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Thread: Nelson Pass B1 preamp build

  1. #81
    Bigman80 Guest

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    Quote Originally Posted by RothwellAudio View Post
    If they're both connected to the chassis, they're commoned.
    Ah, so how else do I do it?

  2. #82
    Bigman80 Guest

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    This is what I'm thinking. How do I get rid of it?
    Quote Originally Posted by RothwellAudio View Post
    Yes, the 0 volts doesn't have to be connected to mains earth. If it is, there's the chance of creating an earth loop (depending on what other equipment is connected to it).
    I prefer to link 0V to the chassis via a 100 ohm resistor.

    In this case I don't think the problem is an earth loop. It sounds to me like the case forms a complete loop around the transformer when the case lid is on and it's creating a magnetic pathway.

  3. #83
    Join Date: Apr 2012

    Location: N E Kent

    Posts: 51,624
    I'm Geoff.

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    Non-Ferrous lid?

  4. #84
    Bigman80 Guest

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    Quote Originally Posted by walpurgis View Post
    Non-Ferrous lid?
    Not simple enough Geoff lol,

    Transformer shield?

  5. #85
    montesquieu Guest

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    Quote Originally Posted by walpurgis View Post
    Non-Ferrous lid?
    That's what I was thinking. Nice thick sheet of black perspex. Maybe that's why I'm not an engineer.

  6. #86
    Join Date: May 2012

    Location: Toulouse, France

    Posts: 6,562
    I'm Kevin.

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    Have you tried it without the transformer shield?
    Kevin

    Too busy enjoying the music....

    European loan coordinator for Graham Slee HiFi system components..

  7. #87
    Bigman80 Guest

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    Quote Originally Posted by RothwellAudio View Post
    Shouldn't be necessary. The world is full of preamps with steel enclosures - they don't all hum. Correct wiring should make it immune to picking up hum. I suspect a large loop somewhere which is acting as an induction loop. Star earthing is all about eliminating loops and is why it's favoured.
    Tell me more. How would you approach the earthing

  8. #88
    Bigman80 Guest

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    Quote Originally Posted by CageyH View Post
    Have you tried it without the transformer shield?
    There isn't a shield, Kevin. It's just a potted transformer. The outer casing is plastic

  9. #89
    Join Date: Apr 2012

    Location: N E Kent

    Posts: 51,624
    I'm Geoff.

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    Mumetal box? I'm just saying the first things that come to mind. Could all be rubbish (or not).

  10. #90
    Bigman80 Guest

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    Quote Originally Posted by walpurgis View Post
    Mumetal box? I'm just saying the first things that come to mind. Could all be rubbish (or not).
    Well, I used one in the DIY phonostage which has a larger TF and the casework is steel. I didn't get any hum in that case. Might be worth a punt.

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