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The Dynaco Tube Audio Forum

Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Tubes4hifi VTA tube amp and preamp kits and all products

    Hum problems in completely rebuilt PAS-3X


    Posts : 4
    Join date : 2008-12-25
    Age : 68
    Location : Umea, Sweden

    Hum problems in completely rebuilt PAS-3X Empty Hum problems in completely rebuilt PAS-3X

    Post by Swede52 on Sun Feb 22, 2009 1:19 pm

    I have rebuilt an old PAS preamp but I got a hum problem that I don't know how to solve. According to one person you have to do everything exactly by the book (manual). In that case PAS:es are nothing for DIY-ers and that, of course, would be a pity if you ask me. Some things confuse me about this and I don't yet know how to explain them. For example, I get hum when using the phono input even when it's shorted! Would you believe that? I thought that had to be impossible... A shorted input should not produce hum, should it? I think the problem might have, at least partly, another source than unorthodox wiring. For example, using the low level inputs I get a weak 50 Hz hum just by plugging the cable into the wall outlet (the ST-35 that I use for testing is already warm but the PAS is off and cold). Anyway, I'm lucky there's no hum at all from the preamp when using line level inputs when they are shorted or loaded and that is what this amp is going to be used for. CD:s, tuners and cassette decks... No records player although I kept the phono input. Anybody has any clue to a solution? I would be most grateful...

      Current date/time is Mon Oct 26, 2020 5:32 pm