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 Post subject: Power switching question
PostPosted: Sep Fri 25, 2020 11:49 am 
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I have a computer and stereo in my 12' X 12' building and I want it to turn the stereo on and off as the computer turns on and off.

I can use one of those current sensing plug in things like I have on my main stereo int he house, but the pro audio sound card in the computer produces a noise when the computer turns off and the voltage to the OP-AMPs on the board ramps down. The current sensing plug doesn't turn off quick enough.

Would it be possible to for instance use a 12 volt automotive type relay I could connect to a source of +12 volts in the computer?

Or is there a better way to do it or is there something I can do to the sound card to where that brief noise isn't present at turn off?

In a way I'm a bit concerned about using a regular automotive relay as that is putting 120vac close to +12 Vdc and if the relay were to fail just right it could put 120vac on the 12 volt line. perhaps a solid state relay would be better in this instance.


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 Post subject: Re: Power switching question
PostPosted: Sep Fri 25, 2020 3:30 pm 
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Not sure what you mean by "automotive type" relay. There are numerous styles of 12 volt relays with contacts designed to withstand 120 volts and higher without problems. Here is just one example:

Image

https://www.todaycomponents.com/omron-l ... gJBfvD_BwE

How long does your amp continue to operate after the power is switched off? Some continue for several seconds while the caps discharge after power is removed. In this case, you would need to remove the audio feed as well.

Dave


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 Post subject: Re: Power switching question
PostPosted: Sep Fri 25, 2020 3:54 pm 
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There's an active crossover before it which seems to shut off fairly quickly.

Plus the amp I think has a dc protection relay so it shuts the speakeds off quick.


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 Post subject: Re: Power switching question
PostPosted: Sep Fri 25, 2020 11:58 pm 
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You might do it completely in the operating system with no extra parts.

Go to device manager and identify the sound card. Disable it. Turn off your computer and see if it makes the sound.

If if doesn't make the sound, then write a batch file that turns off the sound card before the computer shuts down.


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 Post subject: Re: Power switching question
PostPosted: Sep Sat 26, 2020 12:02 am 
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Think it has to do with the DC voltage.

I have a two way active crissovwr I built that does the same when the power supplly voltage drops below a certain point


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 Post subject: Re: Power switching question
PostPosted: Sep Sat 26, 2020 4:59 am 
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Macrohenry wrote:
You might do it completely in the operating system with no extra parts.

Go to device manager and identify the sound card. Disable it. Turn off your computer and see if it makes the sound.

If if doesn't make the sound, then write a batch file that turns off the sound card before the computer shuts down.


So did you try this? It's easy enough. Let us know.


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 Post subject: Re: Power switching question
PostPosted: Sep Sat 26, 2020 6:09 am 
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But will disabling the sound card remove the DC voltage from the card?

The issue based on previous experience with certain OP-AMPs is that when the DC voltage gets below a certain point some can produce a spike of noise.


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 Post subject: Re: Power switching question
PostPosted: Sep Sat 26, 2020 5:06 pm 
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Tube Radio wrote:
But will disabling the sound card remove the DC voltage from the card?

How can you know until you try it? It's easy and you stand gain either a fix or knowledge, and you lose nothing.

Getting straight to the point, the question is do you want to get rid of the sound or do you want to remove the DC voltage from the card?

Your complaint was the unwanted sound, not the DC voltage per se. Removing the DC Voltage is just one way of solving the problem. Maybe there's an easier, quicker way, which is to disable the board so the DC voltage drops off internally before you ever turn off the computer. Whether or not it actually drops of, I would still expect the board not to pass sound when disabled.

It's easy enough to see if it works. Just try it. No harm done and it just might solve your problem.

Start>Computer>Device Manger>Sound, Video and Game Controllers>(Your Pro Sound Board)>Disable
Then turn off computer and see if you hear the sound.

You can also type "Device Manager" in the Start search box.

And let us know if it works!


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 Post subject: Re: Power switching question
PostPosted: Sep Sat 26, 2020 5:34 pm 
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The issue is this.

When the dc voltage is removed from the card when the computer powers off it produces a nasty spike of noise.

Thats the same thing my two way active crossovsr did and it happened when the +/- supplies dropped to about 3 Vdc once the crossover was turned off

I can try what was suggested but based on my experience it may mot have the desired result.


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 Post subject: Re: Power switching question
PostPosted: Sep Sun 27, 2020 5:55 pm 
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Tube Radio wrote:

I can try what was suggested but based on my experience it may mot have the desired result.


Results? Inquiring wants to know. I'd try it myself, but my audio is on the motherboard.


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 Post subject: Re: Power switching question
PostPosted: Sep Mon 28, 2020 12:24 am 
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Either later tonight I'll connect a scope up to one of the sound card outputs and record a video of it when the computer powers off so the noise spike can be seen.

I'll also try disabling the sound card and see what happens.

EDIT:

Thinking about it when I had the card in my windows xp pc I dont think I had this issue at all with the stereo i had in use at the time about 5 years ago.

So it's either how the voltage on the mothrtboard drops at power off or its how the power supply voltage drops at power off.


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 Post subject: Re: Power switching question
PostPosted: Sep Wed 30, 2020 8:24 pm 
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So when the computer powers off I get this on the output of the soundcard.

Attachment:
1 waveform.jpg
1 waveform.jpg [ 283.49 KiB | Viewed 229 times ]


I took a video and uploaded to photobucket since they just brought back their video uploading and playback, but for some reason the video doesn't play so I just took a picture.


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 Post subject: Re: Power switching question
PostPosted: Oct Fri 02, 2020 4:11 am 
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What happens when you disable the sound card before powering off the computer?


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 Post subject: Re: Power switching question
PostPosted: Oct Fri 02, 2020 10:56 am 
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Same thing as disabling the card doesn't remove the power supply voltage from the card.

Unfortunately I can't power up the XP machine the card came from otherwise I'd try it in that computer to see if it does the same thing.

However I can try the power supply from that computer and see if it causes the same issue, although I have to remove the motherboard power plug and wire it in to the other supply given the motherboard connector is 10 pins and the other supply uses a 20 pin connector.


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 Post subject: Re: Power switching question
PostPosted: Oct Fri 02, 2020 6:29 pm 
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Thanks. To confirm, you performed that test and it definitively proves that when the card is disabled, the card still passes audio to the output, correct?


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 Post subject: Re: Power switching question
PostPosted: Oct Fri 02, 2020 6:43 pm 
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It doesn't pass audio from the computer as the card is disabled, but it does still cause that noise when I turn the computer off given the power supply voltages are still applied to the PCI slot the card is plugged into.


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 Post subject: Re: Power switching question
PostPosted: Oct Mon 05, 2020 9:59 pm 
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The video finally showed up properly.

Basically this is what happens when the computer turns off when it is shut down.

Image

EDIT:

It was the computer's power supply.

I wired up a 500 watt computer power supply from a 2007 PC and the weird waveforms are gone. Only a slight variance in DC level upon power off which only produces a slight low level thump in the speakers which is fine.


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