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Naim NAP250 Advice

Discussion in 'd.i.y.' started by imarks, Feb 15, 2021.

  1. martin clark

    martin clark pinko bodger

    Well done!

    And thanks for the great write-up with photo - very helpful for anyone else in future who searches for this, and esp your point of view and findings.

    Now just enjoy it some more :)
     
    imarks likes this.
  2. jpk

    jpk pfm Member

    Well done! So the golden caps don't need to be replaced...?
     
  3. onlyconnect

    onlyconnect pfm Member

    I get the impression that you are better at this than me :) but the first time I did this I managed to damage the fascia which is quite fragile. Luckily I was able to replace it with a genuine part but that was a while back.

    Tim
     
    imarks likes this.
  4. Gervais Cote

    Gervais Cote Predator

    If this was my amp and these caps were electrolytic, I would replace them all upfront. No need to be an axial type, many radial ones can be used, you just have to bend the leads to fit in place.
     
  5. martin clark

    martin clark pinko bodger

    That's a good point, but for all the things 'wrong' with the regulator design* - a quick look at the schematic shows it is not sensitive to the status/quality of that 47uF axial cap.

    That cap, one per rail, is used to pre-filter the feed to the zener reference: and even if the axial cap at , say ESR >+10ohms and cooked in old age - ripple at say 0.5Vrms at the reservoir caps only (nominally) rises to c. 100uV on the reg ( - based on simple approximation at 100Hz.)

    So - fortunately - it's much less critical than the axial 10uF parts for sure :)



    * @PigletsDad has posted detailed analysis on this, in last 3-5yrs. tl;dr: the whole regulator design is 'upside down' and that gives up 20-30dB of potential performance - but to gain that margin requires homebrew & testing of something entirely different. You cannot get there by simple parts mod on the original PCB.

    So when the factory layout works well-enough to please most people, most of the time - and is as demonstrated above , easy enough to service even by people new to opening-up their power amp - I'd suggest ...don't worry about it. If you love your NAP250 / NAP135 as it is - it is very, very easy for you to keep things that way.

    :)
     
    imarks and Gervais Cote like this.
  6. jpk

    jpk pfm Member

    Jeff did that, see this thread. I built his regulator board and can confirm it sounds very good and clean:

    [​IMG]

    As today mains are more polluted (than in the 70s) the improved rejection of his version is welcome.
     
    Last edited: Feb 24, 2021

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