[sdiy] RFI filters on bipolar supply

[Magnus Danielson]

From: Dave Magnuson <resfreq at hoohahrecords.com>
Subject: [sdiy] RFI filters on bipolar supply
Date: Thu, 06 Sep 2001 15:04:24 -0400

> Hi List,

Hi Dave,

> I'm building a second power supply for my modular, since I've outgrown my
> current one.  
> 
> I have an IEC connector that I scavanged from an old laser disk player...
> and it has built in RFI noise suppression on both the hot and neutral
> lines.  It's comprised of 3 caps and 2 inductors.  Starting at the input of
> the connector, one cap connects between hot and neutral, then there's an
> inductor in series on each line, followed by a cap to ground on each line.
> 
> Would it be a bad idea to use this?

No. It is not a bad idea. However, the caps will cause a minor leakage
which you can "feel" when you draw a finger over the metalic hood on
some boxes. This is usually not a major trouble in audio
applications, but is very good to know that it happends. Note that
this leakage is there even if the power is off, that is because the
power switch follows after the filter, and this is how you should design.

> I figure any added RFI/EMI suppression
> would be good, but I don't know if there's going to be any problems
> connecting this to a typical 7815/7915 based bipolar supply.  I figured
> it's free, so I might as well use it if it'll work. 

The typical 78xx/79xx supply should have no trouble.

Indeed. I buy such connectors with filters when I need them. Extra
cost is minor IMHO.

So, I recommend them, but one should be aware of the
leakage. Naturally should one connect the signal ground with the
protective ground.

Cheers,
Magnus