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How do I link power amps together?


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I'm running sound at a small show on Friday (I have to leave by 3 PM ... please help me before then!). I don't feel like taking my set up that I listed in the other thread. This show only calls for vocals being ran through the system. I'm going to take my Mackie 406M 500 watt powered mixer. I direct all of my power to the Mains (it has a power routing switch that you can between Main/Main and Main/Monitor) and run a set of enclosures off of it. The mixer has only one Monitor Out line. I have two QSC USA 900s that I'm hopefully going to use to power two sets of monitors. How would I run these together into my one Monitor Out? I would imagine I have to somehow link the power amps together.

 

What mode would I need to put the amps into? What kind of cables am I going to need in order to "link" the amps together? I'd preferably like to pull this off without having to get a Y cord ... I'm not really going to have the means to pick one up before the show. If I REALLY have to, I suppose I can ... but life would be easier if I could pull this off without a Y cord.

 

Thanks in advance.

 

PS - If I do need to get a Y cord ... how much should I be looking to spend on this thing?

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Wow, that was simpler than I thought. So I would just run both of the power amps in stereo mode like I normally would ... but since I only have one Monitor Out ... I just need to use the Y adapter to throw them into the same jack?

 

Also ... side question ... the reason I need to use two different power amps is because whenever I tried to daisy chain 4 monitors into one power (in stereo mode) ... it would only come out of the two speakers that were plugged directly into the power amp. At the time, I would just knock the switch over to Bridged Mono and they would all start working ... however, I've recently been informed that the QSC USA 900s should NOT be ran as 2 or 4 ohms in Bridged Mono. Any idea why the daisy chained speakers would only work in Bridged Mono but not in Stereo?

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Wow, that was simpler than I thought. So I would just run both of the power amps in stereo mode like I normally would ... but since I only have one Monitor Out ... I just need to use the Y adapter to throw them into the same jack?


Also ... side question ... the reason I need to use two different power amps is because whenever I tried to daisy chain 4 monitors into one power (in stereo mode) ... it would only come out of the two speakers that were plugged directly into the power amp. At the time, I would just knock the switch over to Bridged Mono and they would all start working ... however, I've recently been informed that the QSC USA 900s should NOT be ran as 2 or 4 ohms in Bridged Mono. Any idea why the daisy chained speakers would only work in Bridged Mono but not in Stereo?

 

Do your amps have parallel mono input capabilities? As for your problem, no idea. What did you do to troubleshoot? It should have been pretty easy to narrow it down.

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Wait a second ... not as simple as I thought. The Y adapter would only work for running ONE of the power amps in Stereo mode into the one Monitor Out that is provided on my PA.


Am I going to have to utilize parallel mono to make this all happen?

What's wrong with using parallel mono if the amp has that capability? All it does is "Y" your two channels together for you.

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:idea:

Wow, that was simpler than I thought. So I would just run both of the power amps in stereo mode like I normally would ... but since I only have one Monitor Out ... I just need to use the Y adapter to throw them into the same jack?


Also ... side question ... the reason I need to use two different power amps is because whenever I tried to daisy chain 4 monitors into one power (in stereo mode) ... it would only come out of the two speakers that were plugged directly into the power amp. At the time, I would just knock the switch over to Bridged Mono and they would all start working ... however, I've recently been informed that the QSC USA 900s should NOT be ran as 2 or 4 ohms in Bridged Mono. Any idea why the daisy chained speakers would only work in Bridged Mono but not in Stereo?

Wait, how were you getting the signal over to the second input of the power amp when you were using it in stereo? If the signal wasn't getting to the input of that channel, obviously the speakers wouldn't give any output.

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What's wrong with using parallel mono if the amp has that capability? All it does is "Y" your two channels together for you.

 

 

There's nothing wrong with parallel mono (other than the fact that I haven't utilized it yet), I was just asking if that's what I was going to have to do to make things work. So basically, I'm going to have to run both power amps in parallel mono and THEN take the two lines from there and use the Y adapter to make it fit into the single Monitor Out on my powered mixer. I think that sounds about right.

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:idea:
Wait, how were you getting the signal over to the second input of the power amp when you were using it in stereo? If the signal wasn't getting to the input of that channel, obviously the speakers wouldn't give any output.

