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Power Amplifier - RMX / PLX / Behringer

Discussion in 'Amps and Cabs [BG]' started by mlowe, Apr 16, 2005.

  1. Here's how new and innovative these amps really are. Not to label them all the same but they are somewhat nothing new.

    "Audio Engineering Society - Chicago Section - Meeting Review ...
    ... several observations he has made concerning amplifier design over the years.
    ... of the first class-D amplifier in 1958 and the first class-H in 1967"

    These designs are class H. Basically ab amp with a modulated power supply fed by the input. Not exactly rocket science.

    These big debates about design theft is really splitting hairs. There is also yet another design in Europe that is a mirror of the RMX 2450 spec and it's not Behringer.

    As the specs are identical in almost all aspects I'm starting to wonder if part of the designs are derived from the power stage semiconductor manufacturers and therfore follow an almost cookie cutter output.

    The real "design" part on QSC's behalf is the quality about the way they build in and use supportive circuits such as output short protection etc. maybe.....

    This design does apear to be somewhat "common".

    Take a look for yourself and compare to the RMX or EP Behringer.

    I'd be interested to know if the power transistors QSC are using in the output stage just happen to be Fairchild & Toshiba. The same power stage Behringer are using.
    I wonder if Fairchild or Toshiba provide suggested schematics for class H operation of power audio amplifiers for these semiconductor products. Of course the application of this suggestive circuit may provide similar power output specs but depending on construction, parts and implementation could give very different qualities.

    It's common practice amongst computer manufacturing to do this.

  2. Joe Beets

    Joe Beets Guest

    Nov 21, 2004
    Forget all the specs and data sheets. Go with the PLX. The biggest one you can afford. ;) ;) ;)

  3. Yep, I already there. The PLX after a lot of reading is very kick butt. Not only is it efficient, monster power, light, even the noise floor and distortion figures are way better than we'd ever need for bass.

    All I need to do now is find someone who will sell international instead of paying over 3 grand here for the PLX.
  4. popinfresh


    Dec 23, 2004
    Melbourne, Aus
    Don't forget changing the transformer etc and all the taxes of importing. Plus the fact that no-one will touch it if it's been changed.. Not sure how much it would be for a poweramp, but in your standard amp (Was looking at a Mesa Basis 2000) your looking at 6 or 700 for the transformer plus 200 in labour. Your looking at well over $1000 when all the taxes, GST and duties come in. Plus the initial shipping and price of the thing... it may not be worth it.
  5. It wouldn't be a problem as you can order it in 240V for here. They already build them for the export 240v market. So the cost will be US$995 + US$180 (frieght) = US$1175 > AU$1469 + import duty = $1542 x GST = AU$1696inc!

    Here is costs $3300. Not very funny.

    If the distributors were not so greedy I would rather buy it here but there is just too much difference. 30% margin is one thing but 200% is another. Especialy moving a box that is known for its reliability.

    Not bad considering an RMX2450 here from the distributor is $2150AU.

    That price is the monster PLX3402.

    I've built a few power amps so the tech part is ok. But even then for $1700 I wouldn't be bothered etching boards or picking up an iron. Especially as these PLX amps have extremley good performance. The power, damping factor, noise floor and THD are incredible. If anything it's well beyond required spec for a bass amp. For $1700 why not.
    It seems the QSC guys have also completly covered all the usefull features and logic to the usage of the amp. Modes, status, config options & protection etc.

    Anything on top would almost be gimick.

    I'm converted. Just have to find the site that sells them in the US for 995. I didn't bookmark it. Damm. :)
  6. Bob Lee (QSC)

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

    Jul 3, 2001
    Costa Mesa, Calif.
    Technical Communications Developer, QSC Audio
    Toshiba does not provide power amp schematics, at least not to QSC.

    The "class H" design you mentioned might've been actually what we term "class G." There seems to be confusion over which is which. Crown's major innovation in 1967 was the class AB/B DC 300. Hitachi pioneered class G production amplifiers in 1977 with their Dynaharmony series. However, a textbook published in 1964 by John Wiley laid out the concepts for a "quasilinear" class G (which is called class H in the UK and Japan, anyway) amp. Class G, in this sense, comprises tiered banks of transistors; the lower tier handles from 0 up to the lower rail voltage, and the upper tier handles from the lower rail up to the upper rail voltage.

    QSC innovations continued in the RMX series include grounded collector output transistors and the "Output averaging" short circuit current limiting. QSC also developed what are believed to be the first production class H (unlike class G, this uses the same output transistors for both low and high rails, and uses transistors to switch between the rails) amps in the early 1980s.

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