[jason]

On 6 Jul 2014 09:11:40 -0400 "Scott Dorsey" wrote in
article

In article , Trevor wrote:

Most of the modern mixers with inbuilt supplies are switch mode, so the
transformer is small, light, and operates at high frequency, so little
problem putting them in the box now.

That makes the noise issues even worse!
Now instead of something spewing 60 Hz magnetic fields into your quiet
electronics you have something spewing high frequency magnetic fields
AND electrical fields all over.

Take a look inside one of the newer Allen and Heath cheapies and look at
some of the extreme measures they've had to go through to keep switcher noise
under control. It's beautiful work.
--scott

+1

The tiny, Verizon-branded phone charger in my car completely obliterates
FM reception when it's charging the phone. That takes some doing! I
presume it's a switcher - the clunky old one didn't behave like that.

For fun, I took the charger inside and hooked it to to a battery; I can
hear a raucous buzz on every ham band from 1.8 through 50 MHz. Winding
half a dozen turns of the wire around a split ferrite core pretty much
killed the noise. It makes me wonder if there are any EMC compliance
standards for these things.

Switching supplies make a lot of sense but without care a lot of noise,
too. A new culprit: PV panels with integrated inverters. It's a good idea
to boost the voltage right at the panel to reduce losses, but panels on
the roof are probably pretty good antennas. (I can hear one such
installation on a house a quarter of a mile from mine. I've been working
with the owner to figure out how to mitigate the issue. Fortunately, he's
receptive because he was "hearing something strange" on radios in his
house.)