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Topic: OT -- Home electrical problem (27 msgs / 495 lines)
1) From: Derek Bradford
Please excuse the OT post, but I believe there are a few of you on
here who might be able to help me.  I'm having an electrical issue in
my apartment and I'm not sure where to start with it.
I'm in Korea, on 220V 60Hz.  I have a pair of Altec Lansing powered
subwoofer computer speakers, as well as a laptop (and other appliances
of course, but these are the two in question).  With the speakers on
(no music; just powered on), all is fine.  But when I plug my laptop
in, the speakers develop a low frequency hum.  It happens as soon as
my power brick is connected.  I've changed outlets, but it hasn't
helped.  For the record, most Korean apartments, mine included, have
only 3 or 4 circuits.  Mine has 3.  8 receptacles, some overhead
lights, A/C, washer & stovetop, and that's about it.  The other laptop
has no effect on the speakers; only mine.  I'm also not running most
of this stuff, so it's probably not a power draw thing.  Maybe a bad
power brick?  (At the moment I'm running only 3 lights, a rice cooker,
and 2 laptops.)
Any thoughts or suggestions?
Thanks,
--Derek
-- 
The Uglyroast 3! Coffee Roaster.  ...Now 85% less ugly!http://uglyroast.atspace.com

2) From: J.W.Bullfrog
Are the speakers being driven by the laptop, and do
you have this problem when you are on battery?
What about the other laptop?
Derek Bradford wrote:
<Snip>
-- 
There is a theory which states that if ever anyone discovers 
exactly what the Universe is for and why it is here, it will 
instantly disappear and be replaced by something even more 
bizarre and inexplicable.
There is another theory which states that this has already happened.

3) From: Derek Bradford
The speakers have their own power cord.  There is hum whether or not
they are connected to the laptop--it's purely a power thing.  As soon
as the power brick is both plugged in AND connected to my laptop, the
hum begins.  Simply plugging in the brick doesn't do it.
There is no problem when I'm on battery.
The other laptop does not cause the problem.  Unfortunately the power
bricks are incompatible, so I can't switch them to rule out my actual
laptop.
On 7/17/06, J.W.Bullfrog  wrote:
<Snip>
-- 
The Uglyroast 3! Coffee Roaster.  ...Now 85% less ugly!http://uglyroast.atspace.com

4) From: David Liguori
There are several possibilities, but one of them is magnetic field radiation from the power brick getting into the electronics of the speaker system.  I assume those electronics are located in the subwoofer box.  Try changing the relative distance or orientation of the power brick and subwoofer.
J.W.Bullfrog wrote:
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5) From: Derek Bradford
I will.  Hang on...
On 7/17/06, David Liguori  wrote:
<Snip>
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The Uglyroast 3! Coffee Roaster.  ...Now 85% less ugly!http://uglyroast.atspace.com

6) From: Derek Bradford
Seems I didn't quite do my homework properly.  It seems the speakers
must also be plugged into the laptop (audio out), which I hadn't
noticed before.  Distance doesn't seem to have an impact, though.
On 7/17/06, Derek Bradford  wrote:
<Snip>
-- 
The Uglyroast 3! Coffee Roaster.  ...Now 85% less ugly!http://uglyroast.atspace.com

7) From: J.W.Bullfrog
Derek Bradford wrote:
<Snip>
has this just started? Maybe a failure in some sorta filtering circuit 
somewhere in the system (not necessarily the power brick).
<Snip>
-- 
There is a theory which states that if ever anyone discovers 
exactly what the Universe is for and why it is here, it will 
instantly disappear and be replaced by something even more 
bizarre and inexplicable.
There is another theory which states that this has already happened.

