audio buzzing after PC is turned off

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Pretty simple set up.  I have my phono output from my desktop Audiofile  
2496 sound card driving an Altec Lansing speaker set.  Works fine when  
everything is on, but when the desktop is turned off I am getting a  
buzz/ hum from the speakers and loud enough that I power them off.  Why  
is this and how to remedy?  Thanks.

Re: audio buzzing after PC is turned off

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I think your desk-top has a soft and a hard power switch. There  
may also be other peripherals that are still running plugged  
into the desktop.

If the humming is still there when the hard power switch is off,
try terminating the signal lines from the PC with 600R.  
The PC may go high-Z when turned off - becoming a hum antenna.

Fool with cables to see if any movement modulates the amplitude.  

Check grounding on the PA -  are these active loudpeakers?

The source volume should be high, the amplifier's gain low, for  
best S/N performance.

RL

Re: audio buzzing after PC is turned off
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When the PC is powered on, there's DC power going to the sound-card
output circuitry.  The output amplifiers (when powered on) should have
a relatively low output impedance - typically a couple of hundred ohms
for a "line level" output, quite possibly less.  Since the speaker
set's input circuitry has a high impedance (at a guess, 47k ohms or
higher), the voltage on the signal conductor will be dominated by the
output amplifier - and when you aren't playing music, it'll be right
about at zero volts ("dead silence").

When you power off the computer, the sound card loses power and its
output amplifiers shut down... they go to a "high impedance"
open-circuit state.  At this point, the sound card isn't holding the
signal line at zero volts.  Instead, the signal line will start acting
like a simple antenna, picking up 60-cycle buzz and hum from magnetic
and electrical fields around the PC.  With its high input impedance,
the speaker set will be sensitive to even small noise currents and it
will amplify the resulting voltage.

If you were to unplug the cable from the PC, and touch the end of the
plug with your finger, you'd get a similar (possibly much-louder) buzz.

If this really bothers you, you can probably make a "noise stopper"
device, wired between the sound-card output and speaker set.  You
would need a small (sensitive-coil) 5-volt-DC double pole,
double-throw relay.  The relay coil would be wired to a USB plug which
would go into the PC, so that the relay would be energized when the PC
was turned on.  You would wire one set of the normally-closed relay
contacts, and a 47-ohm resistor, across each of the two audio signal
lines and audio ground.

When the PC is off, the relay would be in its normally-closed
position, connecting the 47-ohm relay across the audio signal.  This
would silence the audio, muting the buzz.

When the PC is on, the relay would operate, opening the
normally-closed contacts, disconnecting the resistors and unmuting the
audio.

A similar unmute-upon-power-on system is used in many commercial audio
components (e.g. tuners and preamps).

Re: audio buzzing after PC is turned off
On Sunday, June 13, 2021 at 6:23:58 AM UTC-7, W Pulaska wrote:
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Buzz means harmonics from a sawtooth, typically.   That indicates that the
speaker power source (a wall-wart power brick??) has a capacitor that has
gone high-impedance (high ESR, for instance).   Speaker  amplifiers aren't
critically dependent on exact-match power bricks, you can find another
(if necessary splice the cord from the old one to fit the socket) that'll work.

Sometimes, you can open and repair a power brick.   Not often.

Re: audio buzzing after PC is turned off

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OK.  That would be a circa 2002 M-Audio Audiophile 2496 PCI card:
<https://www.newegg.com/m-audio-audiophile-2496/p/N82E16829121120>

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One speaker or both speakers?

Is the buzz/hum still there when you turn off the unspecified model
Altec Lansing (amplified) speakers?  I'm wondering if the problem is
in the computah or in the amplified speakers?

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Instead of turning off your unspecified model PC, try unplugging the
AC power cable from the PC to insure that it's really turned off.  If
the hum/buzz disappears, my guess(tm) is the WoL (wake-on-LAN) power
from the power supply is making its way somehow to the sound card.
I've fixed one similar "noisy when turned off" PC problem by replacing
the power supply.  Unfortunately, I didn't bother trying to figure out
the exact cause.

Does your unspecified model PC also have a built in sound card on the
motherboard?  If yes, unplug the 2496, and try running your
unspecified model Altec Lansing speakers from the motherboard sound
(green) output.  If the hum/buzz goes away with motherboard sound,
then the problem might be something on the M-Audio 2496 card.  To be
sure, try installing a different PCI sound card.  If the replacement
PCI card doesn't buzz, then it's probably something on the M-Audio
2496 card.

Do you have a ground loop isolation audio transformer handy? Something
like one of these[1]?
<https://www.amazon.com/s?k=ground+loop+isolator+3.5mm>
<https://www.ebay.com/sch/i.html?_nkw=ground+loop+noise+isolator+3.5mm
I'm not sure what it might mean if installing one of these fixes the
hum/buzz problem, but it would be an interesting test.

Good luck.


[1] I carry some of these in my toolbox.  They mostly get used to
break the audio ground loop between the TV earphone jack and amplified
speakers.


--  
Jeff Liebermann                 snipped-for-privacy@cruzio.com
PO Box 272      http://www.LearnByDestroying.com
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Re: audio buzzing after PC is turned off
wrote:

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Velcom bag Yeff!

