Class D poweramps?

Discussion in 'Amps and Cabs [BG]' started by Suburban, May 2, 2002.

  1. Suburban


    Jan 15, 2001
    lower mid Sweden
    Hi, guys and gals.
    Anybody know of any Class D, "switching" power amps out there?
    Meaning power only, I got a sweet preamp.

  2. Could you elaborate on why you prefer a class D amp?

    Most modern (last 3-4 years) PA amps are class D.
  3. bben


    Feb 28, 2002
    Santa Fe, NM
    Although they are not all called "class D", there are a bunch of power amps out there now with switching power supplies.

    A partial list includes the Acoustic Image Clarus series, Crown K series, Stewart World series, Walter Woods amps, Peavey DPC series, and QSC PowerLight and PLX series.

    I have a QSC PLX1602 and like it a lot, although you need a strong preamp to drive it (I use an Avalon U5).
  4. Suburban


    Jan 15, 2001
    lower mid Sweden
    I am under the impression that class D is in effect a "switching" amp....

    A I wrong again???? :oops: :confused:
  5. geshel


    Oct 2, 2001
    I thought Class D referred to the actual power amp section, not the power supply, being switching?

    I thought the only switching power amps out nowdays were the Clarus, the Peavey DPC, maybe a couple others?

    Lots with switching supplies though, yes.
  6. Christopher


    Apr 28, 2000
    New York, NY
    "Class" refers to the way in which the amp's output section handles the waveform, not the type of power supply. Conventional class A and AB amps are heavy, bulky and relatively inefficient in comparison with Class Ds.

    The Clarus is the smallest of them all, but it only puts out about 130W into 8 ohms. Since you already have a preamp, I'd check out the Stewarts or the Peavey DPC. The Crown K and QSC PLXs are powerful, but they take up two rack spaces.

    As for the Walter Woods, expect a two year wait unless you find one used.
  7. Phat Ham

    Phat Ham

    Feb 13, 2000
    The QSC PLX series amps are not class D amplifiers. The QSC PLX 1602 and below have traditional class AB output stages, while the PLX 2402 and higher have class H output stages.
  8. bben


    Feb 28, 2002
    Santa Fe, NM
    There's a lot of confusion about the terminology related to switch-mode power supplies, and I am not the right one to sort it out, maybe Bob Lee could help us.

    My understanding is that, whatever it is called, an amp that is switching the power supply 230,000 times a second is using the output transistors as switches rather than as analog current amplifiers. I believe this is true no matter what configuration the output transistors are in, or what form of code modulation is used.

    In the QSC example, from looking at the online schematics, the PLX1602 has the same audio circuitry as the RMX1450. The RMX1450 is a class AB amp, with a traditional DC power supply. I don't think the PLX1602 can be called a class AB amp, though. It doesn't operate the output circuitry the same way, it gets a little more power from the same circuits, and (most important) it has the principle benefit of all of these amps, light weight. The RMX1450 weighs 40lbs and the PLX only 21lbs.

    Class D output stages use simple Pulse Width Modulation and a fixed power supply voltage. The output devices are either ON or OFF, and they are switched very fast. The average value of these hi-frequency spikes of varying width is what the speaker sees, so it sees the original audio signal. It's all about the low-pass filter effect of real world devices.

    Class H uses a linear output stage, but the power supply voltage tracks the required output level, which improves efficiency by decreasing the wasted power in the output stage during low level signals.

    More details at the link above.

  10. fivestringdan

    fivestringdan Supporting Member

    Dec 4, 2001
    Little Rock, AR
    Don't forget Crest amps!!
  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
    No, the switching is in the power supply, not at the output transistors. The switching in the power supply is for the purpose of creating its own AC for the power transformer. A small, ultra-low-impedance power transformer operating at 115 kHz can outperform a huge, heavy transformer operating at 50 or 60 Hz.

    The output section of the PLX 1202 and the PLX 1602 are class AB, as are all of our non-H models. (Technically, it is class AB+B, in that the driver transistors operate in class AB, and they drive the power-handling transistors, which operate in class B.) The class H technology we use is merely an extension of class AB+B involving intermediate supply rail voltages to boost efficiency.
  12. bben


    Feb 28, 2002
    Santa Fe, NM
    Thanks, Bob.

    So we leave the QSC PLX amps off the list of class D, and I go off to poke around the web and become a bit better informed:

    The Peavey DPC uses the phase relationship between two non-changing pulses, instead of pulse modulation, but they still call it class D - see Bass Player's review of the DPC1400

    I'm not at all clear what Crown is up to with their K2 "BCA" circuitry, but underneath the marketing hype on their website it does look class D.

    Walter Wood's stuff I have no idea, no web site, almost has to be a switching amp with the high power levels and small sizes.

    The Stewart World series have switch mode power supplies and class H circuitry.

    The Crest LT series are class D.

    Which brings me back to the question, Suburban, why class D as the primary question rather than how an amp sounds and how much it weighs in relation to the power output?
  13. Suburban


    Jan 15, 2001
    lower mid Sweden
    Your question is justified, indeed.
    Why I ask for input of class D power amps, is because I want great, powerful sound out of "a stamp".
    Due to limited storage, I can only have one rig. That I have to haul between home, church, and all other (much) smaller or (slightly) larger places, to rehearse or gig. Thus, I need a low weight/minimal space amp, without a fan (disturbance in small rooms), so I can spend that volume and weight on the speaker cab.
    And, as far (short!:rolleyes: ) as I know, that equals class D.

    I am open to any correction. And to websites of Crest and other producers of amps as stated above.
  14. bben


    Feb 28, 2002
    Santa Fe, NM
    Well, Suburban, based on my (very) small fund of knowledge gained by poking around those websites the other day, I think one needs to look at overall weights, too. The Clarus and Peavey DPC are very light and Class D. The Stewart World amps are very light and not class D, and the QSC PLX series are quite light and not class D, either. The Crest LT series are class D, but not very light at 32 lbs. That's all. ;)
  15. what about class "H" ????
    what are the difference between class h and class d?
    which are better?
  16. Read my earlier post in this same thread.

  17. chucko58


    Jan 17, 2002
    Silicon Valley, CA, USA
    I paid for all my gear myself. Well, me and MasterCard.
    Then there's the Laney B-1 head, which is Class T (Tripath's patented/trademarked variation on Class D), but with a heavy conventional power supply.
  18. lneal


    Apr 12, 2002
    Lee County, Alabama
    Threads like this demonstrate the excellent job that manufacturers and marketing types have done in confusing non-technical people. As a graduated electronics tech-nut, all of that amp jargon makes sense to me. But to the majority of people it only serves to confuse. Maybe that's what the manufacturers want, I don't know. To their credit, QSC does the best job of explaining their technology and the reasons for it, IMO. However, explanations from them or anyone else cannot be properly and completely understood unless the explainee has technical training on the subject. Manufacturers know this and exploit it in their ads.

    Here's my advice to non-tech heads looking for an amp: buy the one that sounds best to you, and meets your other criteria! Don't matter what anyone else thinks as long as you dig it.