Power supply grounding

[Don Tillman]

   From: Doug Tymofichuk <dougt at cancerboard.ab.ca>
   Date: Wed, 5 Jan 2000 10:32:18 -0700 (Mountain Standard Time)

   Unfortunately, there did not seem to be any concensus as to 
   the correct way of doing this. 

I think there was a misunderstanding about what the goals are and the
discussion drifted; I know I'm lost.  These things happen.  There are
issues of safety, hum reduction, other equipment that will be
connected, history, and so forth.

The first rule is that you want the chassis connected directly to the
earth ground pin of the line cord for safety.

Older (Beatles era) tube guitar amps had two-wire line cords and this
horrible "ground switch" to ground the chasis to one end of the line
voltage through a capacitor.  It always caused shocks, leaps, spasms
and sometimes death.  I'm really surprised this was legal; it's
certainly dangerous.  Avoid it.

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).

Often that's not practical, as input jacks are often mechanically
secured into the chassis.  In that case you have to make do and call
one point on the chassis the ground point and run all ground
connections to there.

  -- Don