Power supply grounding

[Don Tillman]

   From: Martin Czech <martin.czech at intermetall.de>
   Date: Fri, 7 Jan 2000 09:40:32 +0100 (MET)

   Don:
   :::The second rule is that the signal ground inside should be kept
   :::separate, but at some point connected to chassis ground with a
   :::low-value resistor (under 100 ohms).

   I wonder what will happen if someone touches the singal ground
   (jack) and there is a short fault, some high voltage to signal
   ground.  I guess a current divider between 100 Ohms and the body.

"Shit happens."  :-)

Connecting high voltage to the signal ground will likely blow up that
resistor, but only if there's nothing else connected to ground.
Typically there is other stuff connected to signal ground and sparks
will fly.

   All guitar stuff schemos I've seen (only a few) show signal ground
   tied to protective earth and chassis in one point, with no intended
   resistance...

Generally yes, the input jacks typically connect the signal ground to
the chassis.  But I think that's mostly historical.

Most quality mixers, such as the Mackie models, have differential
inputs, which effectively separate the signal ground from the chassis
ground if you use an XLR connector or stereo 1/4-inch plug.

  -- Don