[sdiy] keeping signals seperate..avoiding noise

[Simon Brouwer]

I agree it would require special attention to guarantee good contact
between the panels and the mounting rails. E.g. using stuff like this:
http://nl.farnell.com/chomerics/82-121-74006-g8701/gasket-foam-1m/dp/1218458

In a semimodular, with only a single front panel, it is of course much
easier.

If you connect each individual panel to ground and if they are not
isolated from each other you will get ground loops. Grounding all panels
together from a single point to the star point, as I proposed, you won't.

In practical systems it may be more desirable to avoid the risk that some
panels are not grounded than avoiding those ground loops. So I'm not
saying that per-module panel grounding is a bad approach, however it is
not ideal either.

Laurie Biddulph schreef:
> The problem with this method is that it assumes that you will get a `zero
> ohm' contact between each panel and the module rail. In reality there will
> be layers of dirt and oxidation on the rail surface, the panel surface,
> the
> fixing screw surface and no guarantee that inserting the screw will
> provide
> good contact between the module and the panel.
>
> Grounding each panel through its attached pcb means that the panel will be
> at true ground potential (assuming no losses etc through the boards and
> power cables) and that all panels will be at the same potential. This
> means,
> ideally, that the panel would be grounded through either a dedicated
> ground
> power rail (PANEL GND = PGND) or as close to the power connector on the
> attached board. I believe Oakley modules do the PGND approach although
> they
> also assume that you do not have a 100% MOTM compatible module in the
> system
> (MOTM do not split the grounds on the power connector so can't offer a
> true
> PGND connection). Oakley assumes the 2nd option where he gnd is made at
> the
> power connector (I think).
>
> In my Panther modules there is a ground strap provided on the pcb that is
> used to ground the associated panel. I don't have PGND (not an option in
> Doepfer compatible systems) and make my panel connection as close to the
> front edge of the pcb as possible for manufacturing convenience.
>
> Best Regards
>
> (Mr) Laurie Biddulph
> Phone: +61 (0)2 4340 0938
> Mobile: 0400 257 645
>
> Elby Designs
> ABN: 70 022 727 605
> http://www.elby-designs.com
>
> This e-mail and any files transmitted with it are confidential and
> intended
> for the addressee only.
> If you are not the addressee you may not copy, forward, disclose or
> otherwise use it, or any part of it, in any form whatsoever. If you have
> received this e-mail in error please notify the sender and ensure that all
> copies of this e-mail and any files transmitted with it are deleted.
> Any views or opinions represented in this e-mail are solely those of the
> author and do not necessarily represent those of Elby Designs.
> Although this e-mail and its attachments have been scanned for the
> presence
> of computer viruses, Elby Designs will not be liable for any losses as a
> result of any viruses being passed on.
>
> Please consider the environment before printing this email
>
> ----- Original Message -----
> From: "Simon Brouwer" <simon.oo.o at xs4all.nl>
> To: "sdiy" <synth-diy at dropmix.xs4all.nl>
> Sent: Sunday, November 16, 2008 8:57 AM
> Subject: Re: [sdiy] keeping signals seperate..avoiding noise
>
>
>> Seb Francis schreef:
>>> Justin Owen wrote:
>>>> -----Original Message-----
>>>> From: Laurie Biddulph [elby_designs at ozemail.com.au]
>>>> Subject: Re: [sdiy] keeping signals seperate..avoiding noise
>>>>
>>>>
>>>>> As a matter of good construction, the power supplies for each board
>>>>> should be run direct to the main power supply in
>>>>> what is sometimes referred to as `star' fashion. Daisy-chaining from
>>>>> one board to the next will allow noise induced on
>>>>> to the lines from one board to be radiated to the others.
>>>>>
>>>>
>>>> Would the same apply to pots wired as volume controls - i.e. where one
>>>> pin goes to Earth/Ground?
>>>>
>>>
>>> No, it only applies when you are drawing current, especially current
>>> spikes, as then the resistance and inductance of the power line causes
>>> the voltage along it to fluctuate.  It different circuits share the
>>> same
>>> power line, the spikes will then couple between them.
>>>
>>> For panel controls it may be better not to use star-earth if they are
>>> also earth-connected through a metal panel as you could get ground
>>> loops
>>> (=hum).  When using shielded cable it is normal to connect the earth at
>>> 1
>>> end only to avoid ground loops.
>> IMO in synthesizer modules the ground of a module should never be
>> connected to its metal panel. The panel should be isolated from the
>> module. The panels should be grounded by connecting one point of the
>> mounting rails to the star point.
>>
>> --
>> Vriendelijke groet, Simon Brouwer.
>> | http://nl.openoffice.org | http://www.opentaal.org |
>>
>> _______________________________________________
>> Synth-diy mailing list
>> Synth-diy at dropmix.xs4all.nl
>> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>>
>
>
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at dropmix.xs4all.nl
> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>
>


-- 
Vriendelijke groet,

Simon Brouwer
-*- nl.openoffice.org -*- http://www.opentaal.org -*-