Right, bought a QSC RMX2450 power amp...help needed.

[far0n]

Which of these dip switches should I be noodling with ? The plan was to run both channels with a single 8 ohm cab in each for now, maybe moving up to 4 ohms per channel later when I can afford it. Anyway, the chap wasn't sure what the wires did on the back, you'll see in the picture that the blue and brown wires are connected up. Is this running both channels in mono like this ?? All help & guidance greatly appreciated.

[ahpook]

disconnect the wires, make a brew and read the [url="http://media.qscaudio.com/pdfs/manuals/RMX_User_Manual.pdf"]manual[/url] and get your head round how it works.

if you're planning on changing the config later, you may as well get to know it properly.

Edited December 28, 2011 by ahpook

[icastle]

Get rid of those wires for starters - they were put there by someone who didn't read the manual.

Assuming you want to run the amp in mono through two speakers I'd start with this...

1= ON
2= ON
3= OFF
4= ON
5= ON
6= OFF
7= OFF
8= OFF
9= ON
10= ON

Signal goes into the Channel 1 input socket and is split over both amps equally.
Signal appears on both Channel 1 and Channel 2 outputs.
Volume controllable individually on both channels using the front controls.

EDIT - Keep the volume levels down low when you try it out or you might regret it.

HTH

Edited December 28, 2011 by icastle

[Monckyman]

+1 to above. Looks like a bodged bridge job in the original pic.
[url="http://www.qscaudio.com/pdfs/manuals/RMX_User_Manual.pdf"]http://www.qscaudio.com/pdfs/manuals/RMX_User_Manual.pdf[/url]

[icastle]

[quote name='Monckyman' timestamp='1325114879' post='1480060']
+1 to above. Looks like a bodged bridge job in the original pic.
[url="http://www.qscaudio.com/pdfs/manuals/RMX_User_Manual.pdf"]http://www.qscaudio....User_Manual.pdf[/url]
[/quote]

Looking at the way it's been left I'm guessing it was stripped out of a club or bar installation.

I think they wanted a stereo input for 'compatability' and a mono output for installation convenience but the DIP switches don't support both features at the same time.

[Musky]

At first glance I thought it had been bridged as well, but it's the inputs that have been linked. So perhaps they've been feeding it with a mono signal and using the link to feed both of the channels?

[far0n]

That's what I thought. Strange cos there's no need to do that really, you just flick it to parallel instead and hey presto.

Cheers for the manual, pretty self explanatory really

[far0n]

Oh yeah, paid £215 for it. Seems like a monster amp for the money !

[icastle]

[quote name='Musky' timestamp='1325145557' post='1480151']
At first glance I thought it had been bridged as well, but it's the inputs that have been linked. So perhaps they've been feeding it with a mono signal and using the link to feed both of the channels?
[/quote]

No it's the outputs that have been linked - the labelling on the back panel is quite poorly thought out and the 'Input' markings relate to the XLR connectors just to the right of the speaker outputs.

It threw me as well when I first looked at the photo and I only got my head around what was going on when I looked at the line drawings in the instruction manual.

[crez5150]

That amp has been bridged to run at full tilt.... the dip switches relate to each input and nothing to do with the output stage

[Count Bassy]

[quote name='crez5150' timestamp='1325179417' post='1480673']
That amp has been bridged to run at full tilt.... the dip switches relate to each input and nothing to do with the output stage
[/quote]
That's not how I would read it. IMHO it looks like they've just linked the two inputs together so that its working as two separate channels from the same signal (i.e. two channels mono). As someone has already said, they haven't read the manual (possibly didn't have one) as there are switches specifically to do that.
Not quite sure what the 'bridge' switches do here, unless they simply invert one input signal against the other so that the outputs are anti-phase to get the full voltage swing for bridge mode.

If in doubt RTFM.

[crez5150]

[quote name='Count Bassy' timestamp='1325437837' post='1483139']
That's not how I would read it. IMHO it looks like they've just linked the two inputs together so that its working as two separate channels from the same signal (i.e. two channels mono). As someone has already said, they haven't read the manual (possibly didn't have one) as there are switches specifically to do that.
Not quite sure what the 'bridge' switches do here, unless they simply invert one input signal against the other so that the outputs are anti-phase to get the full voltage swing for bridge mode.

If in doubt RTFM.
[/quote]

Those wires are actually across the output section, not the input section.... though the photo does make it look like it is..... but it isn't

[JakeBrownBass]

[quote name='crez5150' timestamp='1325526924' post='1483992']
Those wires are actually across the output section, not the input section.... though the photo does make it look like it is..... but it isn't
[/quote]

Are you sure?

