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Avondale NCC300 Monos Underway

Discussion in 'd.i.y.' started by Mike Hanson, Jul 5, 2021.

  1. Mynamemynaim

    Mynamemynaim 38yrs a Naim owner

    It does indeed Alan.....

    But if I can fit it in... what's the harm in supplying the boards with the best electrons I can?
    To allow the board regs to do the best job they can?
    Cheers
    Tim
     
  2. laverda

    laverda pfm Member

    Tim, the addition of the HCR may not work, in fact it may well ‘sits’ on the sound. Too many of those good electrons can be, well, too many resulting in a blotted/tired even lifeless presentation. But please prove it to yourself though as it’s quite easy to plug in or out.
     
    Last edited: Jul 26, 2021
  3. Tarzan

    Tarzan pfm Member

    Love these threads- even if l have no idea of what is going on.:D
     
    Mike Hanson, torstoi and Mynamemynaim like this.
  4. Mynamemynaim

    Mynamemynaim 38yrs a Naim owner

    Thanks Graham (@laverda ) You know I respect your opinion highly
    Your right...if I plan it correctly, it should be easy to plug the VBE boards in or out of the power supply for the front end at will
    And as I haven't even built them (or indeed got the necessary parts!) I may well complete the amps first...but with space inside ..then try the VBE at a later date when I'm accustomed to the sound.

    @Tarzan ..glad your enjoying the thread...but it's you and me mate that haven't got a clue what's going on:D
    Im just a chancer hanging onto others coat tails and hoping for a great amp at the end of it!
    Ps
    Had a text that my cases should be here today! So that's a step in the right direction
     
    torstoi likes this.
  5. 337alant

    337alant Negatively Biased

    I think you get enough filtering from a cap 6 with an CLCRC arrangement for the front end then you have the on board NCC300 reg and a CCS & Degeneration resistors on the LTP, all for a max 20ma draw
    Alan
     
    Mynamemynaim likes this.
  6. Mynamemynaim

    Mynamemynaim 38yrs a Naim owner

    Thanks for the advice Alan..I do take it on board.... honestly :)
    The VBE is just an itch that needs scratching...and they will always come in handy on my mates ncc220 amp if found to be detrimental or no value on mine
     
    Mike Hanson likes this.
  7. Mark65

    Mark65 pfm Member

    For what it’s worth, I recently came from Avondale VBE and NCC220 to NCC300 and the difference is a major step
    Don’t think that the VBE would add anything to be honest
    If you are in contact with Les I’d ask for his thoughts
    The onboard regulators are more advanced than the VBE
    Mark
     
    Mike Hanson, torstoi and laverda like this.
  8. geoturbo

    geoturbo pfm Member

    ..just to add some sauce to the discussion.. how would a couple of high voltage alwsrs (whether being able to stand the high voltage, having enough headroom and used as preregs) behave in that position?
     
  9. nuit73

    nuit73 nuit73

    337alant and Mike Hanson like this.
  10. Mynamemynaim

    Mynamemynaim 38yrs a Naim owner


    Well yes and no!
    I know they exist because Les told me about them some time ago ..when I was asking about 300 boards..but haven't seen them

    I don't think these will be available at all to the DIY market
    Les did tell me the price he thinks a pair of complete amps in his cases using these boards will sell for.....and the figure starts with a 6
     
  11. say it as it is

    say it as it is pfm Member

    Amazing work I still have the humble 200 in the Les built 260z. Got a shiny pair of 220s to go into monos just don't have the time these days. The 300 and potentially 400 make me rather envious lol
     
    Mynamemynaim likes this.
  12. ramona

    ramona Music lover

    I've read somewhere that there gonna be a preregulator of some kind for the front end.
    Could be something simple like vbe/gyrator, I remember PD's B4 having one before 317/ 337 even though the PSRR of the circuit is quite high.

    One thing was not explained, the desertion of the preference for the FE having higher voltage than OS.
     