8) From: Derek Bradford
It's been there since I moved back to Korea.  Unfortunately, it's a
new apartment with a new laptop.  I had the speakers last year and
they were fine.
On 7/17/06, J.W.Bullfrog  wrote:
<Snip>
-- 
The Uglyroast 3! Coffee Roaster.  ...Now 85% less ugly!http://uglyroast.atspace.com

9) From: Bill Cutts
My first guess would be a ground loop problem. If you google "ground
loop" you'll find lots of references on ground loops, what causes
them, how to try and fix them, etc. I don't know anything about Korean
power so I can't help much. The easiest way to diagnose this in a US
system is to "float" the safety ground (for instance plug three prong
plugs into a three-two adapter without connecting the dangling ground
cord) and see if that fixes the problem. Whether or not you want to do
that long term is a safety issue I won't address.
On 7/17/06, Derek Bradford  wrote:
<Snip>

10) From: Derek Bradford
Great...thanks for the advice.  I'll see what I can do.
If you're interested, Korean plugs look like this.  I actually quite
like them...they've got a solid connection, are standard and
non-polarized, and never get bent if you step on one.http://www.yung-li.com.tw/EN/products/plug_cat_g.htm#yp-22kCheers,
--Derek
On 7/17/06, Bill Cutts  wrote:
<Snip>
-- 
The Uglyroast 3! Coffee Roaster.  ...Now 85% less ugly!http://uglyroast.atspace.com

11) From: Derek Bradford
I should edit my last post for clarity.  One thing that makes the
plugs so nice is that they sink into the receptacle all the way to the
chord, not just the prongs.
On 7/17/06, Derek Bradford  wrote:
<Snip>
-- 
The Uglyroast 3! Coffee Roaster.  ...Now 85% less ugly!http://uglyroast.atspace.com

12) From: J.W.Bullfrog
I like Bills' idea.
Ben
Bill Cutts wrote:
<Snip>
-- 
There is a theory which states that if ever anyone discovers 
exactly what the Universe is for and why it is here, it will 
instantly disappear and be replaced by something even more 
bizarre and inexplicable.
There is another theory which states that this has already happened.

13) From: Mike Chester
Are the speakers connected to that computer?  If so, it sounds like you have 
a filter problem in the power supply for the computer.  The incoming AC is 
changed to pulsating DC and then filtered to a more pure DC normally, but if 
the filter circuit stops working, you get pulsating DC.  This shows up in 
the sound output of the computer (or amplifier) and you can hear the 60hz. 
in the speakers.   This is not too good for the computer either.  The 
problem could be in the "brick" or inside the computer depending on where 
the filter circuit is located.  If you have access to a good "brick" that 
would be the first thing I would try.  It may not be necessary to replace 
the whole thing.  A decent tech can replace the filter circuit, but if you 
are paying for labor it might cost more than buying a new one.
Mike Chester

14) From: Michael Guterman
Derek,
Try someone like amusicdirect.com.  You may need a device to defeat the 
ground loop.  Aragon made one (still available, I think) called the 
Magic Box.  Ground loops are very common.  You may be able to defeat it 
by making sure everything is plugged into the same circuit.
Michael
J.W.Bullfrog wrote:
<Snip>

15) From: Michael Wade
Derek, what brand is the problem laptop?
I've been having a similar problem with an IBM Thinkpad when using it to 
record video direct to HD from the camera via firewire (using DV Rack sw). 
If the brick is plugged into the laptop I get huge hum in the camera audio, 
whether or not the camera brick is plugged in, so it's not a ground loop.  I 
had assumed that it was line noise passing through the brick, but your 
experience sounds like it's possible that it is actually coming from the 
brick.
I meant to experiment with winding the DC lead from the brick through a 
ferrite ring to see if that would help but since I'm producing short videos 
I just ran on battery instead.  I'll see if I can find the info I dug up on 
the ferrite cores, but on this list its likely that someone else already has 
experience...
Michael Wade

16) From: Derek Bradford
Thanks Mike...  I don't have another brick I can try, but it's a Dell,
so I suppose I'll give them a call in a day or so when I have some
time.  Should be fun dealing with Dell Korea.
For everyone else, I'll post whatever happens when it does.
Cheers,
--Derek
On 7/18/06, Mike Chester  wrote:
<Snip>
-- 
The Uglyroast 3! Coffee Roaster.  ...Now 85% less ugly!http://uglyroast.atspace.com

17) From: Derek Bradford
Man, that is one dangerous site.  It's a good thing I'm not back home,
or I'd have had to do some shopping.
Thanks.  As for the Magic Box, I hope that's not my ultimate solution...
On 7/18/06, Michael Guterman  wrote:
<Snip>
-- 
The Uglyroast 3! Coffee Roaster.  ...Now 85% less ugly!http://uglyroast.atspace.com

