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PLX2 1804 running ONE cab, clipping problems

Discussion in 'Amps and Cabs [BG]' started by teedub, May 6, 2006.


  1. Hey all,
    Sometimes I've had to run EITHER my 210 or 212 (depending on the gig or rehearsal) with my PLX2 1804 , but have found that I have to run the amps parallel (daisy-chained via XLR) regardless of whether I've got one or two cabs connected to the outputs. If I disconnect the XLR jumper, connect the cab to the CH.1 output, and the pre in to the CH.1 input, I get clipping at basically any gain level. This is with the CH.2 gain at minimum and having nothing connected to it. However, if I connect the XLR from CH.1 to CH.2, set BOTH gain levels equal, even though I've only got ONE cab connected (via CH.1 output), everything's OK. Am I damaging my power amp by running the CH.2 gain without having a cab connected to it? Also, adjusting the CH.2 gain affects the volume of the output to the cab connected to the CH.1 output? How is this possible? :help:

    Thanks in advance!
     
  2. Lots of viewings, but no one knows?:meh:

    Just a little bump for some help.:smug:
     
  3. If your getting clipping at any setting, it sounds like the maybe your peramp level is too high. Maybe having the second channel connected is dropping the level on channel 1 just enough.
    Have you tested just running in channel 2 to see if you get the same thing?
     
  4. Munjibunga

    Munjibunga Total Hyper-Elite Member Gold Supporting Member

    May 6, 2000
    San Diego (when not at Groom Lake)
    Independent Contractor to Bass San Diego
    Run your preamp into Channel 1, play through it, adjusting the gain of the preamp upward until the PLX just starts to clip, the back it off a skosh. Then turn up the input attenuator (volume knob) on the PLX to the desired volume.
     
  5. No matter what level I set on the pre, the power amp still clips unless both gains on the power amp are set equally. I had another rehearsal today and can't figure it out. I'll try using the CH.2 output and see if it does the same thing.
     
  6. Lowtonejoe

    Lowtonejoe Supporting Member

    Jul 3, 2004
    Pasco, WA
    Weird.

    1. Is your XLR jumper wired correctly?

    2. You're not attempting to bridge the outputs, correct? (The 1804 won't bridge)

    3. You're not dropping below 4 ohms on either output are you? (The 1804 only goes down to 4 ohms per channel)

    4. Have you tried jumpering the channels using a 1/4" cable like in the manual? (I have no idea if it makes a difference)

    Or,

    Have you figured it out yet and do you know what the problem is?

    Inquiring minds want to know.

    :D

    Joe.
     
  7. It's wired as "balanced", but that shouldn't make a difference since the clipping occurs when I remove the XLR. Ultimately, I shouldn't have to use it for this application, since I only need one amp to power one cab. When I use both cabs, everything's great.
    I guess you answered your own question there.;)
    No, my cabs are each 4 ohms.
    It shouldn't make a difference (I assume they're parallel outputs), but I can't test that one because I don't have a 1/4" to XLR. I guess I could go XLR to XLR from pre to power. However, as mentioned above, the problem is that I want to run one cab with one amp.
    It works great with both cabs, and it actually works with one, but I have to boost the CH.2 gain, even though there's no cab connected to the CH.2 output. I just want to make sure I'm not hurting the amp by having the gain boosted on a channel without a cab connected.
    I'm hoping that Bob Lee will see this thread and save the day!:D Thanks for the reply, I hope I can get an answer soon! I'd hate to have to bring BOTH cabs to a little rehearsal..............well, I wouldn't hate it, but the term "overkill" may be used once or twice in my direction. ;)
     
  8. I think this will work, I'm going to test it now. CH.1 output is wired to be able to run 2 cabs if needed (+1 -1 +2 -2), and the CH.2 output is wired for just one (+1 -1). I think that may be where my problems lie.

    EDIT: Bullseye! I probably should have tried this first, but I guess lazyness got the best of me for a moment. My gear was still packed up for another rehearal tomorrow, so I was just going to test it then, but then the light bulb went on and I HAD to find out.

    Thanks to all!
     
  9. You should still be able to run channel one completely independant of channel two. Maybe one of your speakon cables has funky wiring...
     
  10. Lowtonejoe

    Lowtonejoe Supporting Member

    Jul 3, 2004
    Pasco, WA
    Yeah,

    that makes sense.

    :D

    Joe.
     
