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Avondale NCC300 amp project ..

Discussion in 'd.i.y.' started by laverda, Feb 28, 2018.

  1. laverda

    laverda pfm Member

    I made a visit to Avondale towers yesterday and came away with a few bits which included some NCC300 PCBs..

    I've made a start but I'll have to order quite a few components before I can really get going and complete the build.


    I'll keep you posted on progress ....As a starter I'll be building monos running the whole board off 50v rails via 530va 0-35 0-35 transformers and minicap6's. Later I'll split the front end off and power that separately as in the voyagers.
    chiily, torstoi and divedeepdog like this.
  2. Marra

    Marra pfm Member

    You can't do this to me!! I haven't even finished my Qudos.

    Going to be following with interest.
    Last edited: Feb 28, 2018
  3. keithsnaim

    keithsnaim Gone Fishing

    Now that does look interesting. I've been wondering what to build next. Good look and keep us well posted. I will have to pop over to see Les now that he is much better.
  4. Chops54

    Chops54 pfm Member

    Laverda, do you have the specs for the ncc300? I'm more interested in power output with decreasing loudspeaker impedance.
  5. chiily

    chiily PFM Special Builder

    Oh bugger...

    So, Les how much for a pair of PCBs?
  6. laverda

    laverda pfm Member

    Sorry no. I'm sure Les would enlighten you on specs though..120watts/8Ohms at a guess, dependant on transformer rating and rail voltage etc...
  7. Chops54

    Chops54 pfm Member

    Thanks. I do need to pay Les a visit anyway.
    Mynamemynaim likes this.
  8. 337alant

    337alant Negatively Biased

    YNWOAN and torstoi like this.
  9. 337alant

    337alant Negatively Biased

    As usual with Les the boards are superb quality and a delight to work on
    First job is to get the front end regs built and tested, you should have an adjustable reg if its working properly
    For general resistors I used the Takman Rey ones from HFC and some dale RN 55 & 60 where I already had them
    For the resistors in the singnal path I used none magnetic tantalums and Shinkos
    Feedback cap is an 82uf Vishay mil spec wet tant as I had them already
    Lytics are Nichicon fine gold and HG

    Last edited: Mar 10, 2018
    Bourneendboy likes this.
  10. laverda

    laverda pfm Member

    Woo Hoo..

    Nice work Alan..some late info for those interested ..

    RC1 & 2 & both c-comp locations not used (for a later date)


    The axial 2u2 63v is a mil spec tant
    The 10uf 63v is a litic and a couple of resistor revisions as per the NCC220.

    Build the regs up first and test...
    Built the front end and test/set up bias without outputs which is measured across the base legs of the MJE15031 & MJE15030 (or 15r resistor end) twiddle bias adj until 2v is measured.
    Build up outputs ...set bias.

    Bit shallow on detail but more to come.
  11. Chops54

    Chops54 pfm Member

    Would an NCC200 type VBE suffice for front end regulation?

    Delete that, I can see it has its own on board regulation.
  12. laverda

    laverda pfm Member

    But the on board regs would benefit from their own transformer / PSU (There is a jumper location between front end and output side)
  13. 337alant

    337alant Negatively Biased

    Good luck on your build and thanks for the update I have 27r in RS1&2 so would be easy to swap out.
    Any details on the resistor revisions?.
    For the output transistor decoupling caps I recon you could experiment with lots of combinations, low ESR are normally required here
    I wasn't sure about these caps but concluded they must but for a similar effect as the Accoustica mod so I stuck in a 470uf x 63V S&T axial electrolytic and a 1uf ERO KP1839 poly prop, anyway its easy to change them out for whatever works best and the amp would run without anything in there anyway.

  14. GWM

    GWM Lost in the 70's

    Oh I am surprised I though Les was not making these available for diy, interested to hear how they sound compared to Qudos.
  15. laverda

    laverda pfm Member

    This is very much a work in progress for those who have the privilege of having the bare boards in hand. I'm sure there will be questions to Les as these DIY builds progress. Though it looks to be straight forward so far.. Ha, Famous last words.
  16. GWM

    GWM Lost in the 70's

    Yes will follow with some interest my Qudos are sounding really good now they are well broken in.
  17. flashgo

    flashgo DIY Practitioner

    I just completed my first NCC300 NAP135 rebuild. It's just one amp so far, and it's only been playing in my test rig for an hour (iPhone input + Kef 101 output), but it's the best I've ever heard in this rig, and that includes Voyagers! The first thing that struck me is that the sound just comes out of total darkness. Already, I can tell that it has that Voyager grip and dynamics, and more. :D

    Per consultation with Les, it's running 55V regulated on the front end and 59V unregulated on the output end. It does not have a separate power supply for the front end. I'm tempted to run a rebuilt 250 with NCC220s and HCR200s in a similar configuration.

    I'll report more as I get there. It's going to take a bit to free up another 135, but the NCC300 boards are all built up. Hopefully, I'll be able to report on the stereo sound in a real system in a couple weekends.


    Just to reinforce how good this sounds, I'm listening to the mono test rig in preference to my main man cave stereo system. Amazing!
    Last edited: Apr 13, 2018
    Mike Hanson and torstoi like this.
  18. TOR

    TOR pfm Member

    Looking great Flash, snug as a bug in that 135! I’m feeling the itch to build... are the boards generally available from Les?
  19. 337alant

    337alant Negatively Biased

    Nice Job Flash
    I see you have the speaker protection boards in there as well, did the heat sink come in one piece for that & the NCC300 ?

  20. orangeart

    orangeart KJF Audio Ltd.

    Do we know much about this new circuit yet?


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