Fascinating interview with Class D inventor Bruno Putzeys

Discussion in 'Audio Hardware' started by head_unit, Feb 18, 2018.

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  1. head_unit

    head_unit Senior Member Thread Starter

    Location:
    Los Angeles CA USA
    Well, maybe not original inventor, that was actually Al Gore :p (or was it Halliburton?).
    Bruno Putzeys: Head of the Class (D, That is)
    Among other things, he says (my paraphrasing) that Class D didn't sound better because designers didn't do the hard math. I can absolutely relate to that, as I've had various speaker design colleagues who could design very nice speakers and drive units by cut-and-try but really didn't understand the math and didn't understand magnetic fields except crudely. Bruno also says "The correct list of items in the playback chain in the order of importance is: Room acoustics, speaker acoustics, drive units, then a long void followed by electronics as a remote third. " and that (my paraphrasing) all this fiddling around with different amps and preamps and such is just not a good approach to making better sound (but, I'd note, keeps a lot of companies in business, and a lot of audiophiles psyches intrigued...)
     
  2. Helom

    Helom Forum member

    Location:
    U.S.
    S&V: Generally speaking, what are the key benefits of Class D versus the traditional Class AB and Class A designs that have long been favored by audiophiles?
    BP: Efficiency and therefore the ability to construct amps that are powerful for their size. Only that. Modern Class D amps, in particular mine—ahem—sound good not because they’re Class D, but in spite of it. I can’t repeat that often enough. Left to its own devices, a switching power stage tries to do just about anything except amplify audio
    .
    Read more at Bruno Putzeys: Head of the Class (D, That is)

    Wow, even the class D Guru admits the the only advantages are efficiency and size.
     
  3. Ham Sandwich

    Ham Sandwich Senior Member

    Location:
    Sherwood, OR, USA
    I've still yet to hear a Class D headphone amp.
    I'm not aware of any pure headphone amps that are Class D.
    Little amps like the PS Audio Sprout are Class D and have a headphone jack. But I don't know if it is using a separate headphone amp circuit or is using Class D for the headphone amp.
     
  4. beowulf

    beowulf Forum Resident

    Location:
    Chula Vista, CA
    :laughup: ... that should be warning signal in and of itself! :laugh:
     
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  5. Helom

    Helom Forum member

    Location:
    U.S.
    The one advantage he failed to mention is increased profit margins for the manufacturer.
     
  6. GoldprintAudio

    GoldprintAudio Forum Resident

    Location:
    Lexington, NC
    But is that really a bad thing? If there are Class D options that sound equally as good as it's A/B competitor, and they weigh 15 to 20 lbs in monoblock form (versus say 70 or 80lbs in a class a/b version for similar power output), along with having much less energy consumption, would that not be a good thing?

    I know I would much rather mover around 20 lbs versus 80.....
     
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  7. head_unit

    head_unit Senior Member Thread Starter

    Location:
    Los Angeles CA USA
    Is the Sprout the one with the non-defeatable 70 Hz boost?
     
  8. head_unit

    head_unit Senior Member Thread Starter

    Location:
    Los Angeles CA USA
    Really? Maybe, but I feel doubtful that is so true for equivalent performance. Maybe cheaper that a brick-outhouse Class AB, that could be so, since as he alludes to there is actually disadvantage to putting in oversized parts. One fellow at an Audio Engineering Society meeting I attended said the same exact thing.
     
  9. head_unit

    head_unit Senior Member Thread Starter

    Location:
    Los Angeles CA USA
    Yeah, I think the tone of @Helom's post takes Putzey's comment out of context. His "admission" in no way is an admission of inherent inferiority. And if I was touring, I'd sure rather truck and lift slim amps than the old school 130 pound Crests, Crowns, etc.
    Now what I would like to ask Bruno is "how about Class D versus Class G/H" like the lovely QSCs I used to use, or the BASH stuff. Although someone correct me if wrong, but I *think* their idle efficiency is nowhere near as high?
     
  10. Helom

    Helom Forum member

    Location:
    U.S.
    How does it take the comment out of context? At no point did I say that any class AB amp is inherently superior to any class D amp. I was merely pointing out what came straight from the horse's mouth, that the only advantages are size and efficiency, even for his particular designs, which he insinuates are the only ones that perform well.

    To quote Bruno again: Modern Class D amps, in particular mine—ahem—sound good not because they’re Class D, but in spite of it. I can’t repeat that often enough.

    Even though I didn't mention inherent inferiority, that quote sure alludes to it.

    What does touring have to do with hi-fi in a domestic setting? Now that's taking the topic out of context.
     
  11. Helom

    Helom Forum member

    Location:
    U.S.
    I suppose if you want to look at it that way. I have no qualms with moving my 65 and 50 lb amps. Bruno's comments do suggest that only his designs are worthy options.
     
  12. sunspot42

    sunspot42 Forum Resident

    Location:
    San Francisco
    Both of which are massive advantages. I'd also add cost, and ability to drive difficult loads. My new Pioneer Elite SC-LX501 with its D3 amps sounds scads better than the old (I assume class A/B) h/k receiver it replaced, has over double the power output, and can drive 4 ohm loads. Something which would shutdown the h/k. Also runs cooler. Doesn't weigh less, but doesn't weigh considerably more, and only cost I think $100 more than its predecessor.