 

 

I ran the Monitor Out to my one power amp which was set in Stereo into Channel 1. I didn't have anything ran into Channel 2 because I didn't have a Y adapter at the time. I understand that obviously nothing was going to be going to the second channel considering it had nothing going into the input. However, even on Channel 1, the sound was only coming through the initial speaker that was coming from the output. The speaker in which was daisy chained off of the main speaker wasn't receiving any sound until I switched it to Bridged Mono.

 

I was planning on just running the 4 8 ohm monitors in Bridged Mono mode for the show tomorrow until I was told that these specific power amps can't handle Bridged Mono in 2 or 4 ohms. Bummer. Is this true for ALL power amps or just mine?

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There's nothing wrong with parallel mono (other than the fact that I haven't utilized it yet), I was just asking if that's what I was going to have to do to make things work. So basically, I'm going to have to run both power amps in parallel mono and THEN take the two lines from there and use the Y adapter to make it fit into the single Monitor Out on my powered mixer. I think that sounds about right.

Ya, except you keep talking backwards and it gets confusing. Maybe you are even confusing yourself.

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I ran the Monitor Out to my one power amp which was set in Stereo into Channel 1. I didn't have anything ran into Channel 2 because I didn't have a Y adapter at the time. I understand that obviously nothing was going to be going to the second channel considering it had nothing going into the input. However, even on Channel 1, the sound was only coming through the initial speaker that was coming from the output. The speaker in which was daisy chained off of the main speaker wasn't receiving any sound until I switched it to Bridged Mono.


I was planning on just running the 4 8 ohm monitors in Bridged Mono mode for the show tomorrow until I was told that these specific power amps can't handle Bridged Mono in 2 or 4 ohms. Bummer. Is this true for ALL power amps or just mine?

 

Ya, you won't find a power amp that will support 2 ohms bridged, not in the regular world. As for your problem, you must have something hooked up wrong. It doesn't make any sense otherwise.

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Forget the bridged mono thing... just forget it. You are a good examplemof why the bridged mono function should be left off of power amps.

 

Get an appropriately powered stereo amp such as a QSC RMX-1450 or 1850 and be done with it. Of course you will have to read the manual to determine how to set the dip switches.

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DO NOT run it in bridged-mono.

 

The USA900 does not have a parallel mode, and it doesn't have multiple inputs jacks per channel. But,. it does have barrier strip inputs that parallel the Neutrik combo XLR/1/4" jack. You could connect the barrier inputs with some jumper wires..+ to +, - to - on each amp. Then run the mixer monitor output to one amp's channel-1 input jack. Run a cable from the channel-2 input over to the second amp. All four inputs will be connected, no Y-cables needed, just a few feet of small gauge wire to jumper the barrier strips.

 

Be sure you understand what I wrote and ask questions if you don't.

 

Again, do not use bridged-mono mode here. Stereo mode, limiters engaged.

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"Then run the mixer monitor output to one amp's channel-1 input jack. Run a cable from the channel-2 input over to the second amp."

 

Do I put the cable from Channel 2 of amp A into Channel 1 or 2 of amp B? Just a side note ... would it be better to use XLRs or 1/4"s?

 

Also ... I've never heard the term barrier strip used before. I understand the concept of hooking them up, I think ... but what are these? What kinda cords am I going to need ... maybe that would help me figure out what the barrier strips are.

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"Then run the mixer monitor output to one amp's channel-1 input jack. Run a cable from the channel-2 input over to the second amp."


Do I put the cable from Channel 2 of amp A into Channel 1 or 2 of amp B? Just a side note ... would it be better to use XLRs or 1/4"s?


Also ... I've never heard the term barrier strip used before. I understand the concept of hooking them up, I think ... but what are these? What kinda cords am I going to need ... maybe that would help me figure out what the barrier strips are.

 

 

 

Either channel is fine, they're linked together with the jumpers on the barrier strip. Both amps are jumpered to connect their channel inputs together, and the cable connects them. You can use either a TRS (stereo) 1/4" cable, or an XLR. FYI, keep the jumpers as short as possible.

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