Re: USB hum/noise isolation?

On Mar 11, 2:59 pm, "StudioDog" <i...@xxxxxxxxxxxxxxxx> wrote:
...
The next question: Does your building actually HAVE valid grounds?

As far as I know. All my equipment runs into a Belkin power bar
(supposedly with RFI/EMI filters as well as surge protection), and the
Ground light on the bar indicates the presence of a ground.
...

I have disconnected and unplugged everything but the computer and the
mixer and the noise persists. There is no noise on the built-in
Realtek HD Audio card, though. I may have to go analog to avoid the
noise. (I did instal a USB2.0 PCI card to try to isolate the USB ports
from any computer/electrical noise, but had no luck here either).

Does everything have three prong plugs? When you say you
disconnected everything but .. everything means even disconnecting
power cord. IOW do you put those other items on an isolated power
source such as a UPS that is only running on internal batteries? If
not, then that wire is also carrying signals - you did not disconnect
everything.

The Belkin provided only enought EMI/RFI filtering to make a claim.
Put numbers to that claim and Its filtering is zero. Also one
potential noise carrying wire through that Belkin must have no
filtering as required by human safety. Don't think of it as a magic
box. Think of it in terms or each seperate wire inside that Belkin.
Think in terms of each wire; not in terms of boxes.

Isolation - every electronic device must already contain an
isolation transformer or something equivalent. It is required for
human safety. That isolation would only address differential mode
noise. Noise can exist by coming down one wire and returning on the
other. Or noise can exist by coming down only one wire and continuing
through. Two completely different noise modes. Three AC electric
wires. Different units see one signal / noise and not the oher even
when both modes exist. Without this simple concept, then all you can
do is keep buying magic box solutions.

To get anything more than a 'try this and try that' response,
diagram every connnection. That means listing each of three wires in
the AC cable because even that may define connections for different
noise modes. That means listing which USB wires are and are not
used. USB has four wires. You need to know that.

USB is not just a signal wire. Does your mixer use power wires on
that USB; or only use balanced signal wires? To get an answer that
can target the problem, know things at that level of basic detail.
Only alternative is to keep changing things and spending money until
noise diminishes to an acceptable level.

Ground - your household wiring is 100% best. 27 year old wiring
would be same as 1 year old wiring. For this problem, irrelevant
whether a building safety ground exists. What matters is a single
point ground that you apparently established on the power strip.
Everything that connects to an entire system - everything - must get
power only via that strip. Nothing can be grounded or connected to
anything else - even touch baseboard heat . Otherwise that is another
connection that is not through the power strip. Anything else
conductive (tabletop, floor, etc). Then these also must be connected
to the Belkin safety ground and added to your diagram of wire
connections.

For useful replles, what is connected to what must be defined in
terms of every wire in every cable. For example, computer and mixer.
Computer connects to power strip. Mixer connects to power strip. USB
connects between them. Right there are mutliple wires that could be
an electrical loop - reason for noise. Question is whether a common
mode noise is using that loop. In theory, differential mode noise
would not onduct if mixer and computer only used signal wires in USB
cable. But USB cable is four wires. How do the other two wires
connect?

Above is the simplest way for layman to solve a noise problem.
Nothing posted is technically complex - requires any training.
Everything posted is at the layman level - except EMI/RFI claims from
Belkin which uses deceptive claims. Otherwise keep buying and trying
things randomly.

.

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