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Naim Nait3 Recap

Discussion in 'd.i.y.' started by istari_knight, Dec 19, 2011.

  1. istari_knight

    istari_knight pfm Member

    Evening all :)

    Recently took a peek inside my Nait3 to see if anything was "going off" Being an eBay buy you never know... Everything looks ok apart from the thermal compound on the outputs has gone hard & powder like so that'll need sorting. However the biggest issue is the three main power supply capacitors namely: 2xBHC Aerovox 10000uf 40v 1xBHC Aerovox 4700uf 40v. They are all bulging & look ready to burst but I cant find any suitable high quality replacements. I purchased some 10000uf 50v Kendeils but they are too tall for the slimline case :mad:

    Any advice greatly welcomed ! Cheers.

    PS. Bias across emittor resistors reads 2.6mv(left) 3.1mv(right) - Would it be correct to adjust them to around 5mv ?
  2. sam_cat

    sam_cat C'est Crounchifique!

    What height/diameter are the current ones?
  3. lennyw

    lennyw Still throwing Eephus pitches

    As a Nait3 owner I'd appreciate some images of yours explaining the issues -- something for me to look out for. Thanks.
  4. neiljadman

    neiljadman Senior Member

  5. MJS

    MJS Technical Tinkerer

    Caps are max 35mm tall. Get them from Farnell:

    1679495 CAPACITOR, 10000UF, 40V, 35X35 KEMET ALC10A103DC040

    You can't get the 4700 from them but have used BC Vishay equivalent to great effect.
    1165578 CAPACITOR, 4700UF, 40V VISHAY BC COMPONENTS MAL205657472E3

  6. sojourner

    sojourner pfm Member

    I just recapped a Musical Fidelity A200 with six 10,000uF 40V BC Vishay caps. They were the only ones I could find that actually fitted and were rated over the 35V of the originals (supply rails are at 37 to 38v). It sounds fine and the ESR was nice and low - Farnell supplied.


  7. istari_knight

    istari_knight pfm Member

    Thanks for the help chaps. I'll have a look at what Farnell has to offer...

    I wont be doing any major mods, just a little preventative maintenance - It currently sounds fab with some Royd Minstrels which I intend to upgrade the crossovers but thats a whole 'nother thread!
  8. istari_knight

    istari_knight pfm Member

    Okay, just ordered some new caps so thats my Christmas project sorted.

    Another question: what rectifier is the Nait3 supposed to use for the power amplifier board ? Mines got a "KBU10M" fitted & looks rather dodgy with its legs all twisted to fit the through holes... I think someones been in here before me :rolleyes:

    Not sure how I missed that before!

    Edit: Found it on google, BR62... Looks like someones "upgraded" the original
  9. istari_knight

    istari_knight pfm Member

    I decided to go for some Nichicon "KL" as they were half the price of others yet still made by a reputable brand. KL is part of the low profile series and they are exactly the same size as the original BHC Aerovox.

    LennyW mentioned earlier in the thread that pictures could help others identify potential problems in their Nait3's so I took a few snaps whilst doing the work.

    Here is the Nait in question, not the best looker but I love her :)


    These are the original BHC Aerovox capacitors that have bubbled on top & didnt appear to be charging as they should (From flicking the power switch on the back there was a 6 second delay before hearing a pop from the speakers.) They were promptly replaced with the new Nichicons.


    Now, onto the dried up heatsink compound... This stuff is supposed to aid thermal transfer between the output devices & the heatsink. In its current state it will be hindering thermal transfer causing the outputs to get hotter than desirable which can end in a destroyed output stage (Trust me I've been there with an old Marantz receiver!)


    I removed all of the old thermal compound with some rubbing alcohol on a cotton pad, it just falls right off using this method.


    Now all nice & clean with new thermal compound, I use Dow Corning 340 but 99% of white silicon compounds will be fine. Never use silver compound designed for CPU's as it can be conductive I have also thrown away the old mica insulators simply because I couldnt be bothered to clean them & fitted new ones (TO-220) One small "dob" of compound either side of the mica & we are ready to reassemble.


    Here you can see the non standard rectifier fitted by the previous owner, the original is 6A whereas the replacement is 10A so I decided to leave it....For now.


    I then left it turned on with no source or speakers connected for 20mins before setting the bias. Measured across the 0.22R emitter resistors & set to 4.5mv either side.


    Result ? A much healthier sounding Nait! The bass was quite anemic prior to the TLC whereas now its as every Naim should be :cool: Hopefully that helps a little :)
  10. Pete MB&D

    Pete MB&D Pete Maddex, the one and only!


    Nice job.

    I replaced a faulty rectifier in a Nait 2 with a higher rated one, and the oner said it sounded better than before, so I would be inclined to leave it in.


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