HARDONE Kit - HUM when external powered

    Hi everybody,
    I mounted the Hardone kit and it sounds very good with battery alimentation, but when I use an external power it works but it also hums very loud. I followed the exact layout on pdf.
    If I switch off it doesn't hum anymore.
    I've tried 3 different external transformers but it hums the same with each.
    When powered with the external transformer it hums also without any signal in input.

    Any suggestion?

    Thank you

    a non-ideal power supply causes hum in such simple electronic circuits like the hardone. There is not much feedback in the circuit and thus power supply noise rejection is poor. Even if you use three different supplies, how can we know, whether these have any value or quality. Are you using DC or AC supplies? Some description would help a lot. Just for a try you could connect a 100 Ohm resistor between dc input and C3. This should make things a lot better. Connect a diode in series as well and you may even be able to use an AC supply (not recommended at all).

    hi walter11, I use dc supplies, I've tried another good switching ac/dc converter and the HardOne is now working without any hum. thank you for the suggestions, I'll try the 100ohm resistor.

    ciao
    Mauro

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