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Avondale NCC300 amp project ..

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

  1. laverda

    laverda pfm Member

    The trans are what Les supplied, AST jobbys. 530va 2 x 42-0-42 = 60vdc rails to the outputs (both secondary paralleled) and the front end from this main board supply via the links to the regs. With luck I'll be listening to it later today....
  2. flashgo

    flashgo DIY Practitioner

    Those ASTs are a perfect match for the the Holden & Fisher in the 135. Do they have the extra windings for the fan circuit?

    I forget how high a voltage the NCC220s can take, but it could be interesting to take them up a notch with that AST.
  3. laverda

    laverda pfm Member

    Hi Flash,

    Yes, theres additional winding for the fan....I believe. I don't think the 220s will take 60v or were designed to do so..the 300 has the additional devises which allows the extra volts..

  4. LesW

    LesW Retired at user request

    Graham, check the pinout of the BD237, the base is not the centre pin
  5. laverda

    laverda pfm Member

    LOL, I was just looking at that Les and was going to drop the 2n5551s back in.
  6. chiily

    chiily PFM Special Builder

    Fabulous... I wish I could 'do' wiring so neat...
  7. laverda

    laverda pfm Member

    I have one amp board set to 2.2v and the output 15003 & 4's are warm, at 2.5v their getting nice and warm...Domesticity now in place, so play stops till tomorrow. :(
    Last edited: Mar 12, 2018
  8. mirkov

    mirkov Active Member

    When available I'd like to try this NCC300 and integrate a pair with my NCC220s as they are now flying after more than a month of burn-in, due probably to wrong choice of caps bypass. (wimas...)
  9. RJHarker

    RJHarker pfm Member

    I'm an EET with 4 135's to play with, I can help with development. What I gotta do? Sign an NDA?
  10. laverda

    laverda pfm Member

    Up early and back at it ....final checks with the sig gen. and scope all good (just on one channel to start with) ....offset 1.5mv bias 2.2v. Hooked it up to a pre and JR149's the other end...

    very bloody good indeed..more to report later on, I've never heard these little speakers sound this good. I'll let it play for an hour or two and re-test, then on to the other channel.

    The 2k7 I changed to 3k3 and the 2k2 I dropped to 1k2 but this is too much...as with these two changes the bias is off to +3v which translates into very hot output devices in short time. Other changes were tried as I had a little difficulty in gaining more than 1.0v bias at first. Which it turned out to be my error by installing the DB237 incorrectly. (advised by Les see previous post.)

    So just change the 2k7 to 3k3 and with this there is plenty of available bias if wanted..2.5v is too much IMO as the spreader gets to warm after only a 5-10mins.

    The next thing of note is the silence, (Flash is right when he said darkness) even at switch on the faintest pops hardly detectable through the speakers (no speaker protection at this stage) and then a total absence of noise from the tweeter with ones ear up against it. At first I thought the amp wan'nt powered up...but it was and a gentle twist of the vol knob.. provided the proof it was working.
  11. LesW

    LesW Retired at user request

    Graham, to say I'm pleased for you is an understatement - I'm like a dog with two tails
    hearing the news. Although the NCC200/220 have very little residual noise, I hoped the
    current mirror configuration plus fully complimentary output strategy of the 300s might
    reap rewards - it seems very much like it has. Don't you love it when a plan comes

    Congrats on a job well done Graham........
    flashgo and orangeart like this.
  12. LesW

    LesW Retired at user request

    In that case my dear fellow, you'd better email me with your bona fides. les@avondaleaudio.com
  13. 337alant

    337alant Negatively Biased

    Wow what a cracking job :cool: and very pleased its sounds great as well

  14. Marra

    Marra pfm Member

    +1 on that.

  15. RJHarker

    RJHarker pfm Member

    Credentials sent!
  16. laverda

    laverda pfm Member

    A quick helper for those building at a later date...

    There are no test points for the bias setting so leave one leg clear on both 15R resistors off the PCB so when it comes to setting bias voltage its easy to attach the probes.


    Be extra careful when soldering the legs, MJE15030, MJE15031 ZTX753 & 653...its a bit tight.

    Last edited: Mar 14, 2018
    bugbear likes this.
  17. flashgo

    flashgo DIY Practitioner


    You've got your transistors flying high above the PCB. What's your reasoning?

    (I also discovered the trick of popping up the resistor legs to use for test points. Along with that, DMM leads with small spring-loaded hooks came in invaluable on this build.)

  18. laverda

    laverda pfm Member


    I leave the 753 635 just a bit high to get some cooling .....I tend to leave a bit of space 'just in case' = just in case I need to pull them at a later date, its much easier with a bit of leg to work with. Ive never found that being tight against the board improves anything, or a detriment. But always willing to learn..

  19. flashgo

    flashgo DIY Practitioner


    I'd noticed that Naim gradually brought the trannies closer to the board over the years. For no particular reason, I'm in the middle ground with enough leg to accommodate a hemostat during soldering.

  20. flashgo

    flashgo DIY Practitioner

    Here's the next NAP135 prior to the rebuild. Of the original Naim amps, the 135 was always my favorite. There were only a few modest changes on the original board in this photo. When seen side-by-side with the NCC300/SPM1 rebuild, one can appreciate the brilliance of Les' repurposing.

    Last edited: Apr 13, 2018
    Mike Hanson, chiily and divedeepdog like this.

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