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Alembic Club » Alembic Basses & Guitars » Archive through March 01, 2013 » Using My F1-X with a QSC PLX 1804 Amp In Full Range Mode « Previous Next »

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Senior Member
Username: ajdover

Post Number: 1004
Registered: 11-2003
Posted on Tuesday, November 20, 2012 - 4:52 pm:   Edit Post

Got a question I need some help with.

I have an F1-X and a QSC PLX 1804 power amp. Currently, I biamp it into a 2X10 and 1X15. I want to try running it full range. I looked up the specs on the PLX 1804 at the QSC site, and their manual states that I can bridge the two channels using a jumper cable between the two input channels on the back panel, and connect the Channel 1 input to the output of the F1-X. Only problem is I have two 1/4" input jacks and two XLR input jacks (female) on the back panel. What this means is I can use either a 1/4" cable as a jumper, or an XLR - XLR cable as a jumper if I'm reading this right.

My question is this: Do I need to have a special cable to go from the F1-X to the XLR input on Channel 1 of the QSC? Is the full range output on the back of the F1-X stereo or mono? Doing the jumper between the channels is no problem with 1/4" jacks, but I'm trying to determine if it is possible to bridge it at all - I don't want to have to buy a new power amp if I can avoid it. Any and all input will be very appreciated.


Senior Member
Username: sonicus

Post Number: 2720
Registered: 5-2009
Posted on Tuesday, November 20, 2012 - 5:43 pm:   Edit Post

The Full range output on the F1-X is mono
Senior Member
Username: dfung60

Post Number: 573
Registered: 5-2002
Posted on Tuesday, November 20, 2012 - 6:30 pm:   Edit Post

Alan -

I took a quick look at the manual.

When you do the trick with the jumper, you're not actually bridging the amp, you're doing a parallel input into both channels. This means the same signal goes into both channels, which are operating independently in parallel and comes out in the two outputs. If you had two cabinets, then you would hook one cab to each channel and you could control the blend between them by using the input level controls on the front of the amp.

You can use a stereo 1/4" to stereo 1/4" cable to jump or XLR to XLR, but they're both unusual cables because they're the same gender on each end.

If you want to minimize the number of weird cables to buy/build, then I would create an XLR-XLR jumper and you can use a regular (mono) 1/4" cable from the mono full range out of the F1-X to either 1/4 input on the power amp. The F1-X doesn't have a TRS output, and the 1/4" jacks are designed to take a balanced signal, so it woudn't be compatible anyway.

The more feature-rich QSC has true bridging selectable by switch which is a little different than the parallel input setup that the jumper gives you. In bridge mode, the "+" side of your signal is fed to one amp and the "-" side to the other, so the two amps are actually being combined into one. This increases the power of the one channel beyond the sum of the power of the two channels (this is as if the speaker impedance had been reduced). The amp is then only one channel, and you only connect to one speaker jack. You can't easily do this without modifying the circuitry inside the amp.

For what it's worth, I've always liked the results of running my rig in full-range mode, whether bridged or paralleled. For a bass amp, even the high treble is every other instrument's low end, so you don't get the kind of win by splitting the sound as you do in a PA system where you are driving wildly different speakers for highs and lows.

Hope this helps,

David Fung
Username: willgunn

Post Number: 64
Registered: 2-2007
Posted on Tuesday, November 20, 2012 - 6:32 pm:   Edit Post

You could also run a standard XLR-type mic cable from the F-1X's front panel D.I. output to the XLR input of one of the QSC's channels, and then run a standard 1/4" cable from one channel's input to the other (OR use a 1/4" TRS cable and maintain balanced connections between everything) - I've done it myself and it works great!
Senior Member
Username: keith_h

Post Number: 1814
Registered: 2-2005
Posted on Wednesday, November 21, 2012 - 4:42 am:   Edit Post

Give me a call if you want to talk about setting this up. I use QSC PLX2 amps both bridged and unbridged and can go through the settings and connections. I can probably even make a trip down that way over the weekend.

Senior Member
Username: ajdover

Post Number: 1005
Registered: 11-2003
Posted on Friday, November 23, 2012 - 1:19 pm:   Edit Post

Many thanks to Keith, Will, David and Wolf for all the input and suggestions. I actually took Keith's and David's suggestions, and I'm now running my rig full range, using an XLR to XLR patch to "bridge" the inputs on my QSC, with a TRS going from the output on the F1-X full range to the input of Channel 1 of my amp. It works great! I'm also running my SF-2 in the effects loop of the F1-X in mono mode on the SF-2. Only thing left is to figure out how to connect my Korg DTR-1000 tuner, but that shouldn't be a big deal.

Thanks again, guys. You personify why I'm an Alembic player.

Senior Member
Username: ajdover

Post Number: 1006
Registered: 11-2003
Posted on Friday, November 23, 2012 - 1:21 pm:   Edit Post

Actually, that's a TR cable from the F1-X to the QSC.

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