Balancing some signals

[Adam P]

My console's cue output comes on a stereo TRS jack. To plug it into my headphone amp I use a TRS to dual TS cable (your standard insert cable). I eventually want to get a snake to put in the tracking room and be able to place my headphone amp in there so the musicians can adjust their own levels. However, I don't want to run my unbalanced lines through 50 or 100 feet of snake cable, so I figured I could balance the signals first. I would just like to know what I'd need to do this. Do I just need to wire a pair of transformers up to some TRS jacks? Would an Ebtech Hum Eliminator work (I think its just a pair of balancing transformers)? Could I use a pair of passive DI boxes? Any other suggestions? I don't need million-dollar answers, either...they can be on the cheap. Please help me out if you can. Thanks.

[bennychico11]

well, ideally you'd just run a long TRS cable all the way to the tracking room...then split it at the box just like you're doing now.

however, the headphone signal is not a balanced signal. Remember, just because you are using TRS connectors, does not mean it's balanced. A balanced signal is determined by the gear you are using, not the cable. With the headphones you just have a Right signal and a Left signal on the two leads...and the ground. So no balancing is being done.
Just like you said, you're using a typical insert cable...and just like headphones, inserts are unbalanced as well.

an amp to speaker is going to be unbalanced

[punkin]

Good point...I've seen cheapie mic pre's with TRS jacks but inside the extra contact isn't used or shorted (Ring to Sleeve). I don't know why they do this except maybe they buy their parts in bulk and use the TRS jacks for other products or devices.

[Adam P]

Right, I understand that a headphone signal isn't balanced. I think you misunderstoood what I meant, which isn't surprising because I wasn't really that clear about it. Basically, right now I send unbalanced signals into my headphone amp which is in the control room, and use long headphone cables. In the future, I want to send the cue mix Left and Right signals on balanced returns on a snake, and place the headphone amp in the tracking room, far away from the console. But my console's cue mix outputs are unbalanced, so I want to balance them before sending them along the returns. In a nutshell, I want my headphone amp far away from the console, but don't want to run long unbalanced lines; I would prefer to balance them. Thanks, and sorry for the confusion!

[punkin]

To do that, I'm thinking the most practical way is to pass the signal through a transformer or other isolation device. The unbalanced circuit is often an amplifier output with it's return tied to ground.

audio amp (+) -------(speaker)-----audio amp ground

The balanced circuit usually looks something like this;

audio amp (+) -----(speaker)-----audio amp (-) not ground.


To get unbalanced to go unbalanced usually need an isolation device of some kind because a balanced circuit could be damaged when sent to ground if it's not designed to do this. I have seen devices which can handle either/or but you'll want to be sure.

Check these out;

http://www.lundahl.se/probsolv.html

http://66.102.7.104/search?q=cache:w...nsformer&hl=en

http://www.nullmodem.com/Audio.htm

http://bluejeanscable.com/articles/balanced.htm (go to the bottom of this page)

http://www.faqs.org/faqs/theatre/sta...ection-27.html

http://www.ians-net.co.uk/articles/balanced_lines.php (again at the bottom of the page)

[Adam P]

Hey, thanks, I appreciate the info. I'm not sure where the amplifier and speakers are coming into play, though, as the cue mix output is just a line level signal that's unbalanced, and which I would like to balance in between the console and the headphone amp, which has balanced inputs.

I did figure that I'd just need some sort of balancing transformer. I asked about the Ebtech Hum Eliminator, as I am pretty sure that its nothing more than a couple of balancing transformers in a little metal box. If that's the case, would one of those work for me, or should I pick up a couple of transformers and make my own?

Thanks again.

[punkin]

Sorry to confuse matters by using the speakers as examples but they're really just in the discussion to represent circuit loads. The concept is similar when talking about device other device input/output impedances.

You could try to make something but I suspect that by the time you found the exact tranformer to work for your application, built up some sort of housing, you'd be close to the cost and twice the aggrivation.

I'd start out by looking into the product manuals for both of your devices...look at the specs and give a couple vendors a call. One or two of the links I posted had actual product sources. Keep snooping the web...you're on the right track though.

What console are you using and what headphone amp?

[punkin]

I just had a quick look at my Behringer HA4700 headphone amp. It has an AUX and Direct in which accepts Unbalanced signals. The unit also has a Main inputs which accept Balanced connection. These things are pretty cheap, it might be worth looking into.

Which headphone amp are you using?

Am I helping or no?....It seems that you might be bent on making what you already have work.

[Adam P]

I'm using a Behringer headphone amp...4400 maybe? I don't recall which generation offhand.

Yes, you're helping, thank you. I'm afraid I've just made the issue too confusing through my wording and we're going around in circles or something. I do appreciate your help though.

[Adam P]

It's just an older version of your 4700. No EQ options on the channels, but pretty much the same otherwise. It does have balanced inputs. My console has unbalanced outputs. I want something to balance said console outputs.

[punkin]

Here's the link for the HA4400 manual. See page 15. It shows the same as the HA4700. The AUX and Direct IN's accept Unbalanced signals. The Mains accept 50k ohm Balanced and 25k ohm Unbalanced.

http://www.behringer.com/05_support/...A4400&lang=ENG

[punkin]

Oh!...I gotcha...that's why the discussion about your snake and cable lenghts...DOH!

Back to the transformer idea then...how about Radio Shack or similar

http://www.radioshack.com/product/in...tId=2062444&cp
http://www.radioshack.com/product/in...tId=2062443&cp

Or Lundal
http://www.lundahl.se/product_proces...form_list.html

Or Rane
http://www.rane.com/bb22.html

[Adam P]

Yes, thanks. Something like that Rane unit is what I'm after. I think the Ebtech might do the same thing, and then I wouldn't have to use RCA connections.

Thanks for your help.

[punkin]

yea, yea, yea...you were all over it from the get-go...the ticket is the isolation and proper impedance matching of the mixer output and the headphone in's.

I'm not familiar with the devices you're looking at but as long as it does the above and has enough drive it should work just fine.

Leave it to me to over complicate matters.

[Adam P]

No problem. I figured it would be a fairly simple solution, but its those seemingly simple solutions that make we want to double check things, to make sure I'm not overlooking anything. Looking at the literature for the Ebtech, which I probably should've done in the first place, indicates that they can be used to do what I'm looking for, so hopefully I can pick one up on the cheap from eBay, or borrow my buddy's.

[punkin]

Someone should just delete this whole thread now