Hum Cause/Fix?

Discussion in 'Recording/Live Sound' started by Pretzmidtown, May 3, 2015.

  1. Pretzmidtown

    Pretzmidtown Member

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    This is for all of you experienced with amp noise, live sound, etc!

    I live in a 1911-built house, so, there-in lies perhaps my first challenge. I'm trying to home record more but I just CAN'T get rid of electric noise/hum no matter if I'm recording/mic'ing my amp (Peavey Classic 30) or just going pedalboard into amp sims on the MAC (Garageband, or anything else). The outlets are all 3-pronged.

    I've done some comparisons. Tried different outlets in the house but they are all old, so might be the same everywhere. When I plug my Classic 30 in and don't have a guitar cable in, I can crank it to 12 and it's completely normal, just slight normal speaker hiss awaiting beautiful guitar glory to input it but zero hum. As soon as I plug a guitar cable in the input jack (tried many different cables, including "good" ones), I immediately hum like crazy, no matter the cable, no matter the guitar. I can't even turn it past 1 hardly without loud buzzing/hum.

    It's the same with my pedalboard (Voodoo Power Plus 2 all isolated) even if I go direct into DAW and avoid damp –*I can't record through my pedalboard because of the noise right now (same, hum).

    Is there some way I can eliminate this? Or am I just screwed because it's an old house? I played my Classic 30 out a few weeks ago and there wasn't really any hum (non 1911-built venue).

    Deeply appreciate your thoughts and help! I can't really record until I get this fixed :( :beer
     
  2. 335guy

    335guy Member

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    You may need to have an electrician come by and diagnose the problem. It sounds like a grounding problem, but it could be something else, like too many rooms on the same circuits. To completely upgrade the home's electrical would probably be an expensive proposal, and if it's not your home ( are you renting? ), a cost that the landlord may not want to foot the bill for. But it may be possible to have a well grounded, isolated circuit run to the room where your recording in. Consult an electrician would be may recommendation.
     
  3. Pretzmidtown

    Pretzmidtown Member

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    Thanks much 335 ... yeah, kind of what I was afraid of! These old houses, SMDH :( I rent, so limited a little in options of repairing. I might try the Hum X and see if that works, though!
     
  4. oldhousescott

    oldhousescott Silver Supporting Member

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    You might want to investigate a balanced power transformer unit. These are not your typical power conditioners, they are isolation transformers with balanced outputs to reduce 60Hz hum.

    Toroid Corp sells a line of balanced power transformers at a decent price. You can get a 1.5kVA unit for about $500. That looks like a pretty good deal to me.
     
  5. LSchefman

    LSchefman Member

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    I use balanced power in my studio too, but balanced power won't solve ground loop issues if that's what you have. Those can often caused simply by interconnecting gear that isn't properly designed (yes, it happens!).

    It's actually more likely that the problem is a simple ground loop than a fault in your house wiring. Step one, of course, is to verify that your outlet(s) have proper grounding. This is done with a 5 buck item called a Receptacle Tester. You get them at the hardware store, and you can pick up a couple of 3>2 ground lift adapters while you're at it.

    You test the receptacle for grounding by simply plugging it into an outlet, and its lights tell you if the outlet is wired properly and grounded. Simple. Next you test for ground loops.

    Leave your audio cables wired in place.

    Put on headphones, and turn them up with nothing playing. Piece by piece, unplug each piece of gear from your power strips. This will tell you if something is causing a ground loop. If the hum is reduced, or stops altogether, when you unplug something, you've found your source of the ground loop (yes there can be more than one source of loops in a rig). You'll double check this later by plugging it back in with a ground lift adapter (a 3>2 plug adapter).

    Obviously keep your computer audio interface plugged in. But computers and computer monitors are a notorious cause of ground loops, so be sure to unplug your computer, too, while leaving the interface plugged in so it powers your headphones. Same with your speaker monitors.

    Remember to turn down the headphone volume or take the cans off your head as you unplug each piece of gear to protect your ears from potential loud thumps or pops.


    It's usually pretty easy to find the offending piece of gear this way, because once you unplug the gear causing a ground loop, the noise goes away (or is reduced if you have more than one loop). There are lots of fixes for ground loops that work, but step one is finding the problem!

    Then as a TEMPORARY measure, you can put a 3>2 adapter on the gear that caused ground noise, and see if it still causes with the adapter when you plug it back in. If doing so allows you to have the gear plugged in without noise, you've found a temporary fix for your ground loop. You will have to do a permanent fix before being safe with the gear, but at least you know what to work on.

    Do this with each piece of gear.

    Once you've got this sussed out, there are products on the market that are designed to isolate the grounds and break the loop, and are a permanent fix. These can be little transformer boxes you plug the audio cables into, or they can be stuff like the Hum-X. Sometimes a fix is as simple as lifting the grounds on one end of balanced lines. This is effective with XLR or TRS cables, but much less so with TS connections. Sometimes not only does the 3 prong plug need to be plugged in, but an additional grounding wire needs to be attached to a grounding block, that in turn needs to be connected to a solid Earth ground, like a cold water pipe. As I said, each studio has its own gremlins.

    The point is, a bit of experimentation is often necessary to find the cause of the loop and the fix.

    Fortunately, it's not difficult to find the loops using the plugging and unplugging technique, and after you do, there's a lot of information out there on the proper way to fix it.
     
    Last edited: May 4, 2015
  6. Bassomatic

    Bassomatic Silver Supporting Member

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  7. Pretzmidtown

    Pretzmidtown Member

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    This is crazy helpful, thanks guys. I'm hoping it doesn't end up requiring an expensive fix, but it sure is infuriating that I can't play or record silently. (silently, meaning without HUM and noise, that is :) You put a lot of experience and thought into these responses and it is going to be really really helpful to me ... going to start testing things out more specifically as you mentioned tonight! Fingers crossed.
     

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