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pantstain 28th December 2012 01:38 AM

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.... 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

sofaspud 28th December 2012 01:53 AM

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.

pantstain 28th December 2012 02:02 AM

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

Pano 28th December 2012 02:07 AM

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.

sofaspud 28th December 2012 02:37 AM

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?

pantstain 29th December 2012 02:39 PM

At work. Will try to get time to check when I get home

pantstain 5th January 2013 01:20 AM

2 Attachment(s)
heres a couple pics of inside

pantstain 5th January 2013 02:34 AM

Couldn't find reqs for dc input (other than what's listed as an output on the transformer)

sofaspud 5th January 2013 05:50 AM

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.

pantstain 5th January 2013 09:03 PM

And that will eliminate the noise? Alright tyvm for the help!

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