Amplifier using multiple inputs

[KBToys82]

Hey everyone, I have a really stupid question.

I have 2 QSC GX5's powering my front and rear speakers in my auditorium and a GX3 powering my floor monitors when I need them for our school auditorium. We use a Mackie mixer in the BOH for our simple sound needs, but for our more advanced stuff like the talent night and plays, I use a Presonus StudioLive 32.4.2 AI mixer wired to a different BOH mixer (PreSonus RML32 AI.) Since we only use 1 setup at a time, is it possible to keep both connected to our amps, 1 via XLR inputs and the other using 1/4" TRS? Even should the unimaginable happen and I accidentally leave some channels open on the Mackie, would this harm the amps?

Thanks!

 

[RonHebbard]

Hey everyone, I have a really stupid question.

I have 2 QSC GX5's powering my front and rear speakers in my auditorium and a GX3 powering my floor monitors when I need them for our school auditorium. We use a Mackie mixer in the BOH for our simple sound needs, but for our more advanced stuff like the talent night and plays, I use a Presonus StudioLive 32.4.2 AI mixer wired to a different BOH mixer (PreSonus RML32 AI.) Since we only use 1 setup at a time, is it possible to keep both connected to our amps, 1 via XLR inputs and the other using 1/4" TRS? Even should the unimaginable happen and I accidentally leave some channels open on the Mackie, would this harm the amps?

Thanks!

The first thing that strikes me is the XLR & TRS inputs on your amps will be connected in parallel thus the output of each mixer will be attempting to drive back into the output of the other. Outputs driving into other outputs is NEVER a good thing. To answer your query, no I don't believe this will harm your amps. Your mixers maybe but not your amps.
Toodleoo!
Ron Hebbard.

 

[KBToys82]

I'm not too familiar with what a passive setup, but my Mackie Mixer has 2 sets of main outs. The XLR out goes to 1 amp, and the TRS out goes to the other amp.

 

[RonHebbard]

I'm not too familiar with what a passive setup, but my Mackie Mixer has 2 sets of main outs. The XLR out goes to 1 amp, and the TRS out goes to the other amp.

In your original post I thought you were asking if having multiple mixers simultaneously connected to your amps would harm your amps. To which I replied that your amps wouldn't mind but your mixers very well may. Perhaps I've misunderstood your query.
Toodleoo!
Ron Hebbard.

 

[FMEng]

I'm not totally following this. Are you trying to Y connect the two mixer outputs together?

 

[KBToys82]

So what I was thinking of doing is having my regular mixer go into the TRS inputs on the amps and have the PreSonus rack mixer which only gets used for special occasions plugged into the XLR inputs. The only chance I can think where 2 mixers would be sending sound at the same time is if I forget to zero out my rack mixer.

 

[RonHebbard]

So what I was thinking of doing is having my regular mixer go into the TRS inputs on the amps and have the PreSonus rack mixer which only gets used for special occasions plugged into the XLR inputs. The only chance I can think where 2 mixers would be sending sound at the same time is if I forget to zero out my rack mixer.

Whether they're simultaneously sending signal or not, the problem I'm seeing is your two mixers would not only be driving the amps inputs but also driving into each others outputs too and this is what I'm flagging as a potential problem.
As I wrote previously, I don't see this being harmful to your amplifiers but I do see it as potentially harmful to one, or both, of your mixers. What say you @FMEng?
Toodleoo!
Ron Hebbard.

 

[FMEng]

So what I was thinking of doing is having my regular mixer go into the TRS inputs on the amps and have the PreSonus rack mixer which only gets used for special occasions plugged into the XLR inputs. The only chance I can think where 2 mixers would be sending sound at the same time is if I forget to zero out my rack mixer.

That's not a good idea. The two jacks for each channel on the amp are wired together in parallel, which would cause the output of one mixer to be loaded by the output impedance of the other. That could result in distortion or low frequency roll-off. It's electrically the same situation as the thread, https://www.controlbooth.com/threads/mixer-outputs-wired-together.41499/

There are better ways to achieve the same result, if you are good with a soldering iron.

 

[JD]

You may actually damage one of the mixers. Most mixers have output protection to assure a reverse static pulse doesn't damage the output. This is in the form of low-current diodes that are wired in reverse from rails-to-outputs-to-ground. All well and fine, except when the mixer is turned off. When the mixer is off, the rails and ground are all at the same potential, which means a signal driven into the output from the other mixer will try to forward conduct the diodes, which are usually very small and sometimes integrated into the output IC. If you manage to pop one, you are in for a major headache.

 

[KBToys82]

Although parallel wiring still escapes me, I get it. I'm halfway debating just plugging the outputs of one mixer into the other, however since I'm not the only one who uses the sound system, it has to be a set it and forget type setup. No one wants to bother with finding out how to use the system.

 

[Amiers]

Make some kill switches for your your outputs but the problem is if they forget to turn off the switch and you turn on the other one well as everyone else has said that won't be good for the mixers.

 

[RonHebbard]

Make some kill switches for your your outputs but the problem is if they forget to turn off the switch and you turn on the other one well as everyone else has said that won't be good for the mixers.

Or you might entertain a D.P.D.T., break before make, switch selecting which source feeds the amp but then you'd need to be careful with how you terminated your shields to avoid ground loops and associated hums. How complicated can we make this for you? Just watch us, we can get you in over your head in just a few hours.
All the best.
Toodleoo!
Ron Hebbard.

 

[Moose Hatrack]

Maybe a pair of stick ons in the rack to mix the mixers?

 

[Dionysus]

Although parallel wiring still escapes me, I get it. I'm halfway debating just plugging the outputs of one mixer into the other, however since I'm not the only one who uses the sound system, it has to be a set it and forget type setup. No one wants to bother with finding out how to use the system.

I definitely lean towards just leaving one mixer connected, and feeding the outputs of the others into the first for you and your situation.

There are several things you could do otherwise however they indeed involve more and experience and knowledge than you seem to have. Hope everything goes well!

 

[RonHebbard]

Maybe a pair of stick ons in the rack to mix the mixers?

Exactly! Perhaps a little something from RDL. (Anything but having two sources driving into each other.) Break some of the rules but not too many at the same instant. [Shut up Ron! Stop typing and get back in your hole.]
Edit: Eliminated a redundant word.
Toodleoo!
Ron Hebbard.

 

[TimmyP1955]

Just build a summing box. http://www.rane.com/note109.html

 

[RonHebbard]

Hey everyone, I have a really stupid question.

I have 2 QSC GX5's powering my front and rear speakers in my auditorium and a GX3 powering my floor monitors when I need them for our school auditorium. We use a Mackie mixer in the BOH for our simple sound needs, but for our more advanced stuff like the talent night and plays, I use a Presonus StudioLive 32.4.2 AI mixer wired to a different BOH mixer (PreSonus RML32 AI.) Since we only use 1 setup at a time, is it possible to keep both connected to our amps, 1 via XLR inputs and the other using 1/4" TRS? Even should the unimaginable happen and I accidentally leave some channels open on the Mackie, would this harm the amps?

Thanks!

Perhaps it may help you to think of it this way: Your amps don't have multiple inputs per channel, merely different types of connectors all leading to the same input.
Toodleoo!
Ron Hebbard.