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Please help me troubleshoot my new amp!

Discussion in 'Amps and Cabs [BG]' started by wiggleworm, Jun 19, 2003.

  1. wiggleworm


    May 29, 2003
    Hello, I hope I'm not asking stupid questions, but this is my first component system after many years of using combos. I have a brand-new preamp/poweramp/cabinet system that I tried for the first time last night. Sadly, the volume was significantly less than I expected, and when I turned it up, the clip light on the power amp came on and produced some awful crackling and popping noises. Let me tell you more about my signal chain:

    warmoth parts bass with passive lane poor pickup
    raven labs pha-1 preamp line out 1/4"
    qsc rmx850 power amp, 1/4" input #1 (rated 400w @4ohm per side, 830w@4ohm bridged)
    speakon->1/4 adaptor in output #1
    1/4"->1/4" speaker cable
    avatar B15H cabinet (4 ohms, rated 600w max)

    I tried different settings of the little dip switches on the back of the amp. The clip limiter made the clip sound less obnoxious but did not prevent it from happening. The low frequency filter didn't make much difference at either 30 or 50hz. Bridge mono mode, surprisingly, didn't make it any louder.

    I had to turn the volume control to maximum on both the preamp and the power amp to be heard with my band. The sound was excellent except for the crackling. Suspecting the raven labs wasn't providing a hot enough signal to the power amp, I tried using my Acoustic Image contra as a preamp, connecting the effects send to the power amp. The signal was even weaker. I even tried daisy chaining both preamps but I still couldn't get enough volume. Using a limiter/compressor reduced clipping a bit but I didn't like the sound as much.

    Maybe I'm crazy here, but it seems like 830 watts should be more than enough for this application, and even using 400w of one channel should be enough. After all, the cabinet is very efficient and is rated 600w max, and Dave at Avatar recommended using a 200-300w amp. But the speaker is barely moving! I can hear myself over a keyboard and percussionist at moderate level in rehearsal, but during louder passages I'm totally drowned out! Except for the distortion, which comes through loud and clear and causes the singer to turn around and glare at me.

    Any suggestions here? My 2 leading theories here are 1. I'm not connecting the speaker cable correctly to take advantage of the bridged mode (the QSC manual says that bridge mode uses different pins of the speakon connector, I'm not quite sure how to change that!) or 2. I need a different preamp that can provide a stronger signal to the amp (however, I researched this exact topic using the search feature, and many people are successfully using the PHA1 as a preamp). Any help would be much appreciated!

  2. wiggleworm


    May 29, 2003
    okay, so I'm going to try using banana plugs with the "bridge mono" output... any other suggestions out there?
  3. 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
    If you don't have the Speakon connected correctly, the amp will not perform as it is supposed to. Do not use it this way.

    Open up the Speakon connector and connect the wires as shown in the RMX manual. For bridged mono operation, use pins 1+ and 2+. See http://www.neutrik.com/images/ock/downloads/Media_293225003.pdf for details on how to do it. The connector used on cable ends is most often an NL4FC.
  4. wiggleworm


    May 29, 2003
    Thanks Bob, that's an amazing diagram! I have a small adaptor that converts the Speakon to a 1/4". I'll open it up and see what's in there. Or maybe I'll just go the banana route :)

    A little off topic, but can anyone educate me on the pros and cons of different speaker connections: 1/4", speakon, banana... my QSC even looks like I can attach naked speaker wire ?

  5. 1/4" phone plugs and jacks are the most common and have the least contact area, therefore some guys frown on them for connections using high power. I've been using them for years cause I'm old and that's what most of my stuff has. A Banana connector has a much larger contact area and is better for high power application. You can stack banana connectors in a single set of binding posts making wiring of multiple speakers easy. They do, however, come unplugged easily. Speakon are the most expensive and are the most versatile. They have a large contact area like a banana and lock into the jack and won't accidentally come unplugged. They also allow for multiple speaker cables to share the same connector. You can power 2 different speakers stereo or bi-amp with a single speakon. Neato:D