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Ground loop buzz

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  • Ground loop buzz

    When I was in the studio last month, playing scratch guitar tracks while we recorded drums, I got so much buzzing and crackle running my ART DST-4 and Peavey Rock Master together that I eventually unplugged the Peavey. It wasn't until we were done recording that I determined a ground loop issue to be the culprit. I guess it might be something else, but regardless of the preamp combinations (ART, Peavey, ADA MP-1), there was definitely buzz with two preamps connected...and the Peavey actually was crackling and dropping out. Once I got all my gear home, I noticed that the Peavey has a ground lift switch, which I hadn't realized in the studio. In any case, each preamp sounded fine if the other wasn't connected.

    There are two points of "contact" in my rig, where both preamps connect. First is a Sabine RT tuner, which has A/B switching. I run one preamp into each tuner input, and from each tuner output to one of the channels in my Carvin T100 stereo power amp. I am assuming that the power amp would be the most likely problem spot, as removing the tuner from the signal path made no apparent difference. Same results using a Morley ABY pedal.

    Since I don't really know anything about ground loops, I might be talking/typing out my ass on this one. I have read many comments and reviews suggesting that the Morley pedals sap a lot of the signal strength in the "Y" position, but I don't think signal loss would have been an issue through the Sabine, as it is either A *or* B, not both. I'm also concerned by the crackle and dropouts on the Peavey, but it works fine on its own. I would be disappointed to lose the simple A/B arrangement, and further concerned because I have a BBE 362NR on the way that could potentially contribute to further signal problems.

    Sorry for the novel. Any suggestions? (Note: I haven't used the rig since "discovering" the ground switch on the Peavey preamp, but I doubt that it alone would fix the buzzing issue.)
    sigpic

  • #2
    Id start at the beginning of the chain and wiggle connections and check each piece of gear. Go thru the whole rig one piece at a time. Check all the connections and lifting the ground on the Peavey might help

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    • #3
      Well, it's definitely only present when two preamps are on and plugged in at the same time. I've heard about various hum eliminators (not Hush, which I already have) but don't know anything about them or if they really can eliminate what I'm hearing. Only the Peavey has a ground lift switch, which won't help if I'm running the ART and ADA at the same time.
      sigpic

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      • #4
        I'd of course try using the ground lift on the Peavey and go from there. You "may" also try a cable on the ART that has the ground removed at one end and see if it works. If it is a ground loop issue, it's getting the ground through the chassis, and will probably still work

        Honestly, I'd say that a midi controlled looper that will totally isolate / seperate the preamps in their own loops is a good call for that type of rig.

        I'm not fond of A/B pedals and I would really not run them in a Y type of situation... as you are feeding outputs back into the others output. You will experience all sorts of ill stuff there.

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        • #5
          I had a ground loop in my rack. I could not find it for nothing. I tried a ton of things. In the end, the best way to debug it is to take everything out of the rack. Wire it up. If the hum is gone, you have things touching in the rack. You need to isolate mounting things in the rack. Mid-Atlantic makes a product called shoulder washers that you put on both sides of the rack ears for each screw. It has a little lip that keeps the screw from making contact with the rack ear thus isolating all your gear from contacing via the rack rails. Then you need to make sure none of the chassis' touch. A lot of folks suggest that you use ground lift 3-prong to 2-prong adapters on all of your rack gear except one piece - the manual for my Boogie 2:100 power amp mentions this as well (they of course suggest that the power amp get the full 3-prong treatment).

          Here's where I go the shoulder washers (remember you need 2 per screw/8 per rack unit):

          http://www.partsexpress.com/pe/pshow...TOKEN=53335279
          I want REAL change. I want dead bodies littering the capitol.

          - Newc

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          • #6
            Yep, I use those myself.

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