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Need help with "How To" QSC preamp/amp connection

Discussion in 'Amps and Cabs [BG]' started by doc540, Jun 23, 2008.

  1. Jun 23, 2008 #1
    doc540

    doc540

    Jul 28, 2003
    Beaumont, Texas
    What's the best way to connect the single, mono phone output on my SansAmp Tech21 to 2, stereo inputs (phone or XLR) on a QSC PLX1804 power amp?

    Do I need to get a custom cable made or are they available over the counter?:confused:

    thnx
     
  2. Jun 23, 2008 #2
    BassmanPaul

    BassmanPaul Inactive

    Aug 25, 2007
    Scarborough Ontario Canada
    If you check your QSC manual you should see how to parallel the inputs (should be a switch for this). Then you connect the output from the SansAmp to the correct input of the amp (usually channel 1).
    Job done.

    Paul
     
  3. Jun 23, 2008 #3
    doc540

    doc540

    Jul 28, 2003
    Beaumont, Texas
    Thanks. My PLX1602 has that feature, but the more simple, 1804 doesn't. It's a straight, stereo hookup.

    I might be upgrading to the 1804.
     
  4. Jun 23, 2008 #4
    Bob Lee (QSC)

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

    Jul 3, 2001
    Chester, Connecticut
    Former Technical Communications Developer, QSC Audio
    You can use a Y cable.

    Or connect the preamp output to one channel's input. Use a second cable to connect the unused input jack on that channel to one of the input jacks on the othr channel.
     
  5. Jun 23, 2008 #5
    doc540

    doc540

    Jul 28, 2003
    Beaumont, Texas
    thnx...simple enough
     
  6. Jun 23, 2008 #6
    Crabby

    Crabby

    Dec 22, 2004
    I just received a PLX1804 in a trade and it came with a little XLR jumper cable so that a mono signal can be plugged into channel one then the jumper cable and be plugged from channel one into channel two and voila!

    best power amp I have ever used. I am running my Eden Navigator into it using the stereo channels and then out to a pair of 210 cabs. I have so jones about this rig as the whole rack weighs about 23 pounds and I'm getting 1200 watts in stereo with the two 8 ohm cabs.

    IMGP0564.gif

    IMGP0562.gif

    IMGP0565.gif
     
  7. Jun 30, 2008 #7
    doc540

    doc540

    Jul 28, 2003
    Beaumont, Texas
    Thanks for the pics. I have it installed and cranked up already.

    Bob Lee,
    Thanks for posting with help about my PLX cable setup.

    I have one more question:

    I just sold my PLX1602 and replaced it with an 1804. Apart from the obvious physical differences (LED's, switches, power, etc.) what, if anything, will be different in the sound reproduction qualities of the 1804 compared to my old 1602?

    The spec's listed on the QSC site show a few differences, but I don't know how to interpret them as they relate to sound quality.

    I'm using it to power a SansAmp Tech21 RBI bass preamp into two, 4 ohm, bass cabs.

    Thanks! I've been using QSC power for over 25 years.

    Rig2-1.jpg
     
  8. Jun 30, 2008 #8
    ulrich

    ulrich

    Aug 21, 2005
    Glendale, CA (LA County)
    I would get fussy, and use a balanced TRS, and, or XLR, cable. Though given that the signal is going right back in to the same amp, I suspect that a TS, jumper cable from your pedal board would be fine.

    What do you say Bob; is balanced that big a deal, in this case?
     
  9. Jun 30, 2008 #9
    Rick Auricchio

    Rick Auricchio Registered Bass Offender Supporting Member

    Nov 27, 2007
    Cambria, CA (Central Coast)
    Doc, if the preamp output is balanced, then you should use a TRS 3-conductor plug/cable to connect to the power amp.

    It will work fine with a standard 2-conductor cable (like an instrument cable), but you will lose 6dB of volume.

    That 6dB difference is like having 1/4 the power.
     
  10. Jun 30, 2008 #10
    doc540

    doc540

    Jul 28, 2003
    Beaumont, Texas
    Thanks, everyone. I got the cable connections situation handled. (I use the 1/4" phone output of the RBI split into two, 1/4" phone connections to each channel of the stereo amp. I used the XLR output to run directly into the sound system when necessary.)

    Now I'm asking Bob Lee about any audio differences between the 1602 and 1804.

    thnx again

    [​IMG]
     
  11. Jun 30, 2008 #11
    amos

    amos

    Oct 23, 2003
    SE Portland Oregon
    If using both sides of the amp, go for the 1804. I run out of headroom with my 1602, and I'm only running two 1x12s on one side and one 2x10 on the other. The 1602 seems to be a better amp for bridging (4-8ohm).

    As a side note, when I ran a 2.67 ohm load on one side of the 1602 it gave me a pretty big bump in volume, so that may be part of it (running dual mono @ 2 ohms a side w/ the 1602)
     
  12. Jul 1, 2008 #12
    Bob Lee (QSC)

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

    Jul 3, 2001
    Chester, Connecticut
    Former Technical Communications Developer, QSC Audio
    The PLX1804 is not designed for load impedances of less than 4 ohms per channel. If you try to drive, say, 2 ohms per channel, the amp may shut down, and if this happens the sound quality will suffer and be completely different from the PLX1602.
     
  13. Jul 1, 2008 #13
    Bob Lee (QSC)

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

    Jul 3, 2001
    Chester, Connecticut
    Former Technical Communications Developer, QSC Audio
    The amp's power capability will not change, though.
     
  14. Jul 1, 2008 #14
    Bob Lee (QSC)

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

    Jul 3, 2001
    Chester, Connecticut
    Former Technical Communications Developer, QSC Audio
    If the cables are short, a few feet or less, unbalanced probably would be fine.
     
  15. Jul 1, 2008 #15
    doc540

    doc540

    Jul 28, 2003
    Beaumont, Texas
    Thanks

    All things being equal prior to input, the 1804 into 4ohms will sound no different than the 1602 into 4ohms?

    Just wondering about the sound quality when connected properly to two 4ohm cabs in stereo mode?