Saurav and other amp experts...

Discussion in 'Archived Threads 2001-2004' started by Mark Austin, May 29, 2002.

  1. Mark Austin

    Mark Austin Supporting Actor

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    Could you read page three, and page eight, and let me know what you think of what is being said there? I have owned this amp for 5 months now, and love the sound, as it sounds so much different than most SS amps. Does any of what they are saying make any sense, or is it mumbo jumbo? And have you heard of a floating toroidial transformer before?
    Thanks in advance.[​IMG]
    http://www.electrocompaniet.com/support/aw120.pdf
     
  2. Saurav

    Saurav Cinematographer

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    LOL!!! I'm no amp expert! In fact, one of the real experts got banned recently [​IMG]
     
  3. Mark Austin

    Mark Austin Supporting Actor

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    You did build your own amp didn't you? You're an expert, as far as I'm concerned. Thanks for your reply. [​IMG]
     
  4. Saurav

    Saurav Cinematographer

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    Only modified my amps, thinking of building some soon. Built a preamp, but from a kit, so someone else designed it. Built a phono stage and a crossover and some speakers, but they were all someone else's designs. I'm hardly an expert [​IMG] Glad to be of help though.
     
  5. Brad_Harper

    Brad_Harper Stunt Coordinator

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    What is said on page three is nothing new. Any good solid state amplifier design needs negative feedback in all three of the major amplifier stages as well as global feedback. It is the only way to truly compensate for differnces in transistor construction. Look at the schematics of a Bryston or a Pioneer and you will see feedback in all three amplifier stages.
     
  6. Larry B

    Larry B Screenwriter

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    Brad:
     
  7. Saurav

    Saurav Cinematographer

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    Here's how I understand it:

    If a designer can get by without using local or global negative feedback, that's great.

    Global negative feedback shouldn't be used to accomplish what should have been done using local negative feedback.

    Just like any other blanket statement, saying "Using negative feedback is bad" is fairly naive. In other words, bending over backwards and compromising other factors just to eliminate feedback isn't going to produce good-sounding equipment. All it'll do is allow a "No negative feedback" line in the marketing literature.

    Which isn't a comment directed at Ayre. It's just like any other commonly held misconception in this hobby - many people have a subconscious feeling that anything without NFB must be better than anything with NFB. That is simply not true.
     
  8. Larry B

    Larry B Screenwriter

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    Saurav:

     
  9. Saurav

    Saurav Cinematographer

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  10. ling_w

    ling_w Second Unit

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    So how does Ayre get a decently flat open loop gain w/o feedback of any kind? Create a highly capacitive output impedence so as to act as a frequency modifier for the next stage?

    In any case, does this not cause phase shift across the audio bandwidth. All for lower TIM?
     
  11. Saurav

    Saurav Cinematographer

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    I believe Charles Hansen posts at Audio Asylum (www.audioasylum.com). You could post a question to him there, if you like.
     
  12. Kevin C Brown

    Kevin C Brown Producer

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    Very stupid question:

    I remember reading sometime back (mid 90's), that the reason why a certain-part-of-the-world's amps sounded so bad was because they used negative feedback. But, by using negative feedback, you got really good measurements.

    Maybe supports what Saurav is saying...

    The comment was in reference to Threshold and their Stasis design. (No or very little negative feedback used in that case.)

    And, I'm curious too. I have taken some (entry level) EE and transistor (CMOS and bipolar) classes, but no mention of negative feedback. Maybe amplifier circuit design? (Didn't get that far, just the solid state physics of it all...)
     
  13. Larry B

    Larry B Screenwriter

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    Ling:
     
  14. Saurav

    Saurav Cinematographer

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  15. Brad_Harper

    Brad_Harper Stunt Coordinator

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    In the world of amplification Negative feedback is "good". Amplifiers work by comparing the signal that is at the output to what is coming into the amplifier and amplifies the difference. The only way for this to happen is to have feedback from the output to the input. All amplifiers I have designed or seen designs for have operated this way. Another important application of negative feedback is the "Beta" matching of internal transistors. Not all transistor of the same brand or make are exactly the same each has a different "Beta" value. Inside solid state amplifiers it is important that the differential amplifier stage has transistors that are matched so the input and output can be compared accurately. Since exactly matching transistors is next to impossible negative feedback is used to negate the effects of not having matched transistors. Plus on the output stage negative feedback is used to keep the transistors from oscillating and destroying your speakers.
    I really have no idea how Ayre creates an amplifier without using some sort of feedback. I would be very interested to see their schematics.
     
  16. Saurav

    Saurav Cinematographer

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    Maybe they do it with no global negative feedback, but use NFB within amplifier stages? I don't know, I'm just guessing here. I doubt the schematics are freely available, but like I said before, anyone interested can quite easily post a question to the designer on the AA forum.
     
  17. Brad_Harper

    Brad_Harper Stunt Coordinator

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    I just read the features of the Vx-1 amplifier on the Ayre website. From the sounds of things it is using a two stage amplifier system instead of the more common three stage. By using a two stage they could get away without using global feedback, but the components would have to be chosen very carefully to ensure very closely matched "beta" values. The two stage amplifier still uses a differential input stage so some feedback is still required in the first stage of the amplifier. From the looks of things more engineering went into that huge power supply then into the amplifier. The profit on that amp must be huge.
     
  18. Aslam Imran

    Aslam Imran Second Unit

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  19. Saurav

    Saurav Cinematographer

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    Does it matter?
     
  20. Kevin C Brown

    Kevin C Brown Producer

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    Well, "beta" is a parameter only valid for bipolar transistors. (Sort of the "gain" or efficiency of the device.) I also know that where I work, "transistor matching" is very important... [​IMG] (Chips not for audio, but for telecom.)
     

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