Looking at the manual, it calls it a Barrier Strip Input & is only pictured when talking about inputs.

[crez5150]

[quote name='JakeBrownBass' timestamp='1325528270' post='1484029']
Are you sure?

Looking at the manual, it calls it a Barrier Strip Input & is only pictured when talking about inputs.
[/quote]

Just had a look at one the one I have..... it's a much older unit than the looks of this one..... It could be a barrier strip input as you say.... my one has the Barrier strip outputs on the left where this one looks to be.... So.... could be or not... :oS

[dan670844]

I have one it runs my TE SMX head, on mine the DIPS are the following, low cut filters two per channel at 30 hz and 50 the others Dips are for making channel one the master ie to bridge. I dont use them as I am using the SMX crossover ,channel A runs the low end and B the high, all filters are off on mine as I dont need that kind of rudimentry filter on such a complicated preamp. Note if you bridge, be very careful about powering on/off they are good cheap amps, with a soft start ,but the inrush current when you turn them on will quickly kill your speakers (the soft start isnt very good) mute your preamp and turn the volume on the qsc Off before switching on off, personally bridging I wouldnt bother with. The amp will deliver if I remember 800 watts or so at 4 ohms i.e RMS enough for gigging ! per channel. You Can run only one channel on these amps. I dont use it at all any more I used to run 4 x 1048H on mine ( mainly for show) haha. I have the manual somewhere if you would like it.

Edited January 10, 2012 by dan670844

[dan670844]

Sorry I fogot to say I think as someone else has said the inputs on your amp are bridged I.e the signal coming into channel A is also feeding channel B. Mine is a later model in which they did away with this.

[far0n]

Right had this a few weeks now. I'm running two 8 ohm cabs, one on each channel. But I'm finding this isn't loud enough, I'm at least having to turn the rig up full whack. I've read the manual and looked at bridging it, but it only mentons running one cab. Does only one channel work in bridged mode ? So would I have to link the two 8ohm cabs with each other to run them both in bridged mode ? Ta folks.

[LawrenceH]

[quote name='far0n' timestamp='1326636113' post='1499740']
But I'm finding this isn't loud enough, I'm at least having to turn the rig up full whack.
[/quote]

900 watts should normally be more than loud enough for anything, unless you're running tiny cabs, in which case it'll normally be more than enough to fry them! What are you using as a pre-amp to drive this? The QSC has an input sensitivity of 1.23V, it's possibly worth mentioning that a lot of bass pre-amps on the market can't actually supply this adequately. If you don't have an appropriate pre-amp then you are not getting full power out of the QSC.

[far0n]

[quote name='LawrenceH' timestamp='1326639687' post='1499792']
900 watts should normally be more than loud enough for anything, unless you're running tiny cabs, in which case it'll normally be more than enough to fry them! What are you using as a pre-amp to drive this? The QSC has an input sensitivity of 1.23V, it's possibly worth mentioning that a lot of bass pre-amps on the market can't actually supply this adequately. If you don't have an appropriate pre-amp then you are not getting full power out of the QSC.
[/quote]

See now, at 8 ohms each channel only puts out 450W. So I'm not really getting anywhere near the full load. I had a feeling this was the case, that the input signal wasn't strong enough. The amp seems to be perfectly fine, it's just quiet. Any recommendations for preamps ?

[LawrenceH]

[quote name='far0n' timestamp='1326646034' post='1499878']
See now, at 8 ohms each channel only puts out 450W. So I'm not really getting anywhere near the full load.
[/quote]
'Only'?! Didn't you say you were running 2 8-ohm cabs, ie 900 watts total? I have a similar PLX2450 for PA work, even into 8 ohms it is enough to shake down walls. The 1300 watts you'd get running the amp at 4 ohm bridged (ie two 8 ohm cabs run in parallel) won't actually make it significantly louder compared to 900 watts (two 8 ohm cabs, one on each channel), especially when speaker limitations/power compression is taken into account.

Before looking at new pre-amps do you have access to any mixing desks? Easiest way to check whether it's the amp or the pre that is limiting things is to DI into a desk that outputs around +4dB sensitivity, ie the correct sensitivity to drive your amp, and play through that. Even the cheap little Behringer numbers have enough to juice for your purposes (+/-18V supply on the one in front of me, for example).

Problem with a lot of guitar and bass pre-amps/pedals is that they don't operate at 'professional' standard output levels. PA stuff does, so to drive a PA amp properly you need the gear to match it.

[Monckyman]

What He said ^.