  11. They're both +1 -1, but thanks for the thought! :smug:. Though that would explain why the CH.2 gain has an effect.
     
  12. Flanker

    Flanker

    Feb 12, 2002
    UK
    I've been following threads about this amp with interest as I can't decide between this, a QSC3102 or a Powersoft equivalent.

    My priorities are Size/weight and Quality with price behind these.

    Is the 30Hz filter really a potential problem or just a nice feature?

    Would you buy this amp again given the choice?

    Anyone else with advice?
     
  13. Bob Lee (QSC)

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

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    Was the Speakon on the speaker cable miswired?
     
  14. Hmmm.... A few questions for you, first. :) How many cabs are you running, and what are their impedance and power ratings? Will you ever forsee the need to run your amp bridged?

    I'll give you a few reasons why I chose this amp over many other options. I wanted an amp that was VERY lightweight and powerful enough to cleanly run my two 4 ohm, 600W cabs, and wasn't going to break the bank. I didn't need the amp to be bridgeable, and I don't see myself adding more cabs in the future (never say never ;)). From what I read on these boards, I had it down to a PLX1602 I found on eBay at a great price. Got scammed, but got most of my money back. By now, the PLX2 line had come out, and at 13lbs, only 10" deep, and capable of pumping out 900W a side, the 1804 seemed too good to be true! I got a SUPER price from Lord Valve in Denver, and we had the deal sealed within a day. More info than you needed, but that's the Reader's Digest version.

    If your priorities are a lightweight/relatively inexpensive/high quality product, then QSC is the way to go. If you need bridgeable capabilites, maybe the 3102 is more for you. Powersoft is REALLY pricey in comparison, but I know at least one TB member has one. Check this thread for more info.

    Not a "problem" per se, more of a precaution. Trying to squeeze every little bit of power from your amp becomes tougher if it's reproducing subsonic frequencies, and I guess could potentially do damage to your speakers. I'm also just a little bit of a gear freak. :) I'm currently waiting on REMO's review........;)

    No question. But I've only had it for a few weeks. Gigging and rehearsing regularly, but there's many months/years of thumpin' ahead of it.........

    I'll fully trust QSC products until they prove me otherwise.

    I don't believe so. Ok, well I'm certain it's wired correctly, but I have no idea why it would transmit signal from CH.2. I'll take the cables into an "expert" shortly. :)
     
  15. Bob Lee (QSC)

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

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    You can just open up the Speakon plug and take a look.

    I've seen some Speakons where 1+ and 2+ were connected together, as were 1- and 2-. That could cause the problem you describe.
     
  16. Lowtonejoe

    Lowtonejoe Supporting Member

    Jul 3, 2004
    Pasco, WA
    EH??

    Why on earth would anyone want to do that?

    I'm not doubting you Bob. It's that I believe you that I find this so incredible.

    Would there be any theoretical advantage to wiring up speakons like that?

    :D

    Joe.
     
  17. Bob Lee (QSC)

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

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    I suppose it might've been meant to cover all the bases if you had speakers wired to 1+ and 1-, and some wired to 2+ and 2- (some are; I don't know why). I don't know of any advantage, other than that. These were on a couple of commercially made cables; I assume they were just as they came from the store, because the guy who owned them wouldn't even have attempted that (and probably didn't know that Speakons can be wired different ways). It was one of the most puzzling tech support calls I've ever had. To me, arbitrary non-standard wiring like that is really annoying.
     
  18. Lowtonejoe

    Lowtonejoe Supporting Member

    Jul 3, 2004
    Pasco, WA
    Ugh.

    Yeah, I can see how that would be annoying!

    :D

    Joe.
     
  19. Don't mean to sound like a complete dumb-ass, but I can't seem to get this thing apart..............

    I tried twisting it apart, but it doesn't want to go. The clip is in the way. They're Neutrik ends.

    FTR, when I had them made, I asked for +1 -1. I guess we'll see.
     
  20. Flanker

    Flanker

    Feb 12, 2002
    UK
    teedub

    Thanks a lot for the reply, I'm inclined to buy one of these mainly because they are so portable.Also buying QSC would be the well trodden path in terms of reliability/backup etc.

    It's handy to say the least having Bob here helping everyone out too. :)

    I have two Epi cabs, a 310UL and a 410UL(8 ohm). I don't need to bridge but it's always nice to have the option.I have a Epi Quest preamp and a EBS classic pre, both superb!

    If 600w into one side and say750w into the other isn't enough then nothing will be!!! Thanks again.
     

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