eliminating power "whine" from AC plug - diyAudio
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Old 28th December 2012, 02:38 AM   #1
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Default eliminating power "whine" from AC plug

not sure if this is the right forum catagory but wasnt sure where to ask my question......but like the title says im trying to eliminate a whine in an amp that occurs as soon as u plug the unit in and turn it on...even if the volume is all the way down....this is the item in question.... Amazon.com: Sondpex Active Speaker System & Digital Music Player: Electronics

i realize its a very low end product but i figured you guys might be able to help me eliminate the noise im getting...i havent tried DC power input (i use it at work) but plugging it into the wall definitely causes whining....didnt know if there was something i could modify or add to eliminate this....if pics of the guts are needed just let me know and i can get some.

*edit** i get the whine from all sources....whether it be the fm tuner or the sd card reader or the aux jack

Last edited by pantstain; 28th December 2012 at 02:41 AM.
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Old 28th December 2012, 02:53 AM   #2
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The unit probably isn't designed especially well to prevent noise from the AC input, eg a poor quality internal SMPS. The easiest thing to do IMO would be to get a decent regulated 12VDC supply that you can plug into the wall. Something in the 3-5 amp range should do it, as the output is surely closer to 20W than 200W.
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Old 28th December 2012, 03:02 AM   #3
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definitely closer to 20w. nowhere near 200w lol. i knew that going in though i heard it from a friend before i bought it. i suppose a pc power supply would work but thats kinda big and bulky.....hmmmm. is it possible to build one for a decent price? (very new to DIY audio)

**edit** btw fuse in the side is only a 1 amp quickblow fuse
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Old 28th December 2012, 03:07 AM   #4
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Does the power supply brick have any ratings marked on it? That would be a guide to getting another. It's 12v volt, right? Does it say how many amps or milliamps?
You can often find these surplus for cheap. That's what I do.
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Old 28th December 2012, 03:37 AM   #5
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Not cost-effective unless you have a switchmode ps laying around (I'd stay away from pc types), or already have a transformer for a linear ps. Personally I'd choose a linear ps and search for a discounted transformer or open-frame supply.
You could try an off-the-shelf SMPS such as this 12V 4A SMPS since these are so common nowadays.
There is this 12V 4A linear supply that looks to be the same as the one offered here on ebay. Neither site shows the unloaded output voltage, but it wouldn't be too difficult to add a regulator and case, if you wanted to do some DIY.

Pano asks a good question, so I'll repeat it. Does the unit or manual list the power requirements for the DC input?
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Last edited by sofaspud; 28th December 2012 at 03:40 AM.
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Old 29th December 2012, 03:39 PM   #6
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At work. Will try to get time to check when I get home
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Old 5th January 2013, 02:20 AM   #7
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heres a couple pics of inside
Attached Images
File Type: jpg 20130104_195952.jpg (667.4 KB, 62 views)
File Type: jpg 20130104_195928.jpg (399.7 KB, 62 views)
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Old 5th January 2013, 03:34 AM   #8
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Couldn't find reqs for dc input (other than what's listed as an output on the transformer)
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Old 5th January 2013, 06:50 AM   #9
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That transformer is only 12V @ 1.5A. Either the SMPS or linear supply I linked to would work fine. Or something similar you can find for the right price.
Then you could run your active speaker from the DC input, and if you wanted to, remove that transformer for use in some other DIY project.
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Old 5th January 2013, 10:03 PM   #10
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And that will eliminate the noise? Alright tyvm for the help!
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