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hookup question: power amp/preamp

Discussion in 'Amps and Cabs [BG]' started by grinx, Jul 31, 2003.


  1. grinx

    grinx

    Mar 24, 2003
    Raleighwood, NC
    hey all

    i have an alembic f1x preamp that has a full-range 1/4" out.

    i want to get a qsc plx 2402 http://www.qscaudio.com/images/hi_res/PLX3402_back_hi.jpg

    if i have one 1/4" out from my preamp, where do i plug it into the qsc power amp pictured above? thanks.

    i would assume EITHER 1/4" channel 1 or 2. then speakon from amp to speakon on my 2 cabs.

    thank you
     
  2. Mcrelly

    Mcrelly

    Jun 16, 2003
    Minnesota, USA
    sounds good to me.
     
  3. grinx

    grinx

    Mar 24, 2003
    Raleighwood, NC
    but if i don't plug anythign into channel 2 INPUT, will get anything out of channel 2 OUTPUT to one of my cabs?

    thanks
     
  4. David Wilson

    David Wilson Administrator Staff Member Administrator Supporting Member

    Oct 14, 2002
    Lower Westchester, NY
    if you're running the amp in stereo mode, you only get output out of the channels you are inputting to.

    If you're running in bridged mono mode, you'll get output of both channels from one input.

    As you have an Alembix F-1X, are you looking to split the frequencies and bi-amp? If so, you could use the x-over outs on the Alembic and use both QSC inputs to drive both outputs.
     
  5. Mcrelly

    Mcrelly

    Jun 16, 2003
    Minnesota, USA
    If you only have one preamp signal I assume you plug it into ch 1 1/4" and have the little switches set for "bridge" mode. you should have a 4 conductor cable with a 4 conductor "speakon" plug at one end and 2 conductor at speaker iend if you have ONE cab. The trick apparently after setting the little switches to "bridged" you have to be sure to wire the "speakon" connector to the +1 and +2 terminals on one end and the other end? +1,-1?????? not sure.

    OR

    USE A two conductor 12 to 18 AWG wire with two bare wires or bananna plugs at one end and mono-1/4" plug at the other.

    I tried searching "speakon wiring guide" and found some things, but not exactly your situation.
     
  6. grinx

    grinx

    Mar 24, 2003
    Raleighwood, NC
    i COULD go crossover. I plan to have an EA 12" cab and an EA 10" cab.

    figured it would jsut be easier to run full to them both.

    maybe not =p

    thanks for the ideas, gang. it looks easy to setup, i guess it isn't

    <=====needs a sound tech
     
  7. Mcrelly

    Mcrelly

    Jun 16, 2003
    Minnesota, USA
    o.k. I think I'm starting to get this. set the switches for parallel mode. that uses ch1 input fed through the TWO speakon outputs. wire the ch1 and ch2 ouputs to the 4 conductors in the speakon plugs as designated on the back of the amp, but at the speaker end I'm still not sure? send those wires to 1+ and 1- ???

    maybe send an email to QSC. I don't want to be responsible for blowing your amp or anything!! read the manual if you get one with the amp!
     
  8. David Wilson

    David Wilson Administrator Staff Member Administrator Supporting Member

    Oct 14, 2002
    Lower Westchester, NY
    it's actually not that hard. But I'm sure all the options available make it sound confusing!

    Check out the PLX series manual here.
    It describes how to do bridged mode.
     
  9. Mcrelly

    Mcrelly

    Jun 16, 2003
    Minnesota, USA
    that would be cool you could have one filter set to 50hz (EA 10) and the other at 30hz!

    here is a QSC connection manual for that series of amp check out PAGE 15 ONWARD A COUPLE.... http://www.qscaudio.com/pdfs/plxuser.pdf
     
  10. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    Set the inputs to parallel (switches 4, 5, and 6), and plug your pre output into either channel 1's or channel 2's input. Use channel 1 to run one cab and channel 2 for the other.
     
  11. grinx

    grinx

    Mar 24, 2003
    Raleighwood, NC
    *hug*

    thanks!
     
  12. Hey, Bob, I was also thinking about getting a PLX 2402. In stereo mode, would I be getting 1200w @ 2 ohms to each cab? Or would I just be getting 600w to each cab? And if wanted to use a 4 ohm and 8 ohm cab together, I would be using 2 ohms right?

    Thanks,

    Sean
     
  13. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    Hi Sean,

    If you put an 8-ohm cabinet on one channel, you'll have an 8-ohm load on that channel. If you put a 4-ohm cabinet on the other channel, it'll see a 4-ohm load.

    The amp is rated at 425 and 700 watts per channel into 8 and 4 ohms, respectively.
     
  14. Yeah, I kinda figured that afterwards. I got confused and thought that the load from both channels gets combined. Thanks for clearing that up for me!

    Sean

    P.S. How come none of the PLX series amps go down to 2 ohms bridged?
     
  15. hmjuice

    hmjuice

    May 20, 2000
    Austin, TX USA
    I have a 2402 and an EBS pre-amp. I run it in stereo with a cable from each output to each input. That powers an Acme Low B2 4ohm in one channel and 2 Aguilar D112 8ohms on the other channel (4ohms stereo). Although you could also use the parallel mode as well. I've never needed to bridge the amp for more power, I don't even move the volume more than 3/4 on the PLX. I did make my own speaker cables because I wanted speakon ends. I've had that amp for 3 years and never had a problem.
     
  16. Bob Lee (QSC)

    Bob Lee (QSC) In case you missed it, I work for QSC Audio! Gold Supporting Member Commercial User

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    The minimum load impedance on PLX amps (and most other good amps, too) is 2 ohms per channel. Running bridged mono into 4 ohms is electrically equivalent to 2 ohms per channel.

    If you want to run bridged into 2 ohms, you'll have to find an amp that's rated down to 1 ohm per channel. ;)