  13. 337alant

    337alant Negatively Biased

    I always have a higher front end voltage to the output, PD said it matters

    Alan
     
  14. Mynamemynaim

    Mynamemynaim 38yrs a Naim owner

    It's to do with the front end not "clipping" before the backend isn't it
    Higher voltage helps stop this happening
     
    Last edited: Jul 29, 2021
  15. S-Man

    S-Man Kinkless Tetrode Admirer

    I've done a fair bit or measuring of the NCC300 regs and the effect of perturbations on the FE rails.

    Firstly - the NCC300 has pretty good PSRR, especially below 40KHz, by virtue of the topology and the current sources (negative rail has better PSRR than the poitive rail)
    Secondly - Les has configured the "regs" more as filters than as very stiff voltage regulators.
    Thirdly - the Regs have a fairly high dropout voltage.

    This means that boosted supplies for the FE are quite neccessary and any extra filtering will not make any measurable difference.
     
  16. ramona

    ramona Music lover

    By extra filtering you mean in the capacitor bank by ways of added resistor / inductor ?

    I had the impression that the original circuit (RCA) had pour PSRR which Naim and the others tried to cure with regulators / oversized power supplies / additional filtering.

    Anyway, since with the introduction of NCC220/NCC300 the changes were not minor, did that change any of the tonar balance of the original NCC200 ?
    All the comments so far state 'better grip', which is makes sense, having highier bias / doubled output transistors.
     
  17. ramona

    ramona Music lover

    I hazily remember PD commenting about this but can't remember the explanation. Memory fades.
     
  18. Mynamemynaim

    Mynamemynaim 38yrs a Naim owner

    so this thread has gone a little quiet on the actual building front...so I will update my progress last night

    thanks to the kindness and generosity of certain pink fish members (thanks Martin, and Mark!) the front end supplies are finished off...and running well with 65V available

    [​IMG][/url]2021-07-29_08-51-48 by rock solid, on Flickr


    this lead on to powering up the boards and setting the regs

    [​IMG]

    58v on the front end ......55v on the back end


    then it was time to set the bias and check the dc offset ...i used Les's instructions for this

    [​IMG][/url]2021-07-29_08-49-59 by rock solid, on Flickr


    but provisionally set 110mA bias and got 7mv DC on one board and 3.5mv DC on the other one

    [​IMG][/url]2021-07-29_08-51-06 by rock solid, on Flickr


    I believe there is also a voltage way of setting the bias???
    with 2.4V being normal??
    is this like the Naim way of checking it...across the resistors?
    Anyone please?? @laverda



    I also did a bit more case work....with the transformers mounted on plywood stand offs (yerr I dont know why either?)

    [​IMG][/url]2021-07-29_08-50-42 by rock solid, on Flickr

    but it does make for a more solid mount I guess ...

    In case your wondering why I put the inner mounting plate that way up...its to do with space and mounting other / bigger boards in there later

    so apart from starting to cut the backs of the cases for the IEC sockets....thats it for yesterday
     
    Last edited: Jul 29, 2021
    divedeepdog and Mike Hanson like this.
  19. laverda

    laverda pfm Member

    The bias is set or the original way, was with a meter across RS1 and RS2, see this first photo https://pinkfishmedia.net/forum/threads/avondale-ncc300-amp-project.212730/ (the legs of the resistors are raised off the board for easier clip access) 2.4v is not the normal setting, that would be a max with enough heat sinking. I was using a 5u 400 case and it ran quite warm with 2.4v. I don't think what your using will be enough for this. But no issue just wind the bias back to 2.0v and monitor the temp over an hour or so and add more bias bit at a time ...2.05, 2.1, 2.15,... and so on. I ran mine at about 35c.

    Looking good. You’ll have these finished tomorrow.
     
  20. Mynamemynaim

    Mynamemynaim 38yrs a Naim owner

    Thanks Graham..
    What I'll do is set to 120 mA and then check and see what that corresponds to in volts at the test points you have indicated...so I have an idea how much above les's current recommendation it will be (pun intended)

    I think it might be a good bit higher....as the bias went past 200mA as soon as I switched on...and I had to act fast to "rein it in"

    My cases are small ( 2U x 300 ) but there is two of them...which makes a big difference to "all in one box"
    But I don't want to be a hero...so many well keep playing till I find a safe level that I'm happy with....it was barely warm at 110mA
     
    laverda likes this.

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