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Thread: Strange PSU

  1. #1 Strange PSU 
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    I have a 24v switching psu that for some reason when hooked up to an amp makes the sound like a distorted mess like a wireless connection dropping in and out at the same time. It reads that it outputting 24v ; when i pull the plug out the music sounds normal for a couple of seconds before the power dissipates.


    It did work properly for a while, and i have tested the amp with another psu and its fine so definitely the psu.

    Any ideas would be appreciated...

    Thanks
    MRO Supply


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  3. #2  
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    Quote Originally Posted by mattmro444 View Post
    I have a 24v switching psu that for some reason when hooked up to an amp makes the sound like a distorted mess like a wireless connection dropping in and out at the same time. It reads that it outputting 24v ; when i pull the plug out the music sounds normal for a couple of seconds before the power dissipates.


    It did work properly for a while, and i have tested the amp with another psu and its fine so definitely the psu.

    Any ideas would be appreciated...

    Thanks
    MRO Supply
    Modern power supplies can generate lots of noise. Some of it is conducted, some is radiated.

    Also, many such power supplies are actually unstable unless loaded properly.

    An oscilloscope would be ideal for diagnosing your problem, but absent that, here are things to try:

    1) Add good filter capacitors at the input to your load (audio amp, in this case).

    2) Make sure that you are presenting at least the minimum load required by the supply. If you are drawing too little, add more load (e.g., a resistor in parallel with your amplifier).

    3) Add shielding between the power supply and your amplifier, in case that radiated noise is your problem.


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  4. #3  
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    Quote Originally Posted by mattmro444 View Post
    .......when i pull the plug out the music sounds normal for a couple of seconds before the power dissipates.

    Any ideas would be appreciated...

    Thanks
    MRO Supply
    TK has it nailed. It sounds OK when you pull the plug out because all the switching circuitry - that is causing the RF interference - is killed and the PSU is just supplying from its reservoir capacitors.

    If it used to work OK then obviously something has changed. You need to think what; have you wired it up differently, or used different cable runs etc.?

    Is the PSU in a metal case? If not, put it in one (allowing for airflow to dissipate heat production) and make sure that case is earthed.

    A simple filter on the PSU 24V output consisting of a parallel capacitor and a series inductor should help if the interference is not airborne but on the supply cables. (Add some low value parallel C's after the inductor to preserve low power supply impedance at audio frequencies).

    OB
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