Tony, thanks for the response,
We are using SM 58 and 57 mics, I am running the 5th mic (a SM57) through the mono jack of the 5/6 channel.
A microphone has less output than an Instrument (Guitar/Keyboards for example) but if it's working for you it's OK to use the 5/6 channel.
I have been running the piano, a Roland RD300NX, through the 11/12 channel as a stereo signal, out of habit I guess. I don't think running it mono will compromise any tones.
Running the way I suggested is what the inputs and outputs L/MONO are designed for. It also saves on cable connections.
Regarding the use of Channel 1 for microphones panned hard to one side, and channel 2 for instruments panned hard to the other side:
This is one of the possibilities I meant when I wrote this:
There are one or two ways of connecting a mixer carrying different types of signal to the Compact.
I would have suggested this in my first post, but I didn't know how you were connecting the 5th microphone. You may have been using Channel 1 on the Compact for the 5th microphone.
If you do pan the mics hard to one side and connect that output to the Microphone channel of the Compact leave the EQ'ing of the mics until you see how the Channel Preset (you can't turn it off) on channel one works with your mics. You might not need to do anything else with EQ. If you do, you can adjust to preference. Using this way I'd pan the microphones to the Right (you're probably going to be using an L/MONO input for the Piano and that will be Left anyway).
You'd then pan the instruments to the left and connect this output via TRS - TRS to channel 2 set to line.
Another way to connect would be pan everything hard left and connect this output via TRS - TRS to channel 2 set to line. You could then connect the SM 57 (guitar) to channel 1 and give it the benefit of having a real microphone preamp.
Your suggestions/thoughts regarding the use of the 3.5mm input on channel 2 isn't a way that I'd even consider going especially not for a microphone as this would limit how loud you can run channel 2 (only until the microphone starts feeding back.
Keep it as simple as you can. You've got enough inputs on your mixer for everything that you're wanting to use (with maybe the exception of the SM 57 but that seems to be working for you). Using the other inputs on Channel 2 for instruments complicates things and I'd only use them at a pinch.
1: panning mics hard right and then to channel 1 and the instruments hard left and then to channel 2 set to line OR
2: Everything panned hard left and then to channel 2 set to line, with the SM 57 going directly into Channel 1 (which is the way I'd probably go).
The less complicated you make it, the easier it is to keep it under control.
Now I'd like to speak to this as ST has asked how old your system is, and I think he's trying to cover the possibility of the Compact maybe having some kind of defect (which I've not covered up to now):
As for the loudness, the L1 system has more than enough volume for the small venues we play, its just that this past weekend the volume would fade completely out then rapidly re-appear. At the time this was happening I was using both L/R mains, from the 1202 mixer, to the RCA jacks, not that I expected a stereo sound but it appeared to be the only solution at the time in order to not have to use a Y adapter to combine (rather than use an adapter to split) the signals which I was trying to avoid. I haven't even considered only using one side of the Mains with the channels on the 1202 mixer panned hard left.
What sometimes happens when you put the left and right signals of a stereo source together is that noise cancelling can happen. I'll try to explain this as simply as I can:
Imagine having 10$ in one hand and a bill for 10$ in the other hand. Put together your assets are zero. With a stereo signal being summed to mono by just connecting them directly together something similar can happen. Sometimes the 2 signals are 180° out of phase with each other, which means that where one of them has a positive value, the other has the same value but negative. When these two come together for the same source the volume will drop (fade). I'm not saying that this is what happened, but it may be what happened.
If you have the chance to set up and play in a gig sized room I'd try out the suggestions I've made here to see if the unit is working OK (the same room would be even better as you'd have many of the things the same as at the gig, but if not that's OK too). If everything works as it should do, then you've probably solved the problem. If not, then it may be time to call Bose. I think that this is probably why ST asked about the age of the unit to see if it was still under guarantee.
Regarding your music. Would you like to tell us a little bit about it (we can sometimes be a nosey bunch here ). You don't have to tell us, but if you'd like to I for one am all ears. Thanks.
With regard to this:
Please accept my utmost appreciation for your time and advice.
You're more than welcome to any help or advice that we can give you on the forum.
I hope that this has been of some help. If the unit still persists to fade in volume it may need looking at.