[sdiy] Why dual grounds?

Harry Bissell harrybissell at wowway.com
Wed Jun 9 17:38:57 CEST 2010


~most~ of the issues imho with power supply grounding come from
MODULE DESIGN and POWER SUPPLY DESIGN.

A good module design (this is what I'd say 'Paul' does)
does not corrupt its own ground or the grounds of other
modules. In this case, two ground wires in parallel have
a lower impedance, therfore better performance.

Bad board design includes sharing ground paths between
low current (reference) circuits and power grounds (things the
module designer KNOWS are going to draw high and transient
currents). Other no-no's are running power traces to high
current chips, then extending the same trace to a reference
supply. (EFM VCO4d comes to my mind here).

A good module treats the power supply as a nasty source of energy
that must be tamed and refined before it reaches any circuit that it
could disturb. Use of adequate decoupling caps, NOT using the power
rails for reference voltages, ~maybe~ ferrite beads or inductors, and
on-card regulation are good techniques.

Good power supply designs have the necessary (I'll call it)
'oompf' to be robust in supplying power. Large enough caps, etc
to handle all loads, including transients.

I've done designs that had all the jacks grounded to the front panel
(most modular designs) and also all the jacks (save one) isolated from
the panel, usually for stand-alone effects. Both techniques have their
places.

I'd say that if you are a big fan of Vactrol designs, the separate power
and signal grounds are a really good idea (Buchla anyone?)... otherwise
this is not needed

H^) harry




----- Original Message -----
From: Dave Manley <dlmanley at sonic.net>
To: Stewart Pye <stewpye at optusnet.com.au>
Cc: synth-diy at dropmix.xs4all.nl
Sent: Wed, 09 Jun 2010 11:11:29 -0400 (EDT)
Subject: Re: [sdiy] Why dual grounds?

I can't speak for MOTM, but Paul Shreiber often posts to the list.  As 
the Oakley pdf referenced by Graham indicates the two MOTM connector 
grounds are joined on the board. I'm guessing Paul would say if your 
board layout is correct, and your power distribution is good, then you 
don't need separate clean and dirty grounds back to a star point.

-Dave

Stewart Pye wrote:
> Since many of the modular synth standard power supply connectors 
> (MOTM, Oakley, Blacet etc) have two ground wires, is one of these used 
> for a "clean" ground and the other "dirty ?
>
> Regards,
> Stewart.
>
> Dave Manley wrote:
>> 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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-- 
Harry Bissell & Nora Abdullah 4eva



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