Audio Ground Loop Isolation XFRMR?

[dw-4]

I have a switch-box at my station which allows me to switch back and
forth between the K3 audio and PC audio.
This allows me to have SDR running on the PC and I can also listen to
the K3 in one ear and the PC in the other.

Any way, I've been experiencing ground-loop noise from my PC.
I've tried three different isolation transformers and they all work, but
with significant signal loss from the PC.
Does anyone have a suggestion?

Thanks!
N1BBR :-]
--
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[Jim Brown-10]

On Mon,9/19/2016 9:24 AM, dw wrote:
> I have a switch-box at my station which allows me to switch back and
> forth between the K3 audio and PC audio.
> This allows me to have SDR running on the PC and I can also listen to
> the K3 in one ear and the PC in the other.
>
> Any way, I've been experiencing ground-loop noise from my PC.
> I've tried three different isolation transformers and they all work, but
> with significant signal loss from the PC.
> Does anyone have a suggestion?

Yes. NO transformer is needed. What IS needed is 1) simple bonding
together of the chassis of all the equipment in your shack, bonding that
to all the other grounds in your home; and 2) get power for all of the
equipment in your shack from the same AC outlet, or from outlets whose
green wires are bonded together.

Study  http://k9yc.com/GroundingAndAudio.pdf

73, Jim K9YC
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[Robin Moseley-2]

or open circuit one of the shields  at one end..

Robin G1MHU
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[k6dgw]

The K3 has isolation transformers on LINE IN/OUT.  You don't need to add
any more.  I assume you're using the term "ground-loop problems" in the
generic [and somewhat archaic] sense.  Make sure that you're not using
the shield of any of the cables [RF or AF] as the bond between your
component's chassis' or enclosures.  They should all be directly bonded
together.  If isolating the shields with external isolation transformers
fixes the noise, that's a huge clue.

Finding the "chassis" on laptops can be a problem.  The hold-down nuts
on DB or DE connectors are often [but not always] one place to get it.
Unfortunately, those can be hard to find on some new laptops.

In stubborn cases, I'm told it sometimes helps if all the power cords
connect to the same green wire too although I've never had to go that far.

73,

Fred K6DGW
-Sparks NV DM09dn

- Northern California Contest Club
- CU in the Cal QSO Party 1-2 Oct 2016
- www.cqp.org

On 9/19/2016 9:24 AM, dw wrote:

> Any way, I've been experiencing ground-loop noise from my PC.
> I've tried three different isolation transformers and they all work, but
> with significant signal loss from the PC.
> Does anyone have a suggestion?
>
> Thanks!
> N1BBR :-]

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[Jim Brown-10]

On Mon,9/19/2016 11:40 AM, Robin Moseley wrote:
> or open circuit one of the shields  at one end.

NO, NO, NO!These are UN-BALANCED circuits. That solution only works on
BALANCED circuits.

73, Jim K9YC

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[Jim Brown-10]

On Mon,9/19/2016 12:13 PM, Fred Jensen wrote:
> The K3 has isolation transformers on LINE IN/OUT.  You don't need to
> add any more.

And THOSE transformers are unnecessary -- all that is needed is proper
BONDING.

> I assume you're using the term "ground-loop problems" in the generic
> [and somewhat archaic] sense.

Yes. Indeed, there is no such thing as a "ground loop" -- it's an
entirely false concept.

> Make sure that you're not using the shield of any of the cables [RF or
> AF] as the bond between your component's chassis' or enclosures.

Right. That is NOT a bond. Indeed, part of the CAUSE of these hum/buzz
problems is that the cable shield is NOT connected to the chassis at one
or both ends.

> They should all be directly bonded together.  If isolating the shields
> with external isolation transformers fixes the noise, that's a huge clue.

73, Jim K9YC


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[Edward R Cole]

I bought an ac line isolation transformer for my workbench at work
some years ago.  The building had a horrendous ac line noise and
ground faults which mgmt was not willing to pay to correct, so this
got the test equipment grounds isolated to avoid discharges into open
ckts when using test probes or solder iron.  Certainly not an ideal situation.

You should not use this solution at home (dangerous).  Fix your
grounding system, instead.

Re: antistatic pads: best to use one in doubt.  But I would not
connect anything to the green wire system.  I have antistatic solder
station so know its safe, and always work on unpowered ckts -
disconnected equipment wiring from PS.

That being said I have done considerable repair and assembly without
a pad but using just a wrist strap.  Sometimes not even that.  I've
gotten to know which devices one does not risk and those that appear
more durable.  But I keep the devices in their antistatic bags until
they are installed.  I touch my tools to chassis ground before
picking the device up and immediately place the device into position
for soldering - minimize handling, if possible.  RF power devices
"seem" more durable than small-signal devices (but they are more
expensive).  Always use antistatic pad/straps when installing preamp devices.

I detest synthetic clothes so that is not an issue -cotton for
me.  Be careful of wool clothing.  I'm also lucky because our climate
is usually humid.  Only in deep winter extreme cold will lower
humidity to levels where you draw sparks from everything you touch -
not a good time to build anything.  But if you sit down use
antistatic devices and not get up walking around during your
sensitive work it should be OK.  Best advice is to limit the duration
of exposure for the device - beating the odds.

73, Ed - KL7UW
http://www.kl7uw.com
     "Kits made by KL7UW"
Dubus Mag business:
     [hidden email]

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