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

Tim Cockram tim at
Wed Dec 3 18:27:27 CET 1997

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In-reply-to: <Chameleon. at> (message
	from Tim Cockram on Tue, 2 Dec 97 09:47:52 PST)
Subject: Re: AW: To earth, or not to earth...
Reply-to: don at
From: Don Tillman <don at>
Organization: Don's house, Palo Alto, California

   Date: Tue,  2 Dec 97 09:47:52 PST

>   The earth "dustbin approach is also quite usefull (use an op-amp
>   unity gain buffer with the non-inverting input connected to ground,
>   the output is a goood solid ground (limited by the outputs
>   compliance).  

>(I've never heard it called a "dustbin" before!)

>It also suffers from other opamp problems; noise, rising output
>impedance with frequency, offset voltage, etc.  'Sounds like it makes
>any grounding problem several times worse!

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



Tim Cockram
E-mail: tim at 

Fax:-    UK-1222-390326


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