Ground-Loop-Like hum from nearby wall wart

[Ron Hardin]

I finally found the source of audio hum running through a system of
Behringer mixers and digital filters - a wall wart lying atop a 12v power
supply wire running to one of the filters (everything is powered off the same
12v supply, except the mixers).

The situation was improved by adding isolation transformers but not eliminated.

It was cured completely by relocating the wall wart away from the 12v wires.

Apparently the wart's magnetic field introduced a ground potential difference between the
device running off that wire and the other devices on the same power supply, giving
a ground loop.

Isolation transformers around the device helped but did not affect the hum added to
the +12v non-ground wire, which was smaller but remained.

Conclusion, keep wall warts away from the power supply output leads.
--


On the internet, nobody knows you're a jerk.

[jakdedert]

Ron Hardin wrote:
> I finally found the source of audio hum running through a system of
> Behringer mixers and digital filters - a wall wart lying atop a 12v power
> supply wire running to one of the filters (everything is powered off the same
> 12v supply, except the mixers).
>
> The situation was improved by adding isolation transformers but not eliminated.
>
> It was cured completely by relocating the wall wart away from the 12v wires.
>
> Apparently the wart's magnetic field introduced a ground potential difference between the
> device running off that wire and the other devices on the same power supply, giving
> a ground loop.
>
> Isolation transformers around the device helped but did not affect the hum added to
> the +12v non-ground wire, which was smaller but remained.
>
> Conclusion, keep wall warts away from the power supply output leads.

I had a friend with a project studio back in the 80's. He kept an old
AC alarm clock on top of his amp, until I demonstrated that it was the
source of the hum he kept experiencing.

jak

[Bernard Curry]

On Tue, 31 Jul 2007 14:41:21 GMT, Ron Hardin
> wrote:

Very interesting, informative, and helpful. But what is a
"wall wart"?

I'm novice audio.

Bernard Curry

>I finally found the source of audio hum running through a system of
>Behringer mixers and digital filters - a wall wart lying atop a 12v power
>supply wire running to one of the filters (everything is powered off the same
>12v supply, except the mixers).
>
>The situation was improved by adding isolation transformers but not eliminated.
>
>It was cured completely by relocating the wall wart away from the 12v wires.
>
>Apparently the wart's magnetic field introduced a ground potential difference between the
>device running off that wire and the other devices on the same power supply, giving
>a ground loop.
>
>Isolation transformers around the device helped but did not affect the hum added to
>the +12v non-ground wire, which was smaller but remained.
>
>Conclusion, keep wall warts away from the power supply output leads.

[Todd H.]

Bernard Curry > writes:

> On Tue, 31 Jul 2007 14:41:21 GMT, Ron Hardin
> > wrote:
>
> Very interesting, informative, and helpful. But what is a
> "wall wart"?
>
> I'm novice audio.

Wall wart is slang for the power transformers that are rectangular and
integrated with the wall plug. As opposed to laptop like power
supplies, or equipment that implements teh AC to DC rectification
within the chassis of the unit itself.

Any transformer or power supply is generally a source of ugly EMF, and
yes, keeping these the hell away from signal lines and chassis's is
was and always will be nearly common sense.

Best Regards,
--
/"\ ASCII Ribbon Campaign | Todd H
\ / | http://www.toddh.net/
X Promoting good netiquette | http://triplethreatband.com/
/ \ http://www.toddh.net/netiquette/ | http://myspace.com/mytriplethreatband

[Eeyore]

"Todd H." wrote:

> Bernard Curry writes:
> > Ron Hardin wrote:
> >
> > Very interesting, informative, and helpful. But what is a
> > "wall wart"?
> >
> > I'm novice audio.
>
> Wall wart is slang for the power transformers that are rectangular and
> integrated with the wall plug. As opposed to laptop like power
> supplies, or equipment that implements teh AC to DC rectification
> within the chassis of the unit itself.
>
> Any transformer or power supply is generally a source of ugly EMF,

I assume you mean EMI ? Electro Magnetic Interference (as opposed to Force - i.e
voltage)

Graham

[Todd H.]

Eeyore > writes:

> "Todd H." wrote:
>
> > Bernard Curry writes:
> > > Ron Hardin wrote:
> > >
> > > Very interesting, informative, and helpful. But what is a
> > > "wall wart"?
> > >
> > > I'm novice audio.
> >
> > Wall wart is slang for the power transformers that are rectangular and
> > integrated with the wall plug. As opposed to laptop like power
> > supplies, or equipment that implements teh AC to DC rectification
> > within the chassis of the unit itself.
> >
> > Any transformer or power supply is generally a source of ugly EMF,
>
> I assume you mean EMI ? Electro Magnetic Interference (as opposed to Force - i.e
> voltage)

Yes.


--
/"\ ASCII Ribbon Campaign | Todd H
\ / | http://www.toddh.net/
X Promoting good netiquette | http://triplethreatband.com/
/ \ http://www.toddh.net/netiquette/ | http://myspace.com/mytriplethreatband