[Scott Dorsey]

In article , Mike Rivers wrote:
On 2/9/2018 6:16 PM, Gareth Magennis wrote:
I suggested to Linda that the hum might actually be coming from the SMPS
wall wart, not the cabling.

I said that to check that, she could try connecting a different power
supply.

There isn't anything in a COMMERCIAL, APPROVED switching mode power
supply that can cause hum. They're surprisingly clean. Finding a
suitable substitute power supply, unless she'd bench-equipped like Phil
and me and maybe you is likely to be difficult. You need the right
voltage, pretty close to the right current, and the correct size plug
wired with the proper polarity.

I am skeptical, Mike. I spend much of my day tracking down RF noise coming
out of crappy switching supplies. It's true that good clean switchers do
exist, but it's also true that you're likely not to find them at the music
store or at Wal-Mart.

If a piece of gear hums by itself, that's an equipment problem. If you
get hum when you connect it to something else, that's a system problem
and there are many places to look for solutions. In my experience, a
power supply is a possible offender, but there are other places to look
for trouble - which may include isolating the power supply from the
common system ground (which may not be the brown stuff under the house).

Indeed, this is true. Switching supply noise does not sound like a hum.
Distinguishing hums, buzzes and hisses is half the struggle.

The original poster claims to have a hum.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."