[sdiy] Why dual grounds?

[Dave Manley]

The way I've understood it: current spikes can cause the local ground 
reference to rise, since the ground connection isn't perfect and has 
non-zero impedance.  If you isolate the circuitry that generates current 
spikes (digital logic, LED drivers, 555 timers, etc) to the dirty 
ground, then the current flowing through the dirty ground can't affect 
the clean ground reference and couple switching noise into your audio path.

If you connect the two on the pcb and there is a poor connection back to 
the power supply, then the ground at the pcb can get disturbed due to 
current spikes on that board.  On the other hand if you have a separate 
path for both grounds back to the power supply, then the clean ground 
stays quiet.

-Dave

David Ingebretsen wrote:
> Thanks Paul. I've been reading about ground loops, star grounding, and other
> grounding concepts as I've been puzzling over this.
>
> David
>
> ~~ -----Original Message-----
> ~~ From: synth-diy-bounces at dropmix.xs4all.nl [mailto:synth-diy-
> ~~ bounces at dropmix.xs4all.nl] On Behalf Of Paul Perry
> ~~ Sent: Tuesday, June 08, 2010 11:43 PM
> ~~ To: synth-diy at dropmix.xs4all.nl
> ~~ Subject: Re: [sdiy] Why dual grounds?
> ~~ 
> ~~ As close to the power supply as possible.
> ~~ So there is as little 'ground' in common as possible.
> ~~ 
> ~~ Another thing to read about in grounding , is "star grounding".
> ~~ Plenty of references on the net for this ;D
> ~~ 
> ~~ paul perry Melbourne Australia
> ~~ 
> ~~ ----- Original Message -----
> ~~ From: "David Ingebretsen" > Won't these two grounds eventually have to be
> ~~ connected together though? I
> ~~ > guess that's my main question. I can layout the PCB with separate
> ~~ grounds,
> ~~ > I'm just baffled as to where/when these two grounds touch each other.
> ~~ >
> ~~ 
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