Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Static noise from psu

  1. May 19, 2010 #1
    Hello all.

    I'm not a regular from the forum or nothing, I've been looking for a solution for a problem with static noise in a speaker system and got to this post in the forum https://www.physicsforums.com/showthread.php?t=201439 is not what i was looking for but from what i read someone around here might be able to help me.

    I have assembled a home audio (ambient music) device into one of a pair of hi-fi speakers.
    I didn't have the original psu so i used a selectable voltage dc adapter.

    My problems are the following, the system is making a static noise with i suppose must come from the dc adapter, something to do with lack of ground or something. I suppose with some circuit addition it may be resolved.

    As you may be able to figure from the above i know very little from electronics but can solder and identify components.

    well if anyone care to give me some ideas...

    BTW nice forum and thx
  2. jcsd
  3. May 20, 2010 #2
    Maybe you can start by describing the "selectable voltage DC adapter," and the "home audio device."
  4. May 20, 2010 #3
    thanks for taking the time...

    the adapter is one of those simple black, i think it was from a router or modem, it states 230v~50Hz 150mA input and 12V---1000mA 12VA output, i can open the box and send a picture or describe the circuit it has if needed it's very simple a capacitor a condenser and little less aside from the transformer.

    the amplifier/radio is one of those you can install in a socket in the wall and have the speakers also in the walls or ceiling - www.ermax.pt/amplificadores_eramp2227.html - this is from the same brand but a newer model also i can take a picture if needed.
  5. May 20, 2010 #4


    User Avatar
    Science Advisor

    You call it "static", but are you sure it's not just 120Hz hum (or 100Hz if you are on 50Hz mains).

    Some devices are designed to have good "power supply rejection", meaning that noise or ripple on the input power supply(s) cause very little noise or ripple at the output (speakers). Other devices have poor power supply rejection and require very clean DC levels for the input power or else you get a noisy output. I assume that your device is one of the latter.

    BTW. What is it normally meant to be powered from? A 9V battery or something else?
  6. May 20, 2010 #5

    the device received power from a main unit in another room and i have no access to that anymore.

    By what you say i might have the 120Hz hum and the amplifier require very clean DC levels for the input power, can i add something to that one to make it "cleaner"?

    thanks for the patience.
  7. May 26, 2010 #6
  8. May 26, 2010 #7
    What does the static or noise sound like?
  9. May 27, 2010 #8
    a large capacitor across the output following the rectifier bridge and/or a zener diode of rated supply voltage should eliminate most of the problem.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook