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Thread: 2-prong Metal-Framed Amps And Grounding

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    2-prong Metal-Framed Amps And Grounding

    After seeing boog’s thread on the Gibson amp with ‘death cap’ it reminded me of a nagging question I’ve had for a while and never really found a satisfactory answer for.

    I have a couple of Kenwood KA-3500 amps from around 1980 that form a part of my sound system. They feature a metal frame and 2-prong plug. I can’t see what protection there would be for the user in the event of a transformer primary burn-out to frame, other than relying on the fuse (Fe 1) to blow. The plugs are non-polarized. I had it firmly pounded into me during my apprenticeship that an appliance that is not double-insulated must be sufficiently grounded. The ‘double-insulated’ symbol is not present on these amps.

    Any insights?

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    Ce36 is the 'death cap' in this case. You could remove it and do the 3 prong addition just like you would for a guitar amp.
    edit: incorrect, no connection to chassis so not a death cap.

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    Last edited by g1; 01-13-2020 at 10:42 PM.
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    Quote Originally Posted by g1 View Post
    Ce36 is the 'death cap' in this case. You could remove it and do the 3 prong addition just like you would for a guitar amp.
    To me Ce 36 looks like an X-type EMI filter cap, no death cap because it doesn't connect to chassis ground (as far as I can see).

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    Right you are. From what is shown, it does not appear to be a 'death cap'.

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    So probably no good idea to remove it-

    (Also a death cap without a "polarity" switch would not make sense.)

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    g1, it had occurred to me at some point to simply fit a grounded cord, but I wasn't sure if it was even necessary. My perception and experience of Japanese products (hopefully not stereotyping here) is that they are well-built, well-designed, and built to last. So I figure they knew what they were doing when designing this.

    So after a bit of hunting around, a common theme for using a two-prong plug is to avoid ground loops. Modern 2-prong gear seems to be universally double-insulated. I still haven't found anything definitive on how safe this setup is and I don't want me or the wife getting barbecued.

    I'm going to whip off a cover for further inspection.

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    Last edited by minim; 01-14-2020 at 12:17 AM.

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    The big deal about it with guitar amps is that you are always holding on to the ground via your strings.
    That part of the equation is pretty much removed from many other types of electrical appliances, so we don't worry so much about them. Even plastic knobs on hifi gear means you have eliminated the biggest source of issues, contact with the chassis. That doesn't help us with guitar amps due to string grounding.
    The best possible way to eliminate shock hazards for guitar players is a wireless system.

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    Quote Originally Posted by g1 View Post
    The big deal about it with guitar amps is that you are always holding on to the ground via your strings.
    That part of the equation is pretty much removed from many other types of electrical appliances, so we don't worry so much about them. Even plastic knobs on hifi gear means you have eliminated the biggest source of issues, contact with the chassis. That doesn't help us with guitar amps due to string grounding.
    The best possible way to eliminate shock hazards for guitar players is a wireless system.
    Yes.

    I've said this before and maybe bears repeating?

    Guitar amplifiers are unique in the electronics world, where the *user* is electrically connected to the device at all times (while in use).

    The string ground may go directly to the amp chassis, or some other "ground" contact point, as in the case of isolated input jacks.

    Regardless, the user is still electrically connected to the amp in some way (and hopefully to ground thru proper wiring and a 3 prong plug)

    No other electrical appliance has this "feature" of the user connected to the appliance.
    You don't *constantly* touch the chassis of your toaster oven, TV, Stereo, Microwave, dishwasher, etc... while it is operating.

    Be safe out there....

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