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faint hum from 9V Boss switching adapter

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  • faint hum from 9V Boss switching adapter

    Just wondering if there is anything I can do to wipe out the tiny hum present. If I bypass/remove the pedal chain, the hum is gone. All four pedals are true bypass. Even one produces the hum. Should I wire the negative to a ground washer? Add filter cap someplace? Help, this is serious!!

  • #2
    Rig development

    Well, to the 9V rail added tons of extra filtering: 3900 uF. Which did little if anything. Then swapped the last cable from the pedals (now Planet Waves) heading to the amp input - this helped!

    One observation is that if I just go straight into the amp, unplug the guitar and with the bare tip, probe around the outside of the gear, I can trace some ground loops (I think that's what is happening). Moving towards the amp's power transformer casing gives some good hum, the loop's eq/effects grounds give a tiny bit too. Especially near their power supplies. Grounding the tip at the input jacks gives near-total silence.

    Unsettling after all the work to build, what I thought, might be a deadly , pro rig. It is quite bearable though as this Hiwatt is well behaved noise-wise, aside from that dang PT! It even seems to be interacting with Bill Lawrence single coils which are normally very quiet.

    Any ideas?

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    • #3
      What is the model number of the Boss 9v supply?

      Have you tried using a linear 9v supply?

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      • #4
        Boss Model: PSA 120s

        I had a transformer based one before and these are better on all accounts as far as I can tell. The pedals' ground meets preamp ground at the input jack.
        I suppose each pedal get a serial ground connection through the short cables as the single moves along right? They're all true-bypass.

        Maybe a massive-guage 3 prong power cable for the amp will help.

        thanks.

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        • #5
          I think the PSA-120 is rated at 200mA? How much current are you pulling with all of the pedals? If you are close to the 200mA the psa 120 could be noisy around the upper current limit?

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