Best QSC Power Amp for 2 Ohm Loads

Discussion in 'Amps and Cabs [BG]' started by bgavin, Apr 21, 2003.

  1. Is the QSC 1850HD the best suited QSC amp for running stereo/parallel mono with 2 ohm loads?

    I'm hunting for a subwoofer power amp that can produce up to 900 watts per channel into 2 ohms, and run that way all day without damage or over heating.

    My PLX amps show a higher wattage output at 2 ohms, but I'm very concerned about stressing them this hard. I think the 1850HD is more tailored to 2 ohm loads...

    Bob Lee, or anybody?
  2. Eric Moesle

    Eric Moesle Supporting Member

    Sep 21, 2001
    Columbus OH
    I've been running one channel of my QSC PLX 3002 into 2 ohms, driving it quite hard, and it hasn't given me a stitch of problems. Doesn't even get the amp hot.
  3. My requirement will be tickling regularly the clipping LED. The operating environment is 100+ degrees ambient in the Sacramento summer.
  4. rok51


    Sep 2, 2002
    Crawfordville, FL
    From my digging around, QSC pretty much states that the PLX series has no problem with 2 ohms stereo/4 ohms bridged from now until the cows come home. When you move down to the RMX series, the 1850HD is the one to go to for extended loads of 2 ohm stereo/4 ohm bridged. Not that the other RMX units wouldn't operate at those loads...and would probably be just fine running a bass rig...I wouldn't want to use them for powering a dedicated subwoofer system with a lot of continuous low frequency content.

  5. Phat Ham

    Phat Ham

    Feb 13, 2000
  6. Yeah, I know.


    But.. that thread was concerned about cooling in a hot environment. This thread is concerned with balls-to-the-wall operation specifically at 2 ohms.

    I'm thinking about wiring my 2nd pair of 1x15 subs at 2 ohms each (instead of 8 ohms), and driving them with a 2nd power amp. This will let me add them to my PA setup, or use them with the bass rig when I need all four running.
  7. lo-freq

    lo-freq aka UFO

    Jan 19, 2003
    The Republic of Texas
    I believe what you are looking for is here (about 7/8 of the way to the bottom of the page--or search for "2-ohm performance").

    It does look like either the RMX 1850HD or RMX 4050HD would be the most stable into 2 ohm for the amount of power (or more) that you are looking for.
  8. I've seen that 1..10 rating message before. What it tells me is "thermal" stability.

    What I have not yet gotten answered is the question "which amp is least stressed at 2 ohms". I'm trying to understand if one model is better suited for the extended high current draw that occurs with a 2 ohm load. I don't want the hassle of an amp going into the shop due to premature failure from operating at 2 ohms.

    The 4050HD is not up for consideration at all, due to its weight.

    I got this from the QSC board:

    What I understand from the above is, the 1850HD still has plenty of output transistors to distribute the current load. I have a followup question posted, about comparing these features with those of the PLX 1602, which closely matches the output into 2 ohms. I suspect the 1850HD is better suited for hard usage at 2 ohms, than is the PLX 1602.
  9. rok51


    Sep 2, 2002
    Crawfordville, FL
    Why don't you specifically ask QSC that question? I'd like to know, as well.

  10. I already have.

    The DC resistance is 1.8 ohms.

    I have not yet run an impedance plot across the usable spectrum. The system impedance will be lowest at the tuning frequency of the vented cabinet (Fb) which is 20 Hz. Fb is below the lowest operating frequency of 30 Hz, plus I will probably have the 30 Hz filter enabled on the QSC.

    I expect the impedance to be 2 ohms or higher in the operating range. The vented cabinet will have the upper impedance peak of approximately 15 ohms near 35 Hz that declines toward the upper limit of 100 Hz. I expect very little inductive increase of impedance because of the restricted upper range.

    Link to Impedance Plot