    I'm surprised Class D amps haven't completely swept the middle of the market at this point - they clearly offer more value for money, which in my book is the only metric that matters. Well engineered, they certainly don't sound worse than any A/B competitors in their price class, and they have numerous advantages. It's a no-brainer.

    Although the real advances are probably going to come when powered speakers - with their own digital crossovers and Class D amp per-driver - become more prevalent. I think that's where the maximum audio bang for the buck can be had, because these designs can be perfectly tweaked for flat response and to overcome as many phase issues as possible.

    My new Pioneer receiver is an example of this - it has a phase control for the subwoofer, in my case a sloppy old Klipsch 12" unit that I keep saying I'm gonna replace, but never do (good subwoofers are expensive and I'm cheap and live in an apartment - my neighbors probably wouldn't like a new sub very much). Now I'm glad I didn't bother, because the Pioneer makes this sloppy old thumper sound like a much tighter unit from SVS or similar. Remarkable difference, and I can imagine how effective similar precise phase control - plus sophisticated digital crossovers and equalization - would be up in the middle of the audio spectrum on a precision engineered speaker/amp combo.
     
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  13. onlyconnect

    onlyconnect The prose and the passion

    Location:
    Winchester, UK
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  14. Helom

    Helom Forum member

    Location:
    U.S.
    They certainly do to my ears, but to each his own.
     
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  15. sunspot42

    sunspot42 Forum Resident

    Location:
    San Francisco
    How many modern Class D amps have you listened to?
     
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  16. Helom

    Helom Forum member

    Location:
    U.S.
    More than I can count on all my toes and fingers.
     
  17. Mike from NYC

    Mike from NYC Senior Member

    Location:
    Surprise, AZ
    And how many did you audition in your home for a few days? Using equipment you are familiar with and using speakers that are correctly positioned according to your ears?
     
  18. HiFi Guy

    HiFi Guy Forum Resident

    Location:
    Lakeland, FL
    If it's a Sprout, yes. If it is the Sprout II (from Massdrop) it dropped the non defeatable bass boost.
     
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  19. Mark broadhead

    Mark broadhead Forum Resident

    Location:
    Newcastle England
    I think Brunos comment alluded to the difficulties in designing out the problems in switching amplifiers. He has done an admirable job to my ears. However they are ruthless with upstream components.
     
  20. BIGGER Dave

    BIGGER Dave Forum Resident

    The only Class D amp I own is a Fender bass amp. 350 Watts @ 4 Ohms. 13” x 3” x 7” and just 6 pounds. Maybe a vintage Ampeg SVT 300 watt tube amp has the sonic advantage, but since it weighs in at 80 pounds, I’ll take my 6 lb Fender Rumble 350 head anyday. Why risk a hernia if you don’t need to? Class D amps make great bass amps because unlike guitar amps, bass amps usually run undistorted.
     
  21. Helom

    Helom Forum member

    Location:
    U.S.
    Every one I've heard, regardless of the room, speakers, source, vehicle, weather, and Chinese calendar year had a cold, forward, analytical, and ultimately fatiguing sound. The midrange always seemed boosted as though someone took an equalizer and cranked the 1 to 2KHz bands.

    This was not only with home audio amps, but mobile audio as well. The car audio brands all claimed to had cracked the class D nut as well, but more or less, all of them retained the sonic signature I described above.

    That's what I've always noticed with Class D, whether it was a cheap AVR or the $15K Devialets. Maybe there's an exception out there somewhere but I have yet to encounter one.

    I really could care less what technology an amp employs if it sounds good. I've owned a few class D amps and auditioned many more because I try to approach each one with an open mind. Some were better than others but I couldn't live with any of them for long. I personally don't think the tech is quite there yet, which is why I found Bruno's comments especially interesting. I did hear a NAD integrated recently with the NCore modules, and it was good for class D, but I still noticed that forward, boosted midrange quality.

    That's my experience in a nut shell. Fair enough?

    Edit: the above doesn't apply to subwoofer amps. I think they work great for that application.
     
    Last edited: Feb 19, 2018
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  22. Manimal

    Manimal Forum Resident

    Location:
    Southern US
    That’s my whole thing, are we getting the cheap option at high prices.
     
  23. Helom

    Helom Forum member

    Location:
    U.S.
    That's what I believe. Some of these amps are mostly free space inside. Not only do they save money with a smaller chassis and fewer parts, they save on shipping costs too. It doesn't appear to me that these savings are being passed on to the consumer. So why are folks touting cost as an advantage?
     
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  24. Manimal

    Manimal Forum Resident

    Location:
    Southern US
    I’ve always stated in post concerning class d that I’m sure from what I’ve read it can sound great.. can’t it? I’ve heard Merril stuff is awesome.
    And I’ve only heard the Sphinx (hybrid) auditioned in my home against my lowly CJ Sonograph SA 250. Had a audiophile buddy over and asked him to say nothing during the listening session. He was not conditioned to the CJ like my ears are. No contest was our conclusion. Now Im a base model audiophile so that was it for me (price range) on any class D.
    Now I’m sure the bucks could close in and kill the old CJ, but for now....I’ll stick:)
     
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  25. sunspot42

    sunspot42 Forum Resident

    Location:
    San Francisco
    But do any measurements actually reflect this boost? Because I'm not aware of any.

    Maybe the issue is class A/B amps are coloring the sound, and you've grown used to that coloration.
     
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