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    Ground Shocks

The Ground switch on a classic Fender^® amplifier can sometimes result in a shock when you touch the amp or a vocal mike.  The following circuit diagram shows how the Ground switch is attached directly to the AC power line.

The Ground switch inserts a capacitor between the amp's metal chassis and either side of the AC power line.  The purpose of the capacitor is to drain off any noise from the AC line that could cause the amp to buzz.

In one position of the Ground switch, this capacitor connects the hot side of your house wiring to the chassis of your amplifier (see the red path in the diagram).

This presents a shock hazard because it allows the amplifier chassis to float at a voltage that isn't even neutral, much less ground.  Since your guitar's metal parts and strings are an extension of the amplifier chassis, being connected through the shield of the guitar cable, you too float at a voltage that isn't neutral.

To eliminate the shock hazard, the Ground switch should be removed, as shown below.  For added safety, install a 3-wire AC cord to insure that the amp's chassis (and therefore your body) are always hard-wired to the electrical system's ground.

If there's a 2-pin extension outlet on your amp's rear panel, you might want to leave it there but disconnect it.  If you must use it, consider replacing it with either a 3-wire or a polarized, 2-wire outlet.

If you want to keep the line filter, consider installing a 3-position Ground switch, as diagramed below

You can set this switch to the center-off position most of the time.  Install a "locking" switch to insure that it doesn't accidentally toggle.

WIRING NOTES:

1. AC cords use a black wire for hot, white for neutral, and green for ground.  The neutral wire goes to the wider prong of the AC plug.  The hot wire goes to the narrower prong of the plug.
   
   
2. For safety when changing fuses, connect the AC cord's hot wire to the fuse holder contact farthest from the fuse cap.
   
   
3. If the power transformer's primary coil has one black wire and one white wire, use the black wire for hot. Otherwise use either.

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