver would give a CMRR benefit.  My instinct says that it wouldn't; you'd need an active receiver for that. 

What would you use?
Title: Re: Balanced -> Unbalanced and CMRR
Post by: Mike Caldwell on November 03, 2020, 11:18:39 PM
Look at Radio Design Labs aka RDL.
They have a quite a few unbalanced to balanced interfaces/converters both passive and active and
balanced to unbalanced interfaces.

I would look at using an active unit at the sending end and a passive unit at the receiving end.
Title: Re: Balanced -> Unbalanced and CMRR
Post by: Keith Broughton on November 04, 2020, 06:23:39 AM
I have done something similar with a Rapco Isobox at each end.
It's a transformer so you maintain CMMR over the long distance run and just wire the in and out sides for an unbalanced line. (short pin 3 to pin 1 and use 1 and 2)
Title: Re: Balanced -> Unbalanced and CMRR
Post by: John Roberts {JR} on November 04, 2020, 08:26:47 AM
+1 transformers

JR
Title: Re: Balanced -> Unbalanced and CMRR
Post by: Ivan Beaver on November 04, 2020, 08:37:49 AM
One thing you need to be a little concerned with is the level.  Small transformers will saturate with higher levels.

Look for a +4 dBu transformer and you should be fine.

I used to have a pile of old Altec octal plug in transfomers that I have used in all kinds of situations regarding unbalanced to balanced and vice versa configurations.  They always did the job.

Peavey used to make them also for the balanced inputs into the older amplifiers.

Just don't use a mic level transformer.

Transformers are also good, because the provide physical isolation.  A VERY GOOD thing.
Title: Re: Balanced -> Unbalanced and CMRR
Post by: Steve-White on November 04, 2020, 04:21:18 PM
Source Active > Destination Passive
Title: Re: Balanced -> Unbalanced and CMRR
Post by: Ivan Beaver on November 04, 2020, 06:20:32 PM
Source Active > Destination Passive
Why?  With decent quality transformers you should very little loss.

But there is nothing wrong with your statement.  To me, the big thing is having physical isolation at either end
Title: Re: Balanced -> Unbalanced and CMRR
Post by: Mike Caldwell on November 04, 2020, 07:22:25 PM
Source Active > Destination Passive

In my original post I was thinking that same thing just to bump up the level. At the destination/input end
a good ole fashioned transformer.

That all said a couple hundred feet is not that far and we send a much lower level mic signal that far
down a snake cable all the time or maybe not so much now in the world of digital.
Title: Re: Balanced -> Unbalanced and CMRR
Post by: Peter Kowalczyk on November 04, 2020, 08:07:17 PM
Thanks Gentlemen,

Yes, transformers!   I had planned to use an Edcor S2M passive transformer device to sum and balance the signal at the source.   https://www.edcorusa.com/s2m.  I have one left over from another job where I bought two and only needed one.  It worked great there.

@ Mike Caldwell - I've used a lot of RDL's little problem solvers before.  I've put a dozen or so of their D-J series Decora input modules in various jobs, including this one.  In fact, the unbalanced source I'm working with is the 'Pre-Amp Out' of their HD-MA35U utility amplifier.  I think I'll get a TX-A2 to use at the receiver.  https://www.rdlnet.com/product.php?page=504

Thinking more, the CMRR behavior of a transformer at the receiving end is obvious.  Duh. 
Title: Re: Balanced -> Unbalanced and CMRR
Post by: Steve M Smith on November 05, 2020, 03:17:13 AM
Peavey used to make them also for the balanced inputs into the older amplifiers.


Yes. those Peavey transformers are actually qhite good. I have used them in a few things.




Steve.