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Drive Rack PA2 with QSC GX5 and GX7 having issues.

Krusty BadgerKrusty Badger Posts: 2
edited September 2016 in PA Configuration Wizard
Hi guys this is my first post here so I hope its in the right section.
Just bought a Drive Rack PA2

I started to go through the setup wizard and all was fine
I picked passive as I have 2 tops being powered by a QSC GX5 Power amp and I have my 2 subs powered with a QSC GX7
I don't have any speakers on the list so I picked not listed.
I have the RTA mic so I started to go through that part of the setup and it told me to set my QSC GX5 at 45% then it did a reading from the RTA Mic on the top left and Top right speakers.

It then said to set the QSC GX7 to 45% and it did its reading of the RTA and told me to increase the amp by 9db however by doing this almost uses the full amount of my power amp.

Now the thing is that my top speakers are rated at 400w RMS and 800w peak they are Peavey Black Widows the power amp is able to provide 500 watts per channel into 8 ohms and my speakers and I can confirm my speakers are 8 ohms but it would seem with the drive rack settings I'm only using 45% of that GX5 amps capability ?

However my subs are 1000w RMS and 2000w peak and the power amp for the subs is the QSC GX7 that can run at 750w per side at 8 ohms seem to be almost maxed out this I can't seem to understand.

Has it some how attenuated the power going to my GX7 power amp ?

The problem I'm faced with here is that I don't seem to be using all the available power when using the drive rack PA2.

When I run my tops and bottoms in series just using the GX7 using the built in crossover on the subs and no drive rack connected I can achieve a lot higher volumes than when using the drive rack and thats with my GX7 power amp only being at 50%

With that said using the Drive rack seems to be causing issues with how much output I am getting please can anyone advise why ?
No limiters active.

Also with it telling me to set the tops to 45% why is that when it docent know the power of the tops its going to ?


  • Options
    DraDra Posts: 3,777
    The attenuation knobs on the amp has nothing to do with the power of the amp. Here is what I mean, using made up values.
    The amp is rated for 500w @ 8 ohms. That is 63v. The amp's job is to take a lower voltage and amplify it, so for the amp to do it's job, a device (mixer, processor, etc) sends a lower voltage (usually between 0 and 3v, or so).
    If the mixer can send 1v of output before clipping, the amp may have to be set with no attenuation (full up) to output 63v.
    If the mixer can send 1.5v of output BC, the amp may only have to be set to 70% to output 63v. But if the amp is set to 100% in this case, the amp will clip as it tries to amplify a greater voltage than it is capable off.
    If the mixer can send 2v of OBC, the amp may be set to 50%.
    2.5v -> 30%, and so on.

    Most likely you are seeing a volume difference between with & without the PA2, based on the mixer fader positions or the meters. This just means the gain structure is out of whack.
    Go here viewtopic.php?f=61&t=959 and follow these steps to set the gain structure. The whole article is good info, but the specific steps start about half way down with the heading "GAIN STRUCTURE" and numbered steps below.

    If you have more questions or get stuck, post back.

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