Dual balanced (or unbalanced) outs on a BA?

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poserp
Posts: 40
Joined: Thu Mar 08, 2007 10:11 am
Location: Los Angeles, California

Dual balanced (or unbalanced) outs on a BA?

Post by poserp »

I'd like to know if there's a way to add a second balanced or unbalanced output to a Baby Animal premap. Ideally, I'd like both outputs to be balanced or unbalanced (so there's no difference in output level between the two jacks). Thanks!

chrisp
Posts: 184
Joined: Sun Mar 04, 2007 11:46 am
Location: Sydney, Australia

Re: Dual balanced (or unbalanced) outs on a BA?

Post by chrisp »

Ok, first of all, there doesn't have to be a difference in signal level between balanced and unbalanced - this is a common misconception due to the fact that the default +4dbu connection for "pro" gear is usually TRS or XLR balanced outs, while the -10dbv connection for "consumer" gear is typically RCA unbalanced. However, it is entirely possible to have a +4db or hotter unbalanced signal. Its better to think of balanced signals in terms of radio frequency rejection ability (the balanced 3 wire signal separates sig- from ground, whereas unbalanced 2 wire uses the one wire to represent both) rather than as a signal strength.

Rant over. Are you using the JLM 1:1:1 output tranny - its ridiculously easy to do it if you are, you take separate windings to separate outs (windings 2+ and 2- to XLR1 pins 2 and 3 respectively, and windings 3+ and 3- to XLR2 pins 2 and 3 respectively, assuming you have winding 1+ to the PCB sig out and 1- to the PCB 0v).This uses the tranny as a true 1:1:1, and so is a 6db signal drop compared to the "standard 1:2" output schematic (where winding 2- is linked to winding 3+), but that usually isn't too much of an issue, given many run the BA without any output tranny at all.

If you want unbalanced, simply run the -winding to the ground lug of the output jack (TS or RCA). If you want unbalanced -10dbv, you'll need a 11.8db pad across the output.
Chris P
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I do lots of things. I believe eclectic skills are best.

poserp
Posts: 40
Joined: Thu Mar 08, 2007 10:11 am
Location: Los Angeles, California

Re: Dual balanced (or unbalanced) outs on a BA?

Post by poserp »

Thanks -- I asked about levels because I've seen several pieces of gear that offer an unbalanced output at 6db down from the balanced output, usually because there's a transformer on one and not on the other. Thus, I presumed that would be the "easy" way to do it. I don't really care about driving long cable runs; all the outputs will be wired within a rack so balanced/unbalanced doesn't really matter to me noise-wise. If, however, with the JLM 1:1:1 I can get dual balanced outs then that's all the better and I'll wire it up balanced. I presume that wiring it balanced the way you describe will result in both signals being in phase, correct?

Incidentally, can you run the 1:1:1 "backward" (i.e. take two signals in, one on 2+/- and the other on 3+/-) and use it as a 2-into-1 mixer? If so, it might be interesting to try wiring 6 of them together to make a simple 4-into-2 stereo summing circuit. I wouldn't expect a really clean signal out of that arrangement, but the "character" imparted by using that much iron might be nice.

chrisp
Posts: 184
Joined: Sun Mar 04, 2007 11:46 am
Location: Sydney, Australia

Re: Dual balanced (or unbalanced) outs on a BA?

Post by chrisp »

poserp wrote:I presume that wiring it balanced the way you describe will result in both signals being in phase, correct?
Yep.
poserp wrote:Incidentally, can you run the 1:1:1 "backward" (i.e. take two signals in, one on 2+/- and the other on 3+/-) and use it as a 2-into-1 mixer? If so, it might be interesting to try wiring 6 of them together to make a simple 4-into-2 stereo summing circuit. I wouldn't expect a really clean signal out of that arrangement, but the "character" imparted by using that much iron might be nice.
You can run transformers as mixers, yes - I have a set of mic-level Sowters that do all the mid-side decoder mixing - but they generally have to be designed to do that, taking impedance into account. Also you can't really go very far down that line, as the transformers need a loading to work, so you can't really daisy chain them too much. Its far better (and cheaper, frankly) to wizz up a couple of JLM hybrids in class A and use them as virtual ground summing opamps. That way you can get a lot more than 4 into 2, and you get a really nice summing box.
Chris P
---------------------------------------------------------
I do lots of things. I believe eclectic skills are best.

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