Mains hum in small mixer

Discussion in 'Miscellaneous [BG]' started by instrumentalist, May 19, 2019.


  1. I have this small mixer I use to play bass late at night with headphones. (My amp has no headphone output.) Also want to use it for recording. It produces a permanent mains hum, which in this country is 50 Hertz.

    The hum is very audible through good headphones. When I connect to the amp it's there as well.

    With my P-bass, the hum disappears as soon as I touch the strings. It also disappears when I touch the mixer, or a pedal that's in the chain.

    When I play the acoustic bass with piezo, the hum is there even when I touch the strings. (But if the P-bass is standing by, connected to another channel of the mixer, and I touch its strings with a naked foot the hum disappears. No, I don't have a pic of this.)

    Are there any simple ways to solve this problem?
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  2. Stumbo

    Stumbo Guest

    Feb 11, 2008
    Have you tested the plug?
     
    instrumentalist likes this.
  3. How?
     
  4. Stumbo

    Stumbo Guest

    Feb 11, 2008
    th.jpg
    Something like this.
     
    LowActionHero likes this.
  5. Ah, you mean have I tested the socket. Well, can't do that right now, but I will.
     
    Last edited: May 19, 2019
    Stumbo likes this.
  6. When I test the socket, what am I looking for? What kind of electrical fault would lead to the humming problem?
     
  7. Just tested the wall socket I use for bass. Also tested my power strips.

    For AC Voltage, I get normal results. Should I test anything other than ACV?

    Elsewhere in the house, same results. This is the first time I've played bass in the kitchen.

    So it seems the sockets aren't the problem.
     
  8. Maybe it's just a faulty connection inside the mixer. But I've no idea how to fix things like that. :(
     
  9. Wasnex

    Wasnex

    Dec 25, 2011
    The tester @Stumbo showed tests for wiring faults. I does not test for the quality of the ground. A low quality ground can result in increased hum. A low quality ground may have high resistance and/or noise.

    Is this a new problem or has the mixer always hummed? Does the problem occur if you use the mixer in a different building?

    Passive pickups tend to pickup EMF that is in the room. Does the level of noise change if you rotate the direction the bass is facing, or change where you stand in the room? Shielding the control cavity may help.

    There may be nothing technically wrong with the mixer that can be repaired. I have a bunch of amps, and their noise rejection characteristic vary quite a bit. I play with an active bass that it usually pretty quiet, but if I stand close to some of my amps it picks up a lot of hum.
     
    instrumentalist likes this.
  10. BooDoggie

    BooDoggie Typical Dumb-ass with a degree

    Mar 29, 2014
    Hum like you are experiencing is often the result of improper or missing ground or earth connections. I see that the Netherlands is 230V 50Hz, so I cannot be certain of the exact way that things are wired there. When you touch the strings on the P bass you are completing the circuit to ground or eliminating RF signal from an outside source and sending it to ground. I have seen this problem quite often here in the states where people with older homes don't have proper grounding in the electrical service. Here they often remove the ground terminal from their power strip so that they can plug into the two prong outlets. (Not a good idea...)
    Sometimes the problem is just noise in the electrical supply in your area that is beyond your control. It could be a fault in the ground circuit in your house or maybe in the entire area. If you know a competent electrician have them check that all is well in your wiring, or call the local utility company and ask them about the problem you are having and see if they can help. I have run into situations where there are problems with the phase of the electrical service. Or it could be that the mixer you are using does not have a good ground isolation circuit...
     
    instrumentalist likes this.
  11. BAG

    BAG

    May 5, 2014
    New Zealand
    Some houses have very noisy power which can be caused by numerous things that are well above my knowledge level. Also, sharing a power strip with other things can cause noise issues. As an example, my Pbass is dead quiet at our drummer's place but in my studio (rented house) there is a very noticable buzz when i'm not touching something metal on the bass.

    Also, at our drummer's place one time I took power from the guitarist's power strip and it was very noisy. The next rehearsal I ran my power from the wall socket and got no noise. This was a surprise as it is a double outlet and the guitarist was still taking power from the same wall outlet.... it was only when plugging into his power strip (where he has his amp, pedals and the powered speaker for vocals plugged in) that I got the noise.
     
    instrumentalist likes this.
  12. Many thanks for the responses so far. Here are some answers to (stated or implied) questions:

    I bought it new some months ago, but am only now getting round to trying it out. Lesson learned: there's no going back to the store now.

    Haven't tried yet. There may be a good opportunity a week from now.

    This makes no difference.

    This makes no difference. Two floors down from the amp, the hum through the headphones is just as present as two feet from the amp.

    Quite possible. House is from 1968; wiring has been added to but never redone.

    Well I did (kinda) cheap out on this mixer, it cost €50 new. So...

    I am reasonably sure that isn't what is happening here. With or without power strip, no difference.



    All in all, the culprit looks to be either the house or the mixer.
     
    Last edited: May 21, 2019
    BooDoggie and Wasnex like this.
  13. Primary

    Primary TB Assistant

    Here are some related products that TB members are talking about. Clicking on a product will take you to TB’s partner, Primary, where you can find links to TB discussions about these products.

     
    Jun 21, 2021

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