18) From: Derek Bradford
It's a Dell, Inspiron 9400/XPS.
Thanks for clearing up the ferrite ring issue.  I've always wondered
what those were for, but never got around to finding out.  By always,
I'm talking a solid 10 years.  Thanks!
On 7/18/06, Michael Wade  wrote:
<Snip>
-- 
The Uglyroast 3! Coffee Roaster.  ...Now 85% less ugly!http://uglyroast.atspace.com

19) From: Spencer Thomas
After plugging both plugs into the same circuit, does it make any difference
if you reverse the orientation of one of the plugs?  If there is a ground
loop, you want to get the ground on the same "side" of both plugs.
On 7/17/06, Michael Guterman  wrote:
<Snip>
-- 
=Spencer in Ann Arbor
My Unitarian Jihad http://tinyurl.com/6valr)Name is:
Sibling Dagger of Mild Reason
What are you?http://homepage.mac.com/whump/ujname.html

20) From: David Liguori
Ferrite rings have nearly zero effect at 60Hz (or they would filter the AC power out altogether!)  They are meant to eliminate "common mode" radio frequency interference.
Derek Bradford wrote:
<Snip>

21) From: Barry Luterman
I had a Physics teacher who was a consultant to the US Gvt. in WWII. A 
German Messerschmitt was downed and they found a ferrite ring in a vacuum 
tube in the plane. They called him in as a consultant and he figured out 
it's use.

22) From: Aaron
Ferrite rings also work well on data cables as the 1's and 0's passing 
by can in an abstract way, be seen as like a frequency on the wire.  
Their main purpose is to reduce and / or hopefully eliminate noise on 
the line that may cause either a buzz or hum on the audio or 'staticy' 
or 'lines' in the video.
Aaron

23) From: raymanowen
Micheal, your idea of "winding the DC lead from the brick through a ferrite
ring" core will add some tiny inductance in the lead, that will attenuate
the GHz square waves and spikes flying around digital data and control
signals. The rat's nest wiring in computers makes me shudder. They never
heard of lead dress or shielded conductors.
The ferrite beads amount to an ECO "fix," or "workaround" for an engineering
assumption gone awry. When several leads pass through a ferrite bead, the
whole thing becomes an rf transformer.
Plugging your devices into a common extension or branch circuit will
eliminate any power ground loops. Careful- it's possible you could get over
300 volts peak between a couple of different chassis in the case of a couple
of failures if the earth grounds have been disabled on the plugs.
Remember, if your sub amplifiers are being fed the line level signal out of
the preamp, they're getting about a 1 volt signal pretty close to their
normal passband frequency. A tiny fraction of 220 volts at power frequency
could send the cones out of the baskets
The actual problem will be elsewhere- like the MOV/s in the power adaptor
"brick" not rated for the 220 vrms (11 vpk) of Korean or Euro power...
Cheers -RayO, aka Opa!
Customer service from Dell... Rots of Ruck-
But the ROK's LOVE coffee, so you may have some unanticipated horsepower.

24) From: Derek Bradford
<Snip>
It is so rated...fortunately.
<Snip>
Nice.  :)
-- 
The Uglyroast 3! Coffee Roaster.  ...Now 85% less ugly!http://uglyroast.atspace.com

25) From: Michael Wade
There have been a couple of responses pointing out my error in terms of 
frequency range of ferrite ring cores... Mea Culpa.  After digging up my 
notes and following through a little farther I found that different ferrite 
compounds are appropriate for different frequencies, but all in various rf 
bands.  Seems to be mostly a ham shack kind of thing.
Michael Wade

26) From: Derek Bradford
For anyone still interested, I haven't had the time to call Dell
yet...been too busy with work.  However, I have noticed something else
I hadn't noticed before: the hum gets louder when I open the lid/power
on the screen (or, conversely, gets quieter when the screen is
blank/closed).  Interesting.
On 7/22/06, Michael Wade  wrote:
<Snip>
-- 
The Uglyroast 3! Coffee Roaster.  ...Now 85% less ugly!http://uglyroast.atspace.com

27) From: M. McCandless
It sounds like bad DC filtering.
If the power supply (brick) has a DC output, then
a large capacitor in parallel with the output should remedy
the prob.
If the output is AC, then the power is rectified & filtered 
in the laptop.
If the latter is true, the laptop will need surgery.
McSparky
At 01:25 PM 7/22/2006 +0900, you wrote:
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