new PC powersupply adds speaker noise!?

[NOP]

Hi gang,

In my MAME machine, my ATX power supply burnt up so I had to replace it.  The new supply is a different vendor than the old one, but the output wattage is the same and it has roughly the same amount of connectors available on it.

Anyway, after hooking it all up, I'm now getting a lot of interferance noise over my sound system.  It isn't terrible, but there's a constant hum over the speakers (which sounds like fan) and I can now hear the hard drive being accessed over the speakers.

Aside from changing the ATX power supply, nothing else in my configuration has changed, including the way I've got it wired.

Not being much of an electronics geek, can I clean this up by grounding something or adding a small capacitor to one of the signals or something like that?

My sound system is simply a cheapo pair of PC speakers which were originally powered with a 12v wall wart. I've since hardwired it directly to the 12v line on the power supply so it powers up when the PC does.

thanks for any possible suggestions...

-jeff!

[DrewKaree]

Not sure if a line condiitioner would work in this case, but that's what's normally used to solve this problem.  It's basically a little isolation module.  I haven't ever used one in an application like this, though, so I don't know how you'd go about working it in there.  

Another thing to check - are any of the other molex connectors touching anything/each other?  I DID have a similar problem that was caused by two molex connectors touching and then touching something else...separating them and tying them off solved it, but my situation was different than yours (different wattage replacement, 2 additional molex connectors, added a fan) so I can't say with certainty that this is your specific problem.  

Also, I'm no electronics expert, but I recall reading in a phono manual about this problem, and they called it a "ground loop" issue that required a grounding strap or plugging the unit into a properly grounded outlet.  

Take all that for what it's worth.  Hope it helps or someone jumps in to tell you I'm an idiot and "THIS is what the problem REALLY is".  Good luck.

[krick]

I found this dc power supply noise filter circuit in a book I have called "Do-it-yourself Projects for Guitarists" by Craig Anderton.  He recommends adding this circuit to any power bricks that are adding hum to an audio circuit.  I think the concept will still apply to the way you have them hooked up.





That being said, you might want to question the quality of your power supply.  There are some unbelievably crappily made power supplies on the market.

I had a system that I swore had a defective hard drive.  It turned out to be a weak power supply that wasn't able to keep proper voltage levels during heavy drive activity.

Fortron FSP power supplies are well made, low priced units.
They are also sold under the Verax name.  Verax is Fortron's distributor.

Check out these articles at Tom's Hardware where he talks about them...
http://www6.tomshardware.com/howto/20021021/index.html
http://www6.tomshardware.com/howto/20040122/index.html

I wholeheartedly recommend this model...
Fortron 300W FSP300-60ATV ATX P4
http://store.yahoo.com/directron/fsp30060atv.html
For $27, you can't go wrong.

I have one in each of the three computers in my house.

Quiet, powerful, rock solid, AND cheap.  What more could you ask for?


Finally, if you can't solve your problem, you might want to consider getting a set of PC speakers that is powered off of a USB port (no power brick).  That's what I have in my cab.

Here's a thread that follows what I went through with my speakers...
http://www.arcadecontrols.org/yabbse/index.php?board=1;action=display;threadid=16381

I ended up buying 12 pairs of the USB speakers in bulk because the price was right.  I've been slowly selling the extras off on eBay...
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=4127303025

[AlanS17]

You may want to check for other more obvious and easier to solve problems. Make sure your speaker wiring hasn't fallen closer to the new components.

Also, the problem may be in the sound card and not the line. If it's a PCI card, try moving it to a PCI slot further away from the other components.