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switching power supplies in amplifiers?

Discussion in 'Electronic Design' started by [email protected], Apr 26, 2006.

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  1. Guest

    Hi all,

    Are home audio amplifiers typically powered nowadays with switching
    power supplies, or do they still have a massive 60hz power transformer
    inside?

    I went to Best Buy yesterday, and was surprised at how heavy many of
    the home audio amplifiers were...
     
  2. Joerg

    Joerg Guest

    Most that I have seen are transformer powered. Not that it couldn't be
    done with switchers but if the transformer solution is only one cent
    cheaper that's how it'll be done.

    Regards, Joerg
     
  3. Luhan

    Luhan Guest

    Well, I can tell you there are no longer any heavy transformers driving
    the speakers, not unless you are shopping for tube amps.

    Luhan Monat (luhanxmonat-at-yahoo^dot^com)
    http://members.cox.net/berniekm/
    "Reality: what a concept!"
     
  4. Guest


    So those 600W stereo amplifiers, are, um, 80% transformer, then? ;)

    If it's only a few cents cheaper, but 20% lighter, they could save a
    bundle in the shipping costs alone... ;)
     
  5. Guest


    Ah, I guess that's what I meant to ask. So, how are the speakers
    driven nowadays? Are they step-down DC-DC converters? (DC coming from
    a filtered bridge rectifier, connected to the mains?)
     
  6. Joerg

    Joerg Guest

    Many mfgs are pretty "creative" when it comes to power data. I have seen
    200W amps that had a transformer no larger than that in grandpa's tube
    set, 50-70W.

    With the rising oil prices that might play an increasing role. It's also
    size. Nowadays the macho thing isn't all the rage anymore. We bought a
    new set and my wife made it very clear that it should not be as large as
    the old Kenwood stack. It's amazing, the new stereo is barely larger
    than a shoebox but with the speakers that came with it the thing sounds
    almost as good as the old one. Plus it was a whole lot cheaper than the
    old one had been.

    Regards, Joerg
     
  7. Pooh Bear

    Pooh Bear Guest

    The transformer in a 600W amp is 'quite' heavy but probably not *80%* of the
    weight.

    SMPS PSUs are used in some amplifiers these days.

    Graham
     
  8. Tim Williams

    Tim Williams Guest

    Well, you can reduce line voltage to something more reasonable (depending on
    your power spec) with an iron transformer or a switcher, and you can drive
    the speaker through a linear amplifier similar to say, this:
    http://webpages.charter.net/dawill/Images/Fast Power Amplifier.gif
    This circuit can be class A, B or C. The only difference is the power
    dissipated at idle (heatsinks, eh?), and a small "tit" of crossover
    distortion in class C. Just add a small filter choke on the output to clean
    that up. Efficiency runs from maybe 45% class A (sine wave output) to oh,
    75% I think.

    Or, you can use a reasonably fast PWM circuit and drive the speaker that
    way. Class D with stiff MOSFETs nets you 90-99% efficiency. Linearity is
    questionable; with a fast, stable circuit you can at least wrap it with
    feedback and correct it back more or less.

    Tim
     
  9. Pooh Bear

    Pooh Bear Guest

    I wouldn't recommend Class C !

    Modern Class D can be very good indeed btw. 0.01% THD is quite acheivable from
    better examples now.

    Graham
     
  10. Tim Williams

    Tim Williams Guest

    Whyso? Bipolar transistors turn on pretty quickly, you can bias it within
    say -0.3V. A fast op-amp front end can correct that in a hundred
    nanoseconds. After the transient, one transistor is conducting and it's
    linear as any other amp is, with 60dBV NFB.

    Tim
     
  11. Pooh Bear

    Pooh Bear Guest

    Distortion at the zero crossing point is highly unpleasant. I'll defy you to
    find an output stage that responds adequately in a hundred nanoseconds too.

    I have *never* seen a commercial Class C amp for audio.

    Graham
     
  12. Tim Williams

    Tim Williams Guest

    Strange. I know a fellow who built his own 1kW amp and he says it's a few
    bits of a volt (just as I described) into class C. He says it's good at
    full power out to something like 300kHz, so damned if it isn't fast enough.

    OBTW, any regular output stage using reasonable transistors (fT > 20MHz or
    so, not wimpy-ass 2955/3055 or TIPxx stuff) will certainly respond in 100ns.
    I'd be more concerned about the diff amp responding in under 300ns... which
    can certainly be done, especially with somewhat faster transistors than
    generic (maybe 200-500MHz fT) and careful design.

    Tim
     
  13. Luhan

    Luhan Guest

    Must have repaired several hundred units back in the 60's. All ran in
    the A-B region. Just biased to conduct slightly at zero signal to
    avoid the dreaded 'crossover notch'. The last place you want
    distortion, is near zero.

    Luhan Monat (luhanxmonat-at-yahoo^dot^com)
    http://members.cox.net/berniekm/
    "Reality: what a concept!"
     
  14. Phil Allison

    Phil Allison Guest

    "Tim Williams"


    ** Such arrangements are generally known as "zero bias, class B" - never
    called class C.

    Many famous high powered audio amps have the output devices biased off and
    rely on the drive devices to "fill in" the missing bit in crossover region.

    The Crown DC300A is one example.

    The Quad 405 "current dumping amp" is another.




    ........ Phil
     
  15. GregS

    GregS Guest

    I don't think I was ever impressed by their home amplifiers weight, allthough
    it usually goes by price. Switching, probably not. Most of these cheap
    amp have overdriven transformers, so they skimp.

    greg
     
  16. Jon

    Jon Guest

    Many current designs use the brute force transformer-rectifier-filter
    approach. However, new regulations are proposed that would require all
    consumer products to meet a minimum power factor requirement. This
    requirement would eliminate the old approach in favor of switchers with
    power factor correction. Also, class D amplifiers require tightly
    regulated supplies for the output stages, which make switchers more
    attractive, since linear regulators are notoriously inefficient.
     
  17. Phil Allison

    Phil Allison Guest

    "Jon"

    = another publicly masturbating FUCKWIT !!!!

    ** There is nothing "brute force" about it.

    SM is a brute force idea by definition.



    ** Please cite your evidence !!

    I bet it does not exist.



    ** Jon is full of shit up to his fucking eyeballs.

    A wanker without a cause .......



    ** Shame about the many consumer and professional class D amps that have
    ordinary transformer based PSUs.

    Check out the Crown K series, released nearly 10 years ago, still on sale.

    Best Class D amps ever made.



    ** This "Jon" FUCKWIT is yet another know nothing, fucking asshole .

    Audio power amps do not have *linear* regulated PSUs .






    ........ Phil
     
  18. Ken Smith

    Ken Smith Guest

    I've both seen and heard class C audio. It was a PA system used for
    voice. It sounded very bad but you could understand what was said.
     
  19. Pooh Bear

    Pooh Bear Guest

    Overdriven transformers ?

    Graham
     
  20. Pooh Bear

    Pooh Bear Guest

    Actually IEC61000-3-2 let them off the hook on account of the low
    contribution from such devices.
    Power amplifiers don't use regulated supplies.

    Graham
     
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