We are are using a separate broadcast sound mix through one of the mono mix outputs which are XLR on our board.
Good. The PA mix is usually terrible for anything besides the PA. Lots of people don't realize that, likely I think because they assume that *all* the sound in the room is coming from the PA, which it most definitely isn't!
I don't believe there is an option for one of the monitor mixes to be sent via an unbalanced output.
What board is it? Maybe a trip through manual could turn one up.
The intent is to allow the mono signal be received by both L and R in OBS so that anyone listening on earphones can hear the same signal in both ears.
If your entire rig is mono, then you can set OBS to mono as well. Settings -> Audio. That'll move the output problem up to the input side of OBS instead. You haven't solved the problem yet, by doing that, but you've moved it where you can see it better, which makes it a little bit easier to solve.
Why does our system work to send a mono signal to both L/R on iPhones and desktop/laptop PC computers but not on Android phones?
It's not "a signal" that is sent to both sides. It's a miscommunication because of the adapter, that results in what the rest of the system treats as *two* separate signals. One is sent to the left only, and the other is sent to the right only.
The system doesn't know that those two signals are exact opposites of each other. They're not the same; they're opposite. No difference at all in how they sound, but when you put them together, you get nothing.
The same actually happens in the air between the two speakers, but there's often enough unequal acoustics going on that it muddies things up to where you don't notice as much.
To allow this to work correctly I will need to make a modification as you indicated to our XLR mono mix output. From the A&H manual for the mix output:
"Professional equipment provides 'balanced' connections for maximum interference rejection over long cable runs. If you are connecting to 'unbalanced' equipment then make sure the XLR pin 3 (signal cold) is linked to pin 1 (signal ground)."
That's...incomplete at best. Is it signal balanced or impedance balanced? The manual should say somewhere. If it's signal balanced, is it floating or not? If so, is it transformer floating (probably not: that's the best possible compatibility but really expensive, so it's usually not done) or electronic floating?
The answers to all of that, determines the best way to wire it. A blanket statement like you quoted is not enough. If that's really all that the manual says, then A&H is really slipping!
For what it's worth, I have one of these in a standalone youth center:
User Guides, Software, Drivers and Documentation
www.allen-heath.com
I put some metal straps on the end caps to hold it slightly off the desk, with a single bolt in each end of the meterbridge to act as a hinge, so I can flip it up in-place and work on it with everything still plugged in, and in some cases powered on, with real signals. I keep the bottom covers off for the same reason; they're stacked against the wall instead.
The top-right corner of pages 13 and 14 of the schematic, and the right side of page 16, show the electronic floating balanced outputs. Like the transformer version, the signal always appears as a difference between the two wires, with the less-restricted one having more "swing". So if you leave one disconnected, then most of the signal will appear there and not on the one that *is* hooked up. That's why it says to ground the unused one for unbalanced operation.
BUT! Unlike a transformer, each output of an electronic floating output is still limited to the supply rails:
- If you leave one disconnected, it'll take most of the signal until it hits that limit, and then the other one will be forced to take over. This happens almost instantaneously, well within the wave itself, and consequently sounds terrible!
- If you ground the unused one, then the other takes all of the signal, so then it sounds like it's supposed to, but you lose half of the total swing, which translates to 6dB of headroom. Remember that, when you watch the meter on the board: the electronic floating output driver may clip about 6dB before the meter says it is.
My board does have some impedance balanced outputs as well, but they're harder to find on the schematic. They just tack a resistor onto an existing internal signal somewhere, and the other end of that resistor goes to the positive ("hot") wire in the jack. The matching resistor from the negative ("cold") wire to ground is on a different page of the schematic.
(it's a terrible example of how to lay out a schematic to be easy to read, but everything is technically on there)
Can I modify the XLR cable out of the board to link pin 3 to pin 1, and if so can you guide me?
I appreciate your expertise to help this rookie.
I would not modify the board at all, unless you're really, absolutely sure that you (or the next user) are never going to need the original functionality from it. Always modify the cords if possible, and only when not, think about changing the board itself.
I *have* modified several boards, but as I'm sure you can imagine, there's a lot more going on in there than there is inside the connector for a single wire!
Back to what I said earlier in this post, the reason to know what type of output you actually have, is because there's no universal way to make a passive balanced to unbalanced converter that is compatible with all of them. For example, if your balanced outputs are not floating at all, but actively drive both wires independently, and you ground one side of it, then that side of the output driver may eventually blow up. You may or may not hear a difference, but if it later ends up driving a 100' snake to stage for a different use, that's going to pick up a ton of noise because it's not actually balanced anymore.
