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Aguilar/QSC problem

Discussion in 'Amps and Cabs [BG]' started by neptune, Feb 27, 2001.


  1. neptune

    neptune

    Feb 2, 2001
    Maryland
    Hey Folks,
    I hope one of you more knowledgeable types can help me out. In my ongoing search for great tone I recently acquired a preamp/power amp setup for the first time, and I don't think it's running up to speed. Symtoms are: Lack of what should be substantial punch, and occasional distortion (not the good kind) The signal LED on the QSC might reach the -20 db LED at best and the clip light isn't even THINKING about coming on. Here's my signal chain:
    1. Stingray 5
    2. Aguilar DB 659 preamp
    3. 1/4" (tip/sleeve) from (unbalanced?) line out of the Aguilar to 1/4" tip/sleeve line in (balanced?)on the QSC PLX-2402.
    4. QSC is running in stereo, clip limiting engaged, low pass filter set to 50 hz. I'm using channel 1 (should be 750 watts at 4 ohms).
    5. Speakon NL4FC output from the QSC to Speakon input of an Epifani T-212 (600 watt cabinet, pulls 4 ohms). The Speakons have 4 visible contact points when looking directly into them, but I think it's a 2 conductor. I haven't figured out how to open them up to make sure yet...
    I really appreciate any help you can give me
     
  2. john turner

    john turner You don't want to do that. Trust me. Staff Member Administrator

    Mar 14, 2000
    atlanta ga
    nice rig you got there neptune.

    i know this might sound insulting - and i don't mean it that way, but when was the last time you checked/changed your battery?

    what you are describing sounds like a dying onboard battery - something you might want to check into if you haven't already.

    just a thought.
     
  3. neptune

    neptune

    Feb 2, 2001
    Maryland
    Thanks for the thought, but the battery's good to go. I feel like it may be something in my cable setup, not sure. I've seen some posts about unique cabling and QSC's, but I don't quite understand the balanced/unbalanced/speakon stuff. Thanks again.
     
  4. coyoteboy

    coyoteboy easy there, Ned Supporting Member

    Mar 29, 2000
    Sactomato, CA
    I might be wrong, but a low pass filter set to 50hz sounds wrong. Your cutting off frequencies abouve 50hz. Turn the filter off, you shouldn't need it for bass guitar, its for PA subs.

    Gotta love that 2x12...
     
  5. LowRanger

    LowRanger

    Dec 24, 2000
    I think the low pass filter is set OK, everything below 50Hz will be rolled off.

    I had something like this happen when I first connected an Alembic F1-x to my QSC. Turns out the problem was a bad crimp (it was pretty visible) right at the start of the input chain.

    If you have a DI out (or headphones out) on your pre, do the same symptoms appear there (without your power amp even connected to the pre)? If so, then either your bass or your pre has a problem, and your power amp is fine. If there is no problem at the DI/Headphone outs, then perhaps you are using a speaker cord for an interconnect between the pre and power amps? What about your speaker cord... try a new one?

    If you're using speakons, did you try channel 2 of the QSC to the cab? The first time I tried hooking up an Acme B2 to my QSC, I had a big problem... thought the amp had died. Seems, however, that it worked OK on channel 2. Turns out that Andy at Acme wires his speakons different from QSC, a rewire of the speakon cable connectors (both ends) solved that. My QSC PLX3002 has both channels 1 and 2 (bridged mono I believe?) in channel 1 speakon, so the problem was resolved by using only channel 2.

    Good luck, I know it's frustrating!
     
  6. neptune

    neptune

    Feb 2, 2001
    Maryland
    I'm using a 3" instrument cable between the Aguilar and the QSC so hopefully that's not the problem. That's a real good point about trying channel 2 on the QSC, LowRanger. There IS a difference between channel 1 and channel 2 on the QSC according to the manual, but I thought it was only in the bridged mode that it made a difference. I've also read that some posts about preamp output/power amp input voltage incompatability (primarily concerning Demeter's (which have some sort of internal variable control to match up the two). Jim Kinsey at Aguilar says it shouldn't matter in this case. I just need to get smarter on component setups. And Coyoteboy, you're right, You can't beat that 212!! Thanks again guys.
     
  7. LowRanger

    LowRanger

    Dec 24, 2000
    Depending on how your cab speakon is wired, it potentially COULD make a difference to the QSC, even if you don't select the bridged mono mode.

    The interconnect between the pre and the power amps may be good, but it may be bad, too, so it can't hurt to try a quick swap with another cable just to make sure. All it takes is one bad piece in the signal chain. My luck usually has it that it's the simplest piece in the chain that takes the dive... the one piece I thought would NEVER be the problem!

    Good luck, let us all know what you find!
     
  8. This isn't going to be a big help. But, when I had the Aguilar 659 with my CrownMT-1200 I had to switch to voltage switch inside the Crown. SOme pre run at the.77V some 1.4V, some you need the 26db setting. That is of course the QSC has those 3 options
     
  9. coyoteboy

    coyoteboy easy there, Ned Supporting Member

    Mar 29, 2000
    Sactomato, CA
    Not to be difficult, but I'll reiterate that a low pass filter attenuates frequencies above the set frequency, while a high pass filter rolls off frequencies below the set frequency. I can't see how a low pass set at 50hz would work very well for bass guitar. You should shut off the low pass filter on the power amp. Happy bassin'
     
  10. 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
    I'm with coyoteboy on this. Try it, for Pete's sake.
     
  11. LowRanger

    LowRanger

    Dec 24, 2000
    Coyoteboy, you're not being difficult :D:. Actually, we're both right :eek:.

