Quasi or Fully complimentary

Discussion in 'General Audio Discussion' started by Vitopanch, Apr 27, 2007.

  1. Vitopanch

    Vitopanch Super Member

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    Hail,
    My tech , who is working on one of my power amplifiers, has asked me as to whether I want it to be Quasi or Fully complimentary. He is a great tech, but weak in the area of explanation, hence I ask yall.

    My questions are, does each have it's benefits, or is one better than the other and why please.

    Vito
     

     

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  2. Jukin Jay

    Jukin Jay Geek

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    Is the tech designing from scratch or repairing? This isn't something that is trivially changed on-the-fly.

    Quasi-complementary uses two output transistors of the same type (both PNP or both NPN) in series between the supply rails, with the load connected to the midpoint of the series-connected pair, the collector of one and the emitter of the other.

    Fully complementary design uses one NPN and one PNP transistor in series, with the load connected to the midpoint, both emitters connected together.

    Quasi-complementary was popular early on with germanium transistors as it was easier to manufacture PNP than NPN transistors. Manufacturing techniques improved rapidly with the use of silicon, making it possible to produce both NPN and PNP transistors closely matched in characteristics other than polarity.
     
  3. maxkelley

    maxkelley Wiremonkey

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    In English, I think it means go fully. :drool: As Jay said, though, why would you need to change it if it was being repaired?
     
  4. goldear

    goldear Certifiable Audio Junkie

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    Thia question does not make sense if he is simply "repairing" your amp. This sounds like a major modification involving a complete re-design of your driver and output stages. As mentioned above, this is not a trivial change, and would involve a essentially redesigning of your amp.

    If you want your amp to work the way that it originally did, and not to be a completely different amp, then tell him to: "keep the original design".
     
  5. Pilot

    Pilot Active Member

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    Generally speaking, fully complementary is better provided you have the correct matching transistors. However, quasi complementary can be as good with the Baxandall modification which places a diode across the emitter resistor of the lower driver transistor, so that the base-emitter junctions of the output transistors look balanced to the drivers. This gets around the increased crossover distortion. (Sorry for the technical gabble there, but you did ask).

    Bryan
     
  6. Vitopanch

    Vitopanch Super Member

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    Thank you for the responses. The tech is rebuilding a power amplifier for me whose transistors are missing.

    Is there a benefit to one design over the other? Is one more reliable or produce better sound? I usually like to keep things original, it is quasi now, however, if there is a significant advantage of one over the other, that will influence my answer to him.

    Vito
     

     

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  7. mhardy6647

    mhardy6647 AK Subscriber Subscriber

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    http://www.lacieg2s.ca/w3terra/ols/scott260.htm

    There are those who are quite enamored of the quasi-complementary topology (i.e., I don't think that the article referenced above is meant ironically -- you might want to look at some other articles from the site before you reach a conclusion, though!)
     
  8. Vitopanch

    Vitopanch Super Member

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    mhardy6647,
    Many thanks. What could be better than a H.H. Scott article on the subject. I searched for awhile before asking here. Much appreciated.

    Vito
     
  9. backmd

    backmd Active Member

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    Quasi-complementary was popular early on with germanium transistors as it was easier to manufacture PNP than NPN transistors.

    Actually I believe that it was easier to manufacture NPN rather than PNP transistors so that quasi complementary has a pair of NPN transistors.
     
  10. Doug G.

    Doug G. Addicted Member

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    You are correct, sir!

    NPNs were better than PNPs.

    And, actually, this even extended into the silcon era as the early silicon PNPs were still not as stable as the NPNs.

    Heathkit famously used the quasi design in their power amps and I think they sound great.

    EDIT: Hehe. Finally, after four years, this has been corrected! Think of all the hundreds of poor souls who wandered around with that misinformation in their heads all those years.

    Doug
     
    Last edited: May 30, 2011
  11. JoeESP9

    JoeESP9 ESL's & tubes since 83

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    That's some tech you've got. It sounds like he's going to redesign the output stage of whatever amp he's working on.
     

     

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  12. Doug G.

    Doug G. Addicted Member

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    He must be a "quasi - tech"

    Ba dum bum.

    Doug
     
  13. nashvillebill

    nashvillebill Super Member

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    Now, I don't know how burnt up your original amp was, but if it worked at all...

    This would be like taking your car in to get new tires. The salesman asks you "do you want me to make it an automatic transmission or stick shift?" But then he can't explain what you have or what he's going to do or why it needs changing.

    Unless you REALLY suspect your entire amp has been burnt to a crisp, and/or you are intentionally wanting him to redesign it...I'd get that amp out the shop and take it to somebody else.

    Maybe your tech is a good dude, but this sounds quite bogus.
     
  14. goat67

    goat67 AK Subscriber Subscriber

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    I think he figured it out 4 years ago :D This is an old thread.
     
  15. nashvillebill

    nashvillebill Super Member

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    Wow, nobody else even noticed the dates, I sure didn't.
     
  16. Doug G.

    Doug G. Addicted Member

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    Um, see my edit in post #10 made 4 minutes after the original.

    Doug
     

     

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  17. Artie

    Artie AK Subscriber Subscriber

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    These threads are still useful. I was trying to remember what the output topology of my old Kenwood KA-500 integrated was called, (with a pair of NPN's). Thanks to Google, I now know it's "quasi-complimentary". ;)
     
  18. chazix

    chazix AK Subscriber Subscriber

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    A quibble, but alas, Google records spelling and other errors, too: the word we want here is complementary.

    Sorry for language lawyering,

    chazix
     
  19. Artie

    Artie AK Subscriber Subscriber

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    No . . . that's good to know. This thread keeps on providing. :)
     
  20. nj pheonix

    nj pheonix AK Subscriber Subscriber

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    Do we actually know the end result?
     

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