Unwanted humming when using two amps with HB II?

Discussion in 'Electric Instruments' started by Audie, Jan 26, 2015.

  1. Audie

    Audie New Member

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    Anyone else have/had this problem? If i play my HBII thru either the acoustic or electric amp alone everything is fine. When i use both amps I get that awful low hum thru the electric amp. It does not go away until I unplug the acoustic amp cable from the guitar. What's going on? How can I remedy?
     
  2. watelessness

    watelessness New Member

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    Ground loop issue?
     
  3. shinksma

    shinksma What? I get a title?

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    Yeah, sounds like a ground loop. Are both amps plugged into the same outlet/power strip? Can you (temporarily) "lift" the ground on one of them? If the hum goes away, it indicates you are providing a common ground for both amps via the unlifted one of them. Which means one of them has mixed common and ground improperly, IMHO.
     
  4. Audie

    Audie New Member

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    I don't think I know what a ground loop issue is. Each amp is plugged in on a different wall, maybe the same circuit though. So how do I fix?
     
  5. shinksma

    shinksma What? I get a title?

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    A ground loop is caused by the ground circuits of the equipment going back to the main panel via two different paths (and then onto the actual ground connection, a big rod inserted into the ground near your house/building).

    Because the grounds go via two different paths, they effectively form a giant loop of wire, going from your guitar, out one amp to the wall to the ground, back to the other wall to the other amp to your guitar. This giant loop encircles other electromagnetic signals, including other house/equipment wiring. Those EM sources, by simply being there, cause a small signal to be self-generated within that ground loop, which feeds back into the audio signal as a hum (at 60Hz for North America, 50Hz for Europe) - sounds like an out of tune "low E" kinda hum.

    Even if your amps are on the same house circuit, there might be enough ground-loopiness to cause a hum.

    Try plugging in both amps into the same power strip or extension cord, and if possible, keep them near each other.
     
  6. Audie

    Audie New Member

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    Thank you, I will try that out.
     
  7. ViperDoc

    ViperDoc Plugged In.

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    Look on the back of your amps and look for a Ground Lift switch. Try different settings and check to see that improves it.
     
  8. LSchefman

    LSchefman Hears Tones

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    The loop is caused not at the outlets or power strip but because one guitar is interconnecting two amps and the guitar cables create the ground loop.

    The best way to deal with a ground loop using two amps is to use a passive or active transformer to isolate the signal ground coming via the guitar cables to both amps, and still keep both amps properly AC grounded. They aren't expensive. I use a Lehle that sits on my pedalboard with its isolated output jacks. An Iso box has a switch to lift and isolate the signal ground for one of the connected amps. The isolation happens because the signal going to each amp is split inside the box and the Iso transformer inside it uncouples the ground connection caused by the cables.

    http://www.musiciansfriend.com/[email protected]^PLA-device^t-adid^53736456387

    It's not about home wiring really, it's all about chassis grounding in amp design. You can drive yourself nuts with power strips and such, that stuff is random hit or miss. If you have a ground loop because one guitar is connected to two amps, the cure is at the guitar cables to amps connection, and an isolation box breaks the loop there.

    An iso transformer is the is the real deal cure for not much more than $150.
     
    #8 LSchefman, Jan 26, 2015
    Last edited: Jan 26, 2015
  9. Egads

    Egads Happy

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    Another option that I think is a must have for mag/piezo guitars is a good DI with a ground lift.
     
  10. shinksma

    shinksma What? I get a title?

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    Yep, both Les and Egads have suggested solutions that should eliminate any hum when a single guitar output is split to two different amps. But Les, how would one use that device when using the piezo output and the elec/mag output from the same guitar going direct to two different amps?
     
  11. vchizzle

    vchizzle Birdman.

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  12. Audie

    Audie New Member

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    Solved my problem for 69 cents. Thank you guys. No more hum!
    [​IMG]
     
  13. ViperDoc

    ViperDoc Plugged In.

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    LOL!
     
  14. Audie

    Audie New Member

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    Yeah I know, crazy, right! The three prong amp plug plugs into the backside and ground is eliminated (or can be connected to the protruding tab).
     

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