Ground Switch: Not needed with 3 prong cord?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Nolatone Ampworks, Jan 4, 2008.


  1. Nolatone Ampworks

    Nolatone Ampworks Silver Supporting Member

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    Hi all,

    I have an amp opened up looking at it. It's a Fender style amp.

    The ground switch isn't even connected.

    Looking at the schematic, I get the impression that with a modern 3 prong power cord, that switch is irrelevant and not needed.

    Am I right?

    Thanks,

    Paul
     
  2. LZ_69

    LZ_69 Member

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    You got it,
     
  3. teleamp

    teleamp Senior Member

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    Back in the two prong plug days the chassis was "grounded" to earth via the neutral line in, since there was no telling how the receptacles were wired (if Bubba was left handed or right handed, hot on left side, neutral on right side or vica versa) the ground switch let you reverse the polarity, on the older amps with no ground switch you just had to flip the plug around. Like how the old refrigerators would shock you if they were plugged in wrong, Thank God for the NEC.

    MikeY
     
  4. GDking

    GDking Member

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    use a single coil guitar, turn the ground switch off, and then sing into your microphone with the PA plugged into another outlet.

    Let me know how you make out :)

    (don't stand in water when you perform this test)
     
  5. Nolatone Ampworks

    Nolatone Ampworks Silver Supporting Member

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    Yep, I had an old Magnatone that had that problem! I ended up marking the plug with tape so I know which way to flip it when plugging in!
     
  6. AdmiralB

    AdmiralB Silver Supporting Member

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    Ground switches and three-conductor power cables have NOTHING to do with each other. Amps started getting grounded cables circa 1970, give or take, but many had ground switches as recently as the mid 1990s.

    Ground switching is a noise reducing technique. With a capacitor that's actually designed for that application, it's perfectly safe and is occasionally useful.
     

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