Ground loops?

Discussion in 'General Electronics Chat' started by MikeD_72, Dec 25, 2008.

  1. MikeD_72

    Thread Starter Active Member

    Nov 11, 2008
    Hi all,
    I have developed a simple spectrum analyzer circuit that is powered by a wall transformer. It receives audio input and outputs a handful of frequencies to LEDs. I am using a "Y" adapter at the audio input so that I can listen to the audio with headphones while the circuit is operating.

    I'd like to improve this project by introducing some powered electronics. The first of these is to setup powered speakers instead of headphones. Second is to use a stereo or computer's audio as the signal, instead of a battery-powered mp3 player. Later, I may also decide to go for higher-power LEDs.

    My question has to do with ground loops. By hooking up these power electronics into my circuit, is there a chance I might create a ground loop and damage my equipment? How can I design my circuit improvements so that I do not have to worry about damaging my circuit or audio equipment?

    Last edited: Dec 25, 2008
  2. dha

    New Member

    Dec 25, 2008
    Mike, you need to explain the problem in more detail. For example, why are you listening with headphones at the input? Seems you would listen at the output, right? Also, why are you connecting LED's to the output? Is this just to get an indication that you have output?
  3. MikeD_72

    Thread Starter Active Member

    Nov 11, 2008
    Ah, sorry, graphic equalizer is not the correct term. I've built a spectrum analyzer that filters various frequencies and outputs the resulting magnitudes to LEDs. I'm not listening to the filtered output, I'm listening to the input. Hope that helps clear things up.
  4. mik3

    Senior Member

    Feb 4, 2008
    You can use a set of PC speakers instead of the headphones. PC speakers have a built-in amplifier, so you don't need to build an amplifier. It will be ok to connect them because the wall transformer is not grounded.
  5. MikeD_72

    Thread Starter Active Member

    Nov 11, 2008
    Right, I think that makes sense. Basically, because I have a transformer at the wall to power my circuit, the circuit ground is floating.

    I guess the same principle applies to my audio input. Since my laptop either A) runs off a transformer or B) runs off of battery power, I can use it as the audio signal into my circuit.

    So to make sure I've learned my lesson here:
    1) Using a transformer provides isolation from one circuit to another
    2) Using a transformer to power the circuit creates a floating ground


    I suppose there's one more thing - is the typical line level output of a computer or stereo equipment different from that of an mp3 player? I imagine not because the volume can be matched between all 3 devices when listening with headphones.