[sdiy] Distribution board bypass caps?

[David G Dixon]

I don't put decoupling capacitors on my distro boards.  I put them on
individual modules -- 10uF electrolytic on each rail, plus one or more 100nF
ceramics.  I connect the distro board to the PSU with 14-gauge stranded
wire, across a terminal block with crimped-on connectors for easy
disconnection.  The traces on my distro boards are quite wide, and I usually
tin them by hand with solder to thicken them (although I'm sure this is
quite unnecessary).

So far, I've had no problems with rail noise.

 

> -----Original Message-----
> From: synth-diy-bounces at dropmix.xs4all.nl 
> [mailto:synth-diy-bounces at dropmix.xs4all.nl] On Behalf Of Oscar Salas
> Sent: Tuesday, January 17, 2012 10:10 AM
> To: James Coplin; Synth DIY List
> Subject: Re: [sdiy] Distribution board bypass caps?
> 
> Yes , good question, I'm also thinking about it these days.
> 
> I think that must be considered the resistance of the cable 
> that connects the power supply to the board, and also the 
> resistance of the traces of the board, if connectors are 
> placed as a bus. 
> 
> For example if Distribution Board
> is close to the Power Supply and the cables are short and 
> thick, so low resistance, it will no needed decoupling 
> capacitors at all.
> 
> In the other hand if cables are
> long and thin, so a considerable resistance, maybe you will 
> need big filter capacitors in order to avoid any noise, or 
> undesired signal in the audio range, looping through the 
> modules to the distribution board.
> 
> Also must be considered that big
> capacitors will increase or create inrush current. However if 
> cables have considerable resistance, they will limit it. 
> 
> So I think that the idea is, to more (power supply to 
> distribution board) cable resistance, more big capacitors.
> 
> This is my thought. 
> 
> More ideas?
> 
> 
> 
> 
> 
> ----- Original Message -----
> From: James Coplin <james at ticalun.net>
> To: Synth DIY List <synth-diy at dropmix.xs4all.nl>
> Cc: 
> Sent: Tuesday, January 17, 2012 5:51 PM
> Subject: [sdiy] Distribution board bypass caps?
> 
> If I have a distroboard for 10 5u modules, what would be the "correct"
> size for bypass caps?  I don't know what the exact draw of 
> the modules will be so I need something to reasonable cover a 
> "typical" case.  The supply is a 3A supply and there will be 
> 4 distro boards total in the system although as some modules 
> are double width, I'll never have 40 modules installed.
> 
> James R. Coplin
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