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Bridged mode for more power?

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Bridged mode for more power?

Postby christianmurphy » Fri Sep 23, 2011 3:24 pm

I have a QSC PLX2502, from the PLX2 series, which (from what I've heard) I really like the sound of. I had a chance to check it out when I first got it but a friend has borrowed my speakon cables!

Online it states @ EIA 1 kHz 0.1% THD the amp will produce 450w @ 8ohms per channel.
But in bridge mono it will produce a single 8 ohm load at 1500w.

Also states at 4ohms, it will do a single 2500w load. So by hooking my two (8ohm) main monitors in parallel, I'd be able to give them a LOT more power than I would in standard stereo mode? The speakon connections are classed as 2X speakon linked. I can't find a wiring diagram online, but my assumption would be this is a parallel connection?
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Re: Bridged mode for more power?

Postby Mike Stranks » Fri Sep 23, 2011 4:23 pm

Hi Christian

Yes; your assumption about running your two 8-ohm speakers in parallel in 4-ohm bridged mode is correct.

Assuming that you have speakers with parallel inputs/outputs, the easiest way of doing this will be to daisy-chain your speakers from the bridged output on the amp. To do this you have two options.

1) Make a cable with bare wire ends to a standard two-pole speakon. For the amount of power you'll be handling I'd suggest cable with each of the two cores at 2.5mm diameter. You connect the bare-wire ends to the two RED speaker screw connectors on the amp.

2) Get a 4-pole speakon plug and wire the same two-core 2.5mm cable to the +1 and +2 connectors on the plug (these will be marked in the plug). The other-end is connected to a standard speakon 2-pole plug - which will connect to the first speaker. IT'S VITAL THAT YOU IDENTIFY THIS CABLE AS A 'SPECIAL' AND WHICH END IS TO CONNECT TO THE AMP. The 4-pole plug then connects to the upper of the two speakon connectors on the rear of the amp.

The amp is not configured to let you use both speakon outputs (on the amp) in bridged-mode.

HTH Mike
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Re: Bridged mode for more power?

Postby christianmurphy » Fri Sep 23, 2011 5:55 pm

Slightly confused with 'Assuming that you have speakers with parallel inputs/outputs' is there a different type of input a speaker should have if it's to be used in bridged mode, wired in parallel?

So bare wire to red +/- connectors on amp, going to one of my monitors normal speakon inputs. (My speakers have INPUT and LINK, or HIGH and LOW for biamping). The LINK connection is on pins +1/-1. I just assumed this was the output for parallel connection, and I could run that to the Input on my other speaker with a standard 2 pin speakon. Going from the LINK on +1/-1 to the Inputs on +1/-1 on the other?

Sorry if I'm not quite getting this!
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Re: Bridged mode for more power?

Postby Mike Stranks » Fri Sep 23, 2011 6:27 pm

christianmurphy wrote:Slightly confused with 'Assuming that you have speakers with parallel inputs/outputs' is there a different type of input a speaker should have if it's to be used in bridged mode, wired in parallel?
Forgive my terminolgy... what I meant was that your speakers have two connectors on the back that are wired in parallel... and yours clearly have, although designated INPUT and LINK. So no special connector required.

So bare wire to red +/- connectors on amp, going to one of my monitors normal speakon inputs.
Yes

(My speakers have INPUT and LINK, or HIGH and LOW for biamping). The LINK connection is on pins +1/-1. I just assumed this was the output for parallel connection, and I could run that to the Input on my other speaker with a standard 2 pin speakon. Going from the LINK on +1/-1 to the Inputs on +1/-1 on the other?
Spot-on! Give the man a cigar! :D

Sorry if I'm not quite getting this!
... but you are! :D
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Re: Bridged mode for more power?

Postby christianmurphy » Fri Sep 23, 2011 6:39 pm

Great :lol: Only thing I'm still a bit unclear on is you said I should use a 4 pin speakon using the postive of 1 and positive of 2, but I can't see how that would deliver a signal to the input of the speaker which uses positive 1 and negative 1.

Thanks for your help Mike :)
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Re: Bridged mode for more power?

Postby Mike Stranks » Fri Sep 23, 2011 7:28 pm

christianmurphy wrote:Great :lol: Only thing I'm still a bit unclear on is you said I should use a 4 pin speakon using the postive of 1 and positive of 2, but I can't see how that would deliver a signal to the input of the speaker which uses positive 1 and negative 1.

Thanks for your help Mike :)
OK; That was Option 2 if you didn't want to use the Option 1 "bare-wire" approach which we've amplified in the last couple of posts.

I've not read the manual - only looked at the pictures :D - but it looks as if the upper-most speakon connector on the amp is triple-purpose. That is:

1) By using a 2-pole speakon and using +1 and -1 then it's a 'conventional' speakon output for channel 1.

2) By using a 4-pole speakon and using +1 and +2 then you're connecting to the bridged ouput.

3) By using a 4-pole speakon and using +1,-1 and +2,-2 you can get channel 1 AND channel 2 from the one 4-wire connector. (I had an amp that had ONE 4-pole speakon output and you accessed the two channels as I describe here.)

So the option I've suggested as an alternative to the red 'bare-wire' terminals is No. 2 here. I think you'll appreciate that because the speaker itself is expecting a 2-pole +1, -1 connection - and you'd put a 2-pole plug wired accordingly on the OTHER end of the speaker cable that's why, if you make up a lead to handle this, it's important that you know which is the 4-pole end and which the 2-pole. [So your speaker lead for 'bridged' would be 4-pole +1 and +2 to connect to the amp and 2-pole +1 and -1 to connect to the first speaker INPUT. (And then a 'normal' 2-pole speaker lead from the LINK out to the other speaker INPUT.)]
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Re: Bridged mode for more power?

Postby christianmurphy » Fri Sep 23, 2011 7:55 pm

Got it. Fantastic advice as always. Thanks Mike!
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