    The term "low pass filter" is as you describe it, but the amp in question doesn't have one! Per the manual, it has a "low frequency input filter," and NOT a low-pass filter. They are two different functions. Again, per the manual, "the LF filter rolls off signals BELOW either 30Hz or 50Hz." The manual goes on to recommend a 50Hz setting for full-range cabs, and a 30Hz setting for subs; a 5Hz rolloff is engaged when the filter is disengaged to protect against DC.

    So the laws of filter design haven't been rewritten, but Neptune's wording is imprecise.

    And I agree; try it all. Another poster mentioned a potential pre-out power amp-in mismatch, a possibility; I had a Warwick Quadruplet that, maxxed out, couldn't get my QSC to move air at all, even with the Warwick's level out switch adjusted. My other pres have no problems.

    In a situation like Neptune's, I'd try anything and everything in a logical sequence... and pray!
     
  12. neptune

    neptune

    Feb 2, 2001
    Maryland
    You guys are an absolutely awesome resource!!! Sorry I haven't been able to get back to you sooner.
    I tried LowRanger's suggestion of Channel 2 on the QSC. That fattened up the sound noticeably. Another link in the chain: John Turner wasn't too far off with the low battery suggestion. I think I have a suspect Stingray pick-up. I hadn't noticed it distorting in my old rig, but I tried my old Jazz into this setup and it SINGS. I still may have preamp out/poweramp in mismatch. If I understand it correctly, The Aguilar puts out .77 volts. , the QSC input runs at 1.3 (?) volts at 4 ohms. Still foggy on that one.....
    Coyoteboy, Sincere apologies for the bad terminology concerning the "low frequency input filter." I'm still trying to learn this tech stuff..... I have to admit, sometimes I yearn for my old, high maintenance SVT......
    Really appreciate your help!
     
  13. Rockinjc

    Rockinjc

    Dec 17, 1999
    Michigan
    Does the Aguilar have XLR type ballenced output connectors? I have never used the 1/4" for ballenced TRS input but. Unballenced 1/4 always ended up less loud for me on my QSC/PLX 1602

    good luck
     
  14. neptune

    neptune

    Feb 2, 2001
    Maryland
    The Aguilar has two unbalanced 1/4" outputs and one balanced XLR type. The QSC has both 1/4" and XLR inputs (balanced). I may be better of getting a 1/4" to XLR type cable, not sure. I think the QSC wants to use a 1/4" TRS (tip/ring/sleeve) jack, but the Aguilar will only support a 1/4" TS (tip/sleeve) jack. Perplexing stuff for an old "Plug in and Go" type.....I still feel this setup's not stroking on all cylinders yet.
     
  15. Rockinjc

    Rockinjc

    Dec 17, 1999
    Michigan
    neptuna,

    Read me now and thank me later go XLR to XLR. Set your roll off filter down to 30 hertz if you play all five strings. It says right on the back of your qsc what pins to use I think its 1+ and 1- for normal and 1+, 2+ for bridge mono mode. If you had the wrong pins at the cabinet no sound would come out at all. As always, RTFM - http://www.qscaudio.com/pdfs/plxuser.pdf

    With such a powerful amp, you probably shouldn't run bridge mode. Though I have tried it with my 1602 and a single acme b2 without blowing things... be careful. Start with parallel mode and an XLR cable from preamp to the amp before you go hog wild. I think you will be happy using only one side of your amp for now.

    As far as an XLR cable, a short one should be best, but you could borrow a XLR type mike cable just to try it. :)

    jc
     
  16. neptune

    neptune

    Feb 2, 2001
    Maryland
    The Aguilar has two unbalanced 1/4" outputs and one balanced XLR type. The QSC has both 1/4" and XLR inputs (balanced). I may be better of getting a 1/4" to XLR type cable, not sure. I think the QSC wants to use a 1/4" TRS (tip/ring/sleeve) jack, but the Aguilar will only support a 1/4" TS (tip/sleeve) jack. Perplexing stuff for an old "Plug in and Go" type.....I still feel this setup's not stroking on all cylinders yet.
     
  17. Rockinjc

    Rockinjc

    Dec 17, 1999
    Michigan
    Just send the preamp to me, and I will check it out for you. :)

    j
     
  18. Bob C

    Bob C

    Mar 26, 2000
    Duluth, MN
    I don't own an Aguilar, but doesn't the web site info state the the XLR is for the DI, and the 1/4" goes to the power amp? I don't know that it will work the other way around, will it?

    On a related note, I have a new QSC PLX 3002 which I've only used a few times. It doesn't sound nearly as loud as I think it should. Without the usual long discussion of power ratings being misleading, let me just say I've used it with a Groove Tubes preamp (which I hate) and it doesn't sound any louder than my 350 watt Hartke head. I also briefly A/B'd it against a Crest CA9 on our PA subs, and the Crest blew it away.

    There are a few variables here which I will go into if anyone's interested. For now, I'm just wondering if anyone else has thoughts on QSC's perceived volume.

    Bob
     
  19. Two things
    THe XLR is only on the AGuilar as the DI out.

    Bob C, you mentioned about the Crest CA9, I have one on the way to put with my Aguilar 359. Tell me what you think about it. whats good bad etc.
     
  20. Rockinjc

    Rockinjc

    Dec 17, 1999
    Michigan
    Bob,

    How loud do you need to be? I own Acme, perhaps the most inefficent speakers you can buy, and I can get my metal fan drummer to ask me to turn it down, with half as many watts as you. ???

    For the DI, unless you are running stereo, you can come out the second channel of your amp for the di to the pa. I have a hard time understanding why it would not be worth trying. A spare cable is a tiny fraction of what the rest of the gear costs.

    The another issue I can think of is if the house circuit did not have enough current for the amp, but the simptoms would more likely be a short sag after playing a flurry of juice soaking notes. Though this never happend to me and I have played some real dives.

    jc