ABY Boxes, Ground Hum, Death, Shocking Questions...

Discussion in 'Effects, Pedals, Strings & Things' started by brewbaker, Mar 31, 2008.

  1. brewbaker

    brewbaker Supporting Member

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    I'm using a Whirlwind ABY box and got a ground hum from one of the two amps I'm going to. They are both plugged into a strip that has a 3 to 2 adapter on it because my house has old wiring. So I put a 3 to 2 adapter on one of the amps and voila the hum was gone. But I detected a shock when touching one of the cable jackets. So, I put an adapter on the other amp as well. No hum, no shock. However, I'm still paranoid that this may be a dangerous way to eliminate the hum. Any info would be appreciated. I may buy a Tonebone box instead.
     
  2. Shnook

    Shnook Supporting Member

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    Is the wiring in your house grounded properly?
     
  3. brewbaker

    brewbaker Supporting Member

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    I assume so--it's a rental so I wasn't involved in the fine points. Some of the outlets are three prong and some are not. How do I tell?
     
  4. Shnook

    Shnook Supporting Member

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    Go to the hardware store and get a ground tester. I bought mine for $6 or so. I test every outlet with it before I plug in my amps. Espeicially when playing out somewhere. My house was built in the 40's and I found some of my outlets were grounded and some were NOT! I ASSumed that since they had 3 prong holes in some outlets all was good. Not so.
     
  5. wahwah

    wahwah Member

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    As I understand it, you need to safely isolate the ground on one of the outputs, because what you have there is an earth loop. By lifting the ground on both amps with adaptors, you are opening up the possibility of YOU becoming the earth, which will probably result in death. Whilst death can potentially increase album sales, it will also seriously affect your future tone making capabilities.



    Cheers...................................wahwah
     
  6. brewbaker

    brewbaker Supporting Member

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    Great suggestions--I'm off to the hardware store. Thanks.
     
  7. stinkfoot

    stinkfoot Member

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    Ground loops occur when the amps' grounds are connected through more than one path (both through the safety ground and via the common ground in the ABY box), and they will result in a hum when there's a voltage difference in the ground potential of the two paths. The bigger the voltage difference, the louder the hum. The shock you got was that voltage difference, passing through you to ground.

    By removing the safety ground on one of the amps, you eliminated one of the paths to ground, and with it the hum. But there's a reason it's called safety ground - if you need to eliminate one of the extra ground paths, it's far better to do so on the signal side. It sounds like you need an isolated ABY box, where the A and B outputs are transformer isolated from each other (so they can't create any ground loops).

    /Andreas
     
  8. brewbaker

    brewbaker Supporting Member

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    So I tested my outlets and even though they are to prong the boxes they're in are grounded. So I'm going to change the outlets to 3-prong grounded. Then all the amps will be plugged in the same way with no adapters. My question now is will there still be a ground loop if I'm using the Whirlwind box which apparently has no provision for isolating the inputs? Is the only solution to get a splitter that has at least one isolated input? I'm thinking about the Radial Big Shot ABY.
     
  9. kp8

    kp8 Member

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    That was *very* clearly explained. Bravo & thank you for taking the time to type that. I would have taken me twice the amount of words you used and would have been half as articulate.
     
  10. stinkfoot

    stinkfoot Member

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    If you connect both amps to the safety ground (like you should), the ground loop will be there, yes. The Big Shot is one of the ABY's available with isolated outputs, so give it a try.

    Thanks! I tend to use lots of words too, so that was probably one of the more concise moments... :AOK

    /Andreas
     
  11. brewbaker

    brewbaker Supporting Member

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    Follow-up to my hum situation. I got the Radial Big Shot ABY. First reaction is that it does eliminate the hum in the two amp set up by isolating one side of the A-B outs. But it does radically change the tone of that amp. The manual says you simply adjust the amp to compensate for this. I'm going to spend more time with it but I'm skeptical. It's pretty different. Buyer beware I think.
     
  12. ylo

    ylo Member

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    I suggest the Switchbone (or equivalent such as the Framptone), which is an active version of the Big Shot. This will drive the signal from your pedalboard to your amps without any loss of treble from cable capacitance. The Switchbone also has a transformer for isolation.
     
  13. mike@nortoncable.com

    mike@nortoncable.com Member

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    The Framptone switchers are awesome, I had problems like this before using a Morley, with the heavy duty transformer & Ground lifts per output on the framptones- that bridges the gap :)
     
  14. SteveStevens

    SteveStevens Member

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    I did a recording on Tuesday and we ended up splitting the signal to two amps with the Humdinger (available at www.thegigrig.com). The engineer was extremely pleased with the result. For comparison, we tried the two outs from my Boss RV-5. No dice. It was RF City and I got a big shock when I went to plug in the connection! Switched back to the HD and he said he had never been able to get such a quiet and musical result from two amps. Look at my signature and be suitably skeptical as I am an endorser for the Gigrig. But it still is the best thing out there.

    Steve
     
  15. walterw

    walterw Gold Supporting Member

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    i would think you could also get good results in that situation by cutting the ground connection of one of the signal cables coming from the splitter to one of the amps. i would guess that cutting the ground at the splitter rather than the amp will leave the sheild grounded from the amp itself, so it would still do its job.
     
  16. spentron

    spentron Member

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    ^--that would put all the hum in one amp with both grounded, worse with one grounded. Otherwise, it kind of demonstrates the issue that you could cut a ground on a sensitive signal cable and it make very little difference.

    I can't see why there'd be a change in shock by lifting both grounds to the power strip if the strip not grounded, unless something else is also plugged in. Lifting grounds is not completely safe, but it helps if you plug EVERYTHING in before plugging to the wall, and leave it all in until unplugging power.

    The ground loop noise is due to signal induced into the amp chassis by magnetism. If you plug a cord into the amp input and touch it to various portions of the amp case including the ground pin, it will probably make different noises depending on location. Another issue regarding shocks are noise capacitors to line such as some have amps have so-called ground reverse switches for, these usually make shocks worse, but are effective on noise sometimes -- although they would only make 2-amp hum worse.
     
  17. LavaMan

    LavaMan Gold Supporting Member

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    Need an A/B/Y with an isolation transformer...
     
  18. SteveStevens

    SteveStevens Member

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    Hey Mark! The Humdinger has exactly that...but then so does your Lavaflow, now doesn't it?;)

    Steve
     
  19. walterw

    walterw Gold Supporting Member

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    huh? i thought ground loop hum was created by ground loops.
     
  20. NortheastHick

    NortheastHick Supporting Member

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    For $60 you cant beat the Radial ABY. No ground loops,no power needed,a very small foot print, and extremely durable. I have had great success with mine..And a lot of FUN mixing amps.
     

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