Power Ampage

[Asyd309]

Here's one for all you techies out there.

I am running a Tech 21 RBI preamp into a QSC RMX 1450 power amp. I ultimately feel I am being overpowered by the combination of drums and two guitars, so I've decided to change how my power amp runs. I had it running in stereo - which according to the user manual, is approximately 450w per side. But still, I have to crank my output of the preamp and power amp to get anywhere near what I want for volume - but thats pushing it.

So I tried running the amp in bridge mono mode. Now, the way I understand it is I have to change the polarity in my cable for this to work correctly.

So I've changed the polarity in the output end of my speakon cable, but I can hear no noticable difference.

my cabinet is a Ampeg 610, capable of running 600 RMS @ 4 ohms, 1200 @ peak. Theoretically, my bridged mono connection should give me 1400w, which by my account is plenty of headroom. All I seem to get is alot of distorted clipping.

Would I be better off trading up for a larger cabinet, like the 8x10 because of it's better RMS handling , or is there a better solution ?

[neatobassman]

Tell your guitarist to turn down, just for the sake of your ears if you aren't using ear plugs. What's the second cabinet you are running?

[Asyd309]

There is no second cabinet. I'm not so much concerned with the guitar's stage volume as I am my own. I just feel like I'm not getting the most amount of power from my rig. I've stood in front of other bass rigs on stage and in a retail store where I've felt and heard what 600+ watts sounds like. I feel like I must be doing something wrong with my set-up, cable/wiring wise.

[edgebass5]

To make a QSC power amp run in bridged mono mode you have to do 2 things:

Step-1: You need to rewire the end of your speakon cable that is used for the power amp. You'll need a 4-pin speakon cable to start with. Make sure that the cabinet end of your cable is wired +1 (positive) -1 (negative). Now switch the wiring on the power amp end of the cable to +1 (positive) +2 (negative). Mark the cable so you always know which end is which. QSC power amps come with a great owner's manual (that can be found online) that have a diagram of the required speakon wiring for the different modes of operation. I suggest you confirm this wiring with the owner's manual, or the owner's manual on the QSC website.

Step-2: On the right hand side of the back panel of the power amp there are a series of dipswitches. Make sure that your switches are set for proper bridged mono operation.

Optional step: When you're adjusting your dipswitches try turning on the 50hz filter. This will keep everything under 50hz out of your output signal which is a GREAT way to eliminate seemingly useless, power-robbing low end from your signal and get more out of your amplifier. Its not likely that your cabinet can produce anything below 50hz in a useable fashion, so don't stress about the loss of low end. Its not likely you'll even hear it.

If after that you can't get enough volume out of an RMX1450 and a 6x10.... well..... Its time to look at your EQ and the stage volume of the rest of your band because something isn't right.

[Asyd309]

Edge, thanks for the insight.

I have the manual, and I've done everything you've described right down to a T, including using the 50 Hz filter. two days ago, I couldn't seem to make it loud enough. Last night I recheck all my wiring configuration and imputs and outputs - and boom - more power !! It seems to work, but I've also come upon a new problem - scratchy pots on my bass and input gain on the power amp. Small problems, I know but man I am I relieved.

And this morning, I got word that the neighbors want to petition the band from rehearsing. Apparently, we're too loud, and the bass rattles their window frames. Ha !

[edgebass5]

^^^Glad that worked out for you. Scratchy pots can be cleaned with a can of compressed air or some electrical contact cleaner. That or you can just replace them as they are VERY cheap.