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Naim Gain stage - Feedback vs Gain

Discussion in 'd.i.y.' started by pm1961, May 25, 2005.

  1. pm1961

    pm1961 pfm Member

    I vaguely remember reading that somebody experimented with the value of the feedback resistor in the gain stage with good results.

    If I remember the logic correctly, reducing the feedback increased the gain (and quality?) but its natural limit was the overall stability of the circuit.

    Has anybody any details of experimenting with this?

    Cheers,

    PM
     
  2. LesW

    LesW Making electronics make music

    A combination of a 6K8 and the existing 1K will virtually halve the gain of the stage. To ensure stability, a 47pF ceramic or silver mica cap across base and collector of the ZTX214 will guarantee the stage doesn't do it's usual impression of an RF signal generator.
     
  3. pm1961

    pm1961 pfm Member

    Does your answer infer that you believe the gain is already as high as stability would allow and there's nothing to be gained by decreasing the feedback?

    Is that cap across the trannie a "good thing" irrespective of any other changes?

    Cheers,

    Paul
     
  4. LesW

    LesW Making electronics make music

    In the main, with any given circuit, as the feedback is increased, the stability is degraded ( there are phase shift issues which are responsible for oscillation ). With the gain stage in question, it's a very good idea to fit that small cap and indeed, after many years of doing just that, I had to smile when Salisbury followed suit. Funnily enough, I've just finished work on an Ixo which when powered up, raved away like a good 'un - the caps put paid to that malarky.
     
  5. Mick P

    Mick P Retired and content

    Les

    You mentioned Salisbury........they don't mention you (at your request) so do the honourable thing and return the compliment.

    Regards

    Mick
     
  6. LesW

    LesW Making electronics make music

    You know Parry, I've never been targetted by a stalker before - I must say it's really quite flattering to learn that I must be treading on a few toes .........
     
  7. muzzer

    muzzer Numb Nut

    seconds out!!:eek:
     
  8. Mick P

    Mick P Retired and content

    Les

    It is very simple really. I shall remind you every time you mention Naim.

    My PC flashes when it happens so its dead easy and very effective.

    If you don't mention them, my pc dosen't flash.

    The ball is in your court as they say.

    Regards

    Mick
     
  9. fatcat

    fatcat pfm Member

    Mick

    A couple of strobe lights and Klaxons in and around your home would surely be more appropriate.
     
  10. RustyB

    RustyB Registered Ginga

    Gee Mick, I bet Les is shaking in his boots.....not!

    This is the DIY section, Les is offering useful advice, why don't you just PISS OFF!!!
     
  11. LesW

    LesW Making electronics make music

    I'm sure everyone's impressed by your flashing Michael. Speaking for myself though, I prefer to roll my own.......
     
  12. Mick P

    Mick P Retired and content

    Rusty

    To answer your eloquenty put question, Les can answer as many questions as he likes and I hope he answers hundreds. All I am doing is drawing attention to the fact that he is once again having a snipe at Naim.

    He has asked them never to mention him so he should do the decent thing and not mention them.

    Regards

    Mick
     
  13. laverda

    laverda pfm Member

     
  14. Tony L

    Tony L Administrator

    A little perspective please – as I understand it Les has informed Naim that he does not want mentioning on their forum, a place where, as far as I am aware, he does not have any right of reply. This situation has absolutely nothing to do with pfm, plus no one who works for Naim is banned on this forum, they have full access to state their case here if they don’t like something Les says. These are very different situations.

    Tony.
     
  15. Basil

    Basil Harbethian


    Are we talking R9 and R14 here Les?


    BTW Les, huge thanks for all your help over the last 2 years, I couldn't be happier with the results.

    Steve.
     
  16. Jo Sharp

    Jo Sharp Pulls on doors marked push

    Les,

    I take it this is the same position as the 33pf cap you used to recommend (on the Analogue Addicts mailing list IIRC)?
     
  17. yairf

    yairf pfm Member

    I second that.
    Les has been a tremendous help for me, whether he mentioned Naim or not.
    Yair
     
  18. Mike Hanson

    Mike Hanson -=> Member

    Yup, Les is a great chap, which he's proven to me a number of times now. He's not the fastest of the bunch, but that isn't always the most important thing now, is it?

    -=> Mike Hanson <=-
     
  19. Stuart Frazer

    Stuart Frazer pfm Member

    Les W

    I for one enjoy reading your posts, along with many others. Please carry on and ignore the snipes from Parry.

    Stuart
     
  20. Linnik

    Linnik Flat Earth - Source First

    Seconding for Les!

    Mick, Les DID NOT mention Naim as you stated. He mentioned Salisbury.

    Perhaps you should train your evaluations when to react and when not and get your PC to service if you have asked it to bling when Les mentions Naim. It is a faulty thing as it is blinging on Salisbury, too. Or perhaps it blings even for Les? Get it checked if you lean on your PCs evaluations. It may spoil your reputation (?).

    This time Les did not really put Naim anything much into shame and there was no reason for you to come in the middle. BTW what are you doing in the DIY side? After all this is for tinkerers, ehh?

    We all have our personal shortcomings and you would not stand such a stalker yourself on your neck, would you? Les has done massive positive contribution for most of the DIY people here.

    We all know how splendid amps Naim manufactures and how good after sales service they are offering. They speak by themselves. Les is in his own class and Naim do not give a toss about Les or anybody else, I bet. No reason to make too much hassle on it here either.

    Oz
     

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