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50Hz Hum problem

Discussion in 'Recording' started by GentleG, Feb 8, 2003.

  1. GentleG

    GentleG Guest

    Hi

    I hope someone can help me with this.

    The problem is: I'm having a lot of 50Hz in my audio signal.

    I'm running my DAW using a tascam us-428 soundcard.
    I connect some gear (doesn't matter what, let's say a synth) to the us428
    I get a lot of 50 Hz (and harmonics)
    Everything is on the same AC outlet
    This dissappears completely when I disconnect the synth from the us428 (unplugging the audiocables)
    Or, when I disconnect the synth from my AC outlet

    So this definately is a power issue

    Another thing:
    There is a big difference between switching the synth on and off

    Funny thing is I get more 50Hz when the synth is off

    you can have a look at this text and some FFT pictures at http://www.goltstein.com/help/

    Thanks
     
  2. Ethan Winer

    Ethan Winer Active Member

    G,

    > Everything is on the same AC outlet ... This dissappears completely when I disconnect the synth from the us428 <

    This is surely caused by a ground loop.

    > Funny thing is I get more 50Hz when the synth is off <

    That's not really so surprising.

    The short answer is that an audio isolation transformer will solve this. You can pay a lot or a little for these, with more money buying better transformers having less distortion and a better frequency response.

    One inexpensive solution is the Ebtech Hum Eliminator. You say 50 Hz. so I assume you're not in the US. I don't know if Ebtech is available outside the US but it probably is. Or you may be able to find an equivalent where you are.

    --Ethan
     
  3. Kurt Foster

    Kurt Foster Distinguished Member

    Try an experiment. Use a "ground lift" on the synth. If this eliminates the hum it's a good chance the synth is wired out of phase. At any rate you’re not in any danger by lifting the ground on the synth. If a lift solves the problem go ahead and use it that way. Fats
    ------------------------------------------------------------------------
    Tannoy, Dynaudio, Blue Sky, JBL, Earthworks, Westlake, NS 10's :D , Genelec, Hafler, KRK, and PMC
    Those are good. …………………….. Pick one.
    ------------------------------------------------------------------------
     
  4. GentleG

    GentleG Guest

    Hi

    Thank you both for your reply

    The problem does not go away with lifting the ground of the synth.

    I've just been looking for 'audio isolation transformer' on google.
    I'm not sure what I'm looking for,
    I guess it's a little device I put somewhere in the audiosignal between the synth and my us428?

    O and yes, I live in the Netherlands (240V 50Hz)

    Cheers
     
  5. realdynamix

    realdynamix Well-Known Member

    Just a question G, have you turned off the computer's monitor while the CPU and Synth is still hooked up and running?

    As per Ethan,
    http://www.ebtechaudio.com

    --Rick
     
  6. GentleG

    GentleG Guest

    Hi Rick

    Turning the comp monitors on or off doesn't matter

    Thanks
     
  7. stat1k

    stat1k Guest

    Hey dawg,

    Do you have everything in the same outlet, like say on a power bar? Or in seprate outlets?

    lemme know.

    jaret
     
  8. GentleG

    GentleG Guest

    Hi

    Same outlet

    Thanks
     
  9. Kurt Foster

    Kurt Foster Distinguished Member

    OK I'll take one more stab at this... has the power cord to the synth ever been modified or repaired? This sounds like the cold and hot sides may have been reversed. Try the ground lift but flip the cord over if you can. I don't know what power cords are made like in the Netherlands but if you can't tun them over try getting a new end, lop the old one off and switch the hot and cold leads around. If this doens't fix the problem then it's time to take the synth to the repair person to have it looked at ..... Kurt
     
  10. GentleG

    GentleG Guest

    Thanks again for the reply

    (Netherland: 240V AC 50 Hz)

    The problem is independent of the synth / whatever I use.

    My soundcard is a tascam us428
    so it is connected to my pc via USB
    it is powered through an ungrounded adapter, the pc is grounded

    Any gear (f.e. a synth) connected to the us428 is grounded (on the same outlet as the pc)


    New information / clues:

    the audiocable to the us428 even picks up some 50Hz when the audiocable is not connected to a synth. So it seems I've built my own 50Hz radio here (sorry, my english is not good enough to explain this technically). no harmonics of 50Hz

    When connecting this 'loose' audiocable to a synth the 50Hz signal stays the same (no increase in amplitude) but I do get all the odd harmonics of 50Hz (150, 250, 350, etc.) extra.

    My audioables are unbalanced but properly shielded (contradictio in terminis? :roll: )


    Thanks again for your time
    :c:
     

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