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Why are all QSC PLX amps the same weight?

Discussion in 'Amps and Cabs [BG]' started by PlayTheBass, Apr 4, 2005.


  1. PlayTheBass

    PlayTheBass aka Mac Daddy

    Dec 7, 2004
    Carmichael, CA
    This may be a dumb question, but I couldn't find the answer anywhere so I thought I'd ask: why are all the amps in the PLX series the same weight (21 lbs)? (I don't know if other manufacturers have similar lines where the weight stays constant while power rating increases -- I'm just asking about QSC because I'm familiar with them. And because, well, Bob Lee's in the house! :))
     
  2. 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
    They're not exactly the same weight, but they're all over 20 pounds and less than 21.
     
  3. msquared

    msquared

    Sep 19, 2004
    Kansas City
    It's all so clear now!
     
  4. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    The power amp design of the lower power PLX is different than the higher power ones (not looking at the web sight, I believe the crossover point is between the PLX1602 and PLX2402).

    Besides...Bob Lee and crew are just clever folks!!!!
     
  5. Trevorus

    Trevorus

    Oct 18, 2002
    Urbana, IL
    It probably has a lot to do with the actual amplifying circuitry. The power source is probably largely the same in the amps, as far as power capabilities goes.
     
  6. PlayTheBass

    PlayTheBass aka Mac Daddy

    Dec 7, 2004
    Carmichael, CA
    Thanks, Bob. If it's not a proprietary issue, can you explain what's changing from model to model as the power rating increases?
     
  7. 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
    The components, the number of them, the way they're arranged, etc. Your best bet would be to download the schematics for each model and analyze the differences.
     
  8. PlayTheBass

    PlayTheBass aka Mac Daddy

    Dec 7, 2004
    Carmichael, CA
    Cool. I didn't know the schematics were online. Thanks!

    I was just always curious how the additional power was gained with (virtually) no weight gain, and what drove the cost increase (other than market value).

    Just as a joke to myself, I've always had this vision of some guy reaching into a 1202 and moving a jumper and saying, OK, another 3402 is good to go! :)
     
  9. Lowtonejoe

    Lowtonejoe Supporting Member

    Jul 3, 2004
    Richland, WA
    Moving a jumper...man, that would be way too cool! Heck, even two jumpers!!

    :)

    I also have wondered how they get more power without significant weight gain. Usually more power = more weight. Is this the magical 'switching' power supply doing it's job? So, do they all use the same output transformer? Do they use an output transformer? Lemme guess, we are now back to the power supply.

    :confused:

    Joe.</snip></snip></snip>
     
  10. alexclaber

    alexclaber Commercial User

    Jun 19, 2001
    Brighton, UK
    Director - Barefaced Ltd
    I think it's down to the switching power supply gaining very little weight as its capacity is increased. And the demand for more power from the wall doesn't increase linearly with the power output because the amp topology is different between the class AB lower models and the class H (I think) higher models, making the 2402, 3002 and 3402 more efficient.

    The other thing that should get bigger and heavier are the heatsinks, but the higher spec amps aren't capable of driving full power constantly into 4 ohms bridged without overheating. In reality that doesn't happen and the amps are comfortably capable of riding the limiters driving subs without any overheating issues.

    Alex
     
  11. 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
    All five PLX models use the same heat sinks.

    In amps with conventional power supplies, a more powerful model would generally need a bigger, heavier transformer than a lower-power one would. In the PLX amps, the power transformer is running at about 110 kHz, so it can be much smaller--it weighs only about a pound. Technically, we could make the transformer cores smaller for the PLX 1202 and other lower-power ones, but it costs a lot less to make them all with the same core at the expense of a few ounces of weight, so it's not worth it. The PLX 3402 has 16 output transistors (and support components) plus the class H rail-switching circuitry; the PLX 1202, at the other extreme, has 12 output transistors. Some of the power supply components in the PLX 3402 have higher voltage and current ratings than those in the PLX 3402.