if you select a mono output, like out1, this will sum to mono, so you don’t need to add a mono block at the end of the chain
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Thank you for replying, now I’m confused, reading the other posts on here they suggest it does not sum to mono???
if you use the xlr1 connector, to ensure that the signal is mono you must select the out1 output. I suggest you take a look at the “setup examples” chapter of the manual and check for yourself using a typically stereo effect such as ping -pong delay
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For me, the confusion here lies in: If you send a stereo signal through a single output, you will hear what appears to be a mono signal coming from Out L or Out R, Out 1 or Out 2, respectively, in stereo speakers, i.e. studio monitors. If you then monitor the same signal through the same Output via headphones, you will hear the whole stereo field if the signal does not have a mono block (i.e. Single (M) Lite from the IR Loader) at the end of the signal chain before the output block, i.e. Out 1. Please test this out (using a ping-pong delay or whatnot) and let me know if I am incorrect, or if headphones simply receive a different signal than output speakers.
The output block is just like any other QC block when it comes to handling mono or stereo inputs. So if you put a stereo signal path into output 1 (or 3), the stereo path will be summed to mono in the output block. If you put a mono signal path into output 1/2, you will get a dual mono output.
You can easily test this by using a ping-pong delay. Set the delay time to some value, full stereo width and into output 1/2. Notice that the delay bounces from left to right in your speakers at the delay time.
Then change the output to just Out 1. Notice the delay is only in one speaker, but the delay time and repeats is the same as it was for stereo, it’s just not bouncing back and forth anymore. If Out 1 was only getting one side of the signal path and not summing to mono, the delay time would appear to be cut in half since you’d be missing the other side of the stereo path. The fact that this doesn’t happen demonstrates that Out 1 is summing its stereo input to a mono output, as we would expect.
If on the other hand, if you have a stereo signal path going into Out 1/2 and only have one cable plugged in, then this does not get summed to mono and you will only get one side of the stereo signal path. Again, depending on the effects, that might sound fine. It wouldn’t work well for a ping-pong delay because the delay time would appear to be cut in half. But it would probably be fine for a stereo reverb.
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yes, the headphone out being a different(stereo) feed from the main Outputs will lead to some major confusion. If you’re configuring all this on headphones you won’t hear an accurate representation of what’s really going on if you’re using single Output blocks or jacks.
for example (I just tested this):
if you use a stereo ping-pong delay and send it to Output 3 only, it sums to mono at output 3. However, in the headphones it will still ping-pong in stereo even though it shows the level from output 3 being monitored.
This could definitely cause confusion
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How I read this is: If you want mono output from a stereo chain select a single output not a pair. Does this mean if I want to send a mono signal from output 1 to FOH and output 2 to the monitor board, I can’t send a mono signal on both outputs?
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@bluzdog Now this is one I can answer; you can definitely send the same signal to both outputs. Its on Page 63 of the Manual. it shows using an A/B splitter to send the same mono signal to both outputs.
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That’s fine if you’re not already using that lane.
Ah so a splitter uses the entire Lane 2? Thats not good!
Yeah, that test is precisely what was confusing me, thanks a lot for clarifying this. I’m also noticing that monitoring options for the headphone jack are either 1/2, 3/4 or both, so there isn’t even a mono output option for headphones. Which I suppose means @jamsden was correct all along…
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So, confirming what’s been said on here but thought I’d try a setup for myself, nothing beats getting your hands on to learn how something works. Here’s what I did;
Took outputs 1&2 to two separate monitor speakers, i setup the lane output to 1&2 and put a ping pong delay at the end of the chain. The delay did exactly as expected, I heard the deley going from left to right. I then pulled the right XLR out of the QC and the delay effectively doubled in time, in other words I was only hearing one side so this is the first proof; the QC does not automatically Sum to mono when a plug is pulled (Other modellers switch from Stereo to Mono automatically in this scenario). So then, I changed the output to just OUT 1 and sure enough the ping pong delay went back to normal speed but only out of one side, so this proves that with Stereo effects into mono out you will get both L&R out of the one output. So for me, (apart from the fact it does not automatically sum to mono on connector removal which is no biggy for me) It does exactly what I want, and adding a splitter that outputs to OUT 2 as a mono duplicate of mono OUT1 even with stereo effects is perfect for enabling me to have a floor monitor and an output to FOH. Also means no need for a sum to mono block. However, there is one case where I can see sum to mono is really useful, when I don’t want to use an entire lane for my splitter, then use a sum to mono and output to 1&2; it will be mono in both so monitoring and FOH will get the same but you’ve used one block instead of one lane. I appreciate others have covered this already, It just helps clarify it for my own head and gives others the chance to tell me I’m wrong (or right!). What would be useful to complete my knowledge is if anyone knows this: If I use a mono block (say a simple delay) after a stereo block then is the mono block converting the stereo signal to mono? Would be useful to know as this way I could lose a sum to mono block
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yes…try it yourself with the ping pong trick 
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also, don’t forget you can use a Send block on the grid (if you’re not already using both fx loops) as an additional 1/4" mono output anywhere in an existing lane- no splitter needed.
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QC has out 1/2 and 3/4. I use 3/4 for my stage amp (Powercab) and 1/2 for FOH and IEMs. No need to deal with mono blocks to get out 1/2 to have the same content.
Out 1/2 and 3/4 are on different paths because I use Powercab in Flat/LF Raw mode without a cab block/IR in QC. This is effectively a powered guitar speaker and sounds better than FRFR and cab block to me, quite a bit better.