Stompbox solid-state amp, and grounding

Discussion in 'Shock Brother's DIY Amps' started by chas.wahl, Oct 21, 2021.

  1. chas.wahl

    chas.wahl Tele-Meister

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    I've been hankering to build one of those LM386-based amps* in a stompbox, but the whole thing about how to handle grounding mystifies me. For power, there are the (usual) built-in options to stick in a 9V battery, or to connect up to a power source with a 120>12V transformer, having filtering and regulation to a battery-like (new or old) voltage.

    In the latter case, one could get a ground reference from the 120V supply, and pass that to the negative pole of the DC power out, and then ground the stompbox amp circuit to the chassis at the instrument input jack, and the chassis to the DC power-in jack's negative pole -- more or less like a modern tube amp does. But in the case of battery power, where does the ground reference come from?

    Maybe I'm over-thinking this, and should just not worry and be happy.

    *like Ruby from runoffgroove site or Noisy Cricket from Beavis Audio Research
     
  2. Gijs

    Gijs TDPRI Member

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    Battery operated equipment normally isn't ground referenced, a battery is a floating power supply. But if needed, you can stick a metal pin in the ground and connect the negative pole of the battery to it. or use a ground pin from a wall socket. or connect to a copper waterpipe.
     
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  3. 2L man

    2L man Tele-Holic

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    Mains Safety Ground is one thing and Reference Ground for signal is another!

    Modern switching power supplys do not require Mains Safety Ground because their insulation is designed good enough to isolate primary and secondary.
     
    Last edited: Oct 22, 2021
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  4. chas.wahl

    chas.wahl Tele-Meister

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    @Gijs: If a 9V stompbox amp "system" (guitar, amp, speaker) is floating, then no problem I guess; though it seems to me that one should perhaps lay out the circuitry to avoid internal ground loops anyway. My idea was that, if using a power supply starting with a three-prong L-N-G plug, I should maybe bring along the ground reference to the amp circuit.

    @2L man: I'm mainly concerned about ground reference, as opposed to mains safety ground, which I'm presuming the power supply converting to 12V/1A (self-contained) would provide for.
     
  5. sds1

    sds1 Tele-Afflicted

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    You'll get a reference off of the sleeve of the instrument cable.

    This means if you're plugged into an amp that is earthed, you're getting a reference to earth.
     
  6. Peegoo

    Peegoo Doctor of Teleocity

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    Look at most any modern wall wart power supply and you'll see there's no third ground pin. These are "double insulated" and require no mains earth ground reference.

    Pedals that use this--as well as a battery--for a power source incorporate signal ground as the ground reference and shielding/noise rejection.
     
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  7. 2L man

    2L man Tele-Holic

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    Internal ground reference comes from the circuit and its components. Stompboxes which use PNP transistors the internal ground is positive voltage and they operate just fine with boxes which use negative voltage as ground.

    Good effect power supplys both DC voltages, negative and positive float and connect cables tie effect signal grounds together.

    Instrument cabling (ground and hot) should have been upgraded to three prong (ground and two hot push/pull) very long time ago.
     
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