AW: To earth, or not to earth...

Don Tillman don at
Wed Dec 3 20:17:25 CET 1997

   Date: Wed,  3 Dec 97 09:27:27 PST
   From: Tim Cockram <tim at>

   Don on "dustbins":
   >It also suffers from other opamp problems; noise, rising output
   >impedance with frequency, offset voltage, etc.  

   Good points Don.  It does work in practice (in several high
   broadcast mixers (high end) and I belive on the chroma voice

(Not in the Chroma voice boards that I can see.)

	    If you use the op-amps output for a reference ground (that
   scheme is used in some Harrison desks) you could run in to the
   problems you have described but if you just connect stuff like leds
   or even logic to the output you transfer the garbage (hence
   dustbin) to the supply rails not the real ground.

Ahh I see... use the opamp to drive the ground for the noisier stuff
only leaving the proper ground for the more sensitive circuitry.

Yes, that's a completely fine approach.

  -- Don

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