chassis grounding

[Don Tillman]

   Date: Fri, 09 Aug 96 15:59:54 PDT
   From: gstopp at fibermux.com

   Within a self-contained system such as a synthesizer I always just 
   ground everything together - the circuit board ground, the panel, the 
   jacks, the box, and the third prong of the AC power cord. Works fine 
   for me so far. I think that you only run into ground loop problems 
   when interconnecting machines together whose AC power comes from 
   different and/or distant outlets.

Yeah, but in practice something you are somehow connected to is always
powered by a different outlet (the outlet doesn't have to be very
distant either!).  A typical example would be running a feed out to
the PA; ground loop city.

The recommended approach is to ground the chassis to the third prong
of the line cord (for shielding and safety), and connect *that* point
to signal ground and power supply ground (the star ground point)
through a low value resistor, say half-a-dozen ohms.  For your phone
jacks, insulate them from the chassis and connect their ground
terminal to signal ground.
 
  -- Don