audio buzzing after PC is turned off

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

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).

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.

OK. That would be a circa 2002 M-Audio Audiophile 2496 PCI card:

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?

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

Do you have a ground loop isolation audio transformer handy? Something like one of these[1]? 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.

Velcom bag Yeff!

RL

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.

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

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

Have you considered learning Newspeak, Speedtalk or Klingon, instead? 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.

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.

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.

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

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.

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.