RL

Re: audio buzzing after PC is turned off

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Hopefully, you don't talk like that.  Thanks.  The only problem is
that I didn't go anywhere.  I spent much of my spare time in
rec.bicycles.tech discussing arguing except bicycles and technology. I
recently decided that a change would be nice and tried to answer a few
questions in other groups.  So far, I haven't lost my ability to
mangle my answers, which I demonstrates that I haven't completely
degenerated.  Around October 2020, I closed the office and moved
everything to my house.  I'm now living in a cardboard box jungle. I'm
still doing computah repairs working out of my Subaru.  It's an
interesting experience driving around in a nearly empty car, and
having to carry everything I might need for a service call down 50
stairs, throw the boxes into the Subaru, do the rap air, haul the
stuff back up the 50 stairs, and replace the contents to their former
hiding places.  I should probably retire, this time for real.


--  
Jeff Liebermann                 snipped-for-privacy@cruzio.com
PO Box 272      http://www.LearnByDestroying.com
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Re: audio buzzing after PC is turned off
wrote:

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I figure my 'retirement' costs about $10K a year - to keep working  
and house 500sq feet of lab and storage. Under-achievment at it's  
finest.

Seeing as any kind of potentially humorous attempt at dialect is  
considerd as cultural theft, I'b develobing by owd web slang, widg  
iz basigly stuufed node togging.

RL

Re: audio buzzing after PC is turned off

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Have you considered learning Newspeak, Speedtalk or Klingon, instead?
<https://en.wikipedia.org/wiki/Newspeak
<https://en.wikipedia.org/wiki/Speedtalk
<https://en.wikipedia.org/wiki/Klingon_language
There are also a large number of dead languages which were popular in
their day.  They could be modernized (like Hebrew).  However, web
slang seems to have a rather short lifetime.  Idioms and phrases that
were popular when I was learning computers have all but disappeared,
to be replaced by incomprehensible gibberish of unknown origin,
similar to what you're proposing.  Also, your proposed web slang
language is lacking a key component required for any technical
discussion.  It lacks acronyms, which are the foundation of today's
technobabble.

--  
Jeff Liebermann                 snipped-for-privacy@cruzio.com
PO Box 272      http://www.LearnByDestroying.com
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Re: audio buzzing after PC is turned off
On Wed, 16 Jun 2021 21:59:44 -0700, Jeff Liebermann wrote:

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   Just wait 'til you forget what stuff is in which box!

Re: audio buzzing after PC is turned off
wrote:

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No need to wait.  It's been driving me insane for eight months.  I'll
spare you the details, but I had to leave in a hurry.  There was no
time to properly gift wrap everything, buy proper bankers boxes, or
even label things.  I did my best to put similar things in separate
boxes, but even gave up doing that.  Worse, I didn't have time to much
triage on the junk.  So, I tossed, donated, sold, or gave away what I
could, and hauled most everything to the house.  (Note:  I don't have
a garage).  I now have several mountains of boxes.  Finding anything
usually results in something resembling an archeological dig.  This
morning, I was trying to find an XP Home CD.  It was easier to
download an ISO image than to find the CD.  I'm slowly going through
the mess and re-sorting everything, but will take months (if not
years).

Gotta run.  Going to the big city (Santa Cruz) to get a replacement
drive shaft for the Subaru.  There went my stimulus money.



--  
Jeff Liebermann                 snipped-for-privacy@cruzio.com
PO Box 272      http://www.LearnByDestroying.com
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Re: audio buzzing after PC is turned off
On 18/6/21 2:48 am, Jeff Liebermann wrote:
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Catalog, don't sort. Open one box a day,, write down what's in it, then  
label and close it up again. Soon you'll have a file you can search to  
tell you which box to find stuff in.

Glad to see you back and in fine fettle, Jeff!

CH.


Re: audio buzzing after PC is turned off
On Fri, 18 Jun 2021 09:33:25 +1000, Clifford Heath

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I didn't have time to itemize or classify everything.  My temporary
fix was to dump the contents of the smaller boxes on the floor, take a
digital photo, print the photo, paste it to the box, and put
everything back into the box.  That didn't work because it was
difficult to see clearly all the items when scattered.  So, I switched
back to numbering the boxes and itemizing the contents.  That works,
but takes forever, especially when I want to move things from one box
to another.  The boxes are also not of uniform size and frequently get
moved around the house.  The result is I sometimes know which box has
the goodies, but can't find it under the pile of boxes.  I'm not quite
ready for RFID tags, but I'm tempted.  I'm going to need to clear out
at least one room, so I have a place to do the sorting.  I'm also
going to need to downsize the pile.  At this time, I'm working on a
rather large pile of cables and wire, which are probably going to the
recyclers.

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Thanks, but don't assume that I'm back.  Now that I'm retired, I'm
more busy than when I was working.  Besides people wanting a piece of
my non-existent spare time, I'm still cleaning up from last summer's
fires and a storm in December which knocked down a few trees.  If I'm
on the computer posting drivel to Usenet, it's because I'm too tired
to do anything else.

--  
Jeff Liebermann                 snipped-for-privacy@cruzio.com
PO Box 272      http://www.LearnByDestroying.com
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Re: audio buzzing after PC is turned off
wrote:

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Moving every 3-4yrs for projects, I kept the shipping containers and  
tended to store stuff in shipable hardware - even leaving stuff in  
labelled boxes between moves.

Still not obvious where a specific item might have been sorted,  
but cuts down on the possibilities.

Things will always go missing. When I accidentally find them,  
they go back to where I think they should have been.

I've got a pretty good idea if some things are going to be more  
useful than others in the near future - grading their accessibility.

Hardest stuff is project-specific. Was it stored as project stuff  
or general use? Connector or harnesse? Mech hardware or specialized  
conductor/insulator? Flat or vertical? Office or lab? Which SW rev  
on which machine?

Some test or fab configurations of hardware and software, you can  
never get back - too many immediate and unrecordable practical  
quirks.

RL

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