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snap, crackle, pop!

Discussion in 'Amps and Cabs [BG]' started by mntngrown, Feb 20, 2008.

  1. mntngrown

    mntngrown Supporting Member

    Aug 18, 2007
    Santa Cruz Ca
    Hello you engineer angels and bass amp audiophiles. Once again the clueless ask for your help.
    I bought a crown power amp and a tech 21 rbi, and have done my best to follow the manuals. I plug my bass into the front 1/4 inch input on the RBI, and connect the RBI to the Crown via the 1/4 output of the RBI, into the combo 1/4/slr input of the Crown with a balanced 1/4 cable, (one of the Crown manual's suggested options). I noticed the RBI manual only claims the xlr output to be "balanced". I was saving that output for connection to house PA, but since the crown manual says to use "balanced" out into their amp, maybe I will switch to xlr connection from the rbi. Currently I get a lot of snap crackle pop if I wave my two G&L L-2000 bass headstocks toward the amp/speakers, and other ground issue noises touching the metal control knobs. The funny thing is I get almost no problem when I plug in my Carruthers 5 string, which has a well shielded contol cavity. This link one of you experts provided on TB says you can disconnect the shield of a balanced cable at the amp input as a possible solution? http://www.rane.com/note110.html
    Any hands on experience about where I should start to get rid of the noise?
  2. Are you sure the problem isn't the bass? Maybe a ground problem in your electronics or even a shielding issue.
  3. mntngrown

    mntngrown Supporting Member

    Aug 18, 2007
    Santa Cruz Ca
    The bass is part of the equation but one l-2000 is early 90's vintage and the other is almost new and they both make the snap crakle pop, to me representing average shielding. There is copper on the face side of the cavity only. The Carruthers is shielded on all surfaces, but this suggests the work needs to be done downstream. Apparently a powered preamp plugged in with its own ground, then connected to a power amp with its own plug and ground, both of which chassis's are bolted into an aluminum alloy rackmount frame make for ground loop problems. This is why GK has a ground lift button on there amps which can alleviate this problem when the DI is sent to a PA. Any more ideas. I could get one of those simple adaptors that eliminate the ground portion of a plug, but the Rane link says that is not safe.
  4. bongomania

    bongomania Commercial User

    Oct 17, 2005
    PDX, OR
    owner, OVNIFX and OVNILabs
    I don't know, it sounds like both of your G&L's are badly grounded and shielded (they are known for that). The first thing you need to do IMO is fix/upgrade both the grounding and the shielding inside both of the G&L's.

    The unbalanced output of the preamp feeding the balanced input of the power amp is an issue worth exploring on its own, but it is not related to any of the snap crackle or pop. If anything it would cause a lower output level from the preamp, or higher susceptibility to line noise if you used a long cable to connect them. But no popping noises.
  5. mntngrown

    mntngrown Supporting Member

    Aug 18, 2007
    Santa Cruz Ca
    Thanks, I'll look into shielding.

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