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Mini CAP 6 for NAP 180

Discussion in 'd.i.y.' started by m3trackboy, Aug 12, 2019.

  1. m3trackboy

    m3trackboy Active Member

    I have a AST 9060 dual 35-0-35 transformer from Avondale and a pair of Mini CAP 6's doing nothing.
    Can I replace the PSU in a NAP 180 without any other mods? I presume I will have to adjust the bias on each amp board.

    Also does anyone know what VA the 9060 is?

    Many thanks
     
  2. MJS

    MJS Trade: Consultant at WH Audio

    The earthing will change and the NAPA boards may not like that. You'd need to look at the PSRR noise on the output of the amp boards. If there are spikes or mains hum all over the place then it isn't optimal. Naim used a stub of purple wires on the boards 0v connection to capacitively couple to the main 0v in the wiring loom to counter such effects, if you change this even subtley then it stops working. The whole thing can be easily upset. Having said that, most of the upset was caused by their choice of transformer and power supply arrangement.

    In short; it might be ok, it might be widely unstable. If you don't have the knowledge or test gear then it's worth finding someone who does.
     
  3. MJS

    MJS Trade: Consultant at WH Audio

    Oh, and another thing, that transformer voltage rating is too high for the NAPA boards. If you replace them with NCC200/220 it'd be ok, which it was it would have been designed for.

    The NAPA boards never went higher than + and - 40v in the NAP135, and are used to around 38v in the NAP180.

    The 35-0-35 transformer will give about 48v DC at the caps, allowing for a volt or so in the rectifiers. As you can see it's not a trivial difference (20% or so). The Naim boards don't have enough headroom to work at the higher voltage.
     
  4. m3trackboy

    m3trackboy Active Member

    Thanks, I think I'll leave it as it is. I've got a couple of NCC200's part built so I think I'll make an Avondale amp.

    Many thanks
     

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