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QSC PLX 2402 users - Wiring question

Discussion in 'Amps and Cabs [BG]' started by jivetkr, Nov 18, 2003.


  1. jivetkr

    jivetkr

    May 15, 2002
    NJ
    I just got another cabinet & I ran into some issues with the wiring to the power amp. Both cabinets are 8 ohms & they have the same power rating.

    I was tring to run the amp in parallel mode, so I had my preamp going into channel 1, I had switches 4,5,&6 over to the right (on) & had the bridge mono switch set to the left (off). I connected one cabinet to channel 1 & the other to channel 2. The result was that only the cabinet connected to channel 1 was producing any sound. The front of the amp did indicate that I was in parallel mode.

    According to the manual, when connected in this manner each channel of the power amp will drive its own speaker load & I should only have to connect the preamp out to channel 1 of the power amp.

    The only way I could get it to work was to run in bridged mono mode taking channel 1 into one cabinet & then connect that to my second cabinet. That sounded awesome, with tons of power & barely pushed the power amp at all....Which I was happy with.

    I'm just confused...what I am doing wrong when wiring in parallel? Should I wire this in another way or did I have it right?

    Any help would be appreciated.
     
  2. Schwinn

    Schwinn

    Dec 4, 2002
    Sarasota, FL
    hmmm...that should have worked. This is a stupid question, but did you switch the cables around to see if that was it? Also, maybe a bad output jack? It looks like you had it set up right, but I could be wrong.

    By the way, is it new or used?
     
  3. jivetkr

    jivetkr

    May 15, 2002
    NJ
    I did try to switch the cables around.

    The amp is fairly new. I bought it about 1 year ago & its been babied the whole time.
     
  4. Schwinn

    Schwinn

    Dec 4, 2002
    Sarasota, FL
    Is this the first time you've tried to run in parallel then?

    Did you try running in stereo (if you have another preamp cable around)?
     
  5. jivetkr

    jivetkr

    May 15, 2002
    NJ
    I've done this before with fine results.

    I tried the stereo setup & that didnt work either.
     
  6. 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
    Were the signal level LEDs lighting up on channel 2?

    How did you have the outputs hooked up to the speakers? Did you succeed in swapping the speaker cables around?
     
  7. jivetkr

    jivetkr

    May 15, 2002
    NJ
    Bob....Yes, the led's were lighting up in channel 2. I just wasnt getting a signal through the speaker....wierd.

    As for the outputs, I had one speakon to speakon cable going from channel 1 to speaker A & I had a speakon to 1/4 inch cable going from channel 2 to cabinet B.

    I did try to swap the cables, taking the speakon to 1/4 inch cable to cabinet A from channel 1 with no problems.

    It sounds like the problem is isolated to the channel 2 connector. What do you think?

    Also...Is the way I ended up getting it to work ok? Or is there a possibility for damage to the amp?
     
  8. 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
    It sounds like perhaps the Speakon plug wasn't turned fully clockwise in channel 2's output jack. The two Speakon jacks are pretty close together, and close to the binding posts as well, so the second plug you attach to the amp can be a bit difficult to turn fully.

    Try very lightly spraying some silicone spray or WD-40 on the mating surfaces of the amp's Speakon jacks. Then hook up a cable to channel 2's output first, then the other cable to channel 1.

    See if that works.
     
  9. jivetkr

    jivetkr

    May 15, 2002
    NJ
    OK...I'll try that.

    If I am running the amp in parallel, but I do not have a speaker hooked up to the channel 1 output but I do have one hooked up to channel 2, should I be getting a signal on channel 2? I tried that as well with both cables & didnt get a signal on channel 2. Both volumes were up BTW...
     
  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
    Yes, you should.

    Do you have any way of using the binding posts? If there is signal at the binding posts, then there should also be signal at the Speakon output, since they're connected in parallel with each other.

    But first, check the wiring of the Speakon plug. Open it up and make sure the conductors are wired to 1+ and 1-.
     
  11. This is a wild stab perhaps, but did you check switch 7? If it is set to "bridge mode on" only the Channel A speakon will work. Nah, I'm sure you saw that part in the manual...
     
  12. 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
    No, there will still be Channel 2's signal on the lower Speakon in bridged mono.
     
  13. Thanks for the info Bob... that makes life much easier. I misunderstood the bridge mode wiring diagram on Page 11 (bottom left) that shows the 4 connector speakon and states "upper speakon only". Clearly then, only the upper speakon supports a 4 wire connection, but the bottom speakon is still active in bridge mode. Got it!

    Back to your regularly scheduled thread topic.