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Need Help! Amp issues troubleshooting

Discussion in 'Amps [BG]' started by Masher88, Nov 2, 2013.

  1. Masher88

    Masher88 Believe in absurdities and you commit atrocities

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    Here's my rig that I've had for years with no problem (signal chain is in order that is listed):

    -G&L L-2000 bass (new battery in pre)
    -Korg rackmount tuner
    -Tech21 Sansamp RBI preamp
    -QSC PLX 3002 (dip switches set to 4 ohm bridged)
    -Ampeg 410hlf cab (4ohm)

    Rig performs perfectly at my home and at the practice spot and has for years.

    1. At a show, soundguy plugged a xlr into the direct out of the sansamp. Rig got really quiet and distorted after a little while of playing. Suffered through the show. Bass seemed to sound fine through the PA...I wasn't in the crowd but the cellphone recordings sound ok.

    2. took rig back to practice after show...works just fine...loud and proud. Months go by....

    3. Recording at studio...engineer plugged into direct out of sansamp...worked ok for a little while then got quiet and distorted. Different cabs, though. Ampeg 115 and 410 both 8 ohm connected down to 4. Tried unplugging Direct XLR and I think we tried a direct box...still quiet and distorted. Rerecorded all tracks with different amp...What Da heck is going on?

    4. Got home, set up rig...worked fine.

    5. back at practice spot...works fine for months

    6. Last night's show back at same club as before. Told sound guy to mic my cab....he gave me a direct box to plug into before my rig in the signal chain instead. Turned on rig and it's quiet and distorted again, but over the PA sound is good. Suffered through the show with only being able to hear the bass through the PA speakers...not through my cab.

    7. Just now set up my rig in the garage...sounds fantastic. Super loud and clear.
    --------------------------------
    Does anyone have ANY guesses on what is going on here??

    From now on, I'll be I guess I'll be adamant about using a microphone for my cab. I'd really like to know what's happening, though. Maybe it's just the act of splitting the signal between a PA and the Preamp?
  2. Hopkins

    Hopkins Supporting Member

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    The fact it happened with an external DI is very strange. Do you push it harder in a live setting than you do at practice?
  3. Masher88

    Masher88 Believe in absurdities and you commit atrocities

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    Glad you mentioned that. I took care not to touch settings from practice on Wednesday to the show last night. My rack case has a cover on front so the knobs couldn't be bumped. So, no the settings were from practice volume where the rig performed flawlessly for more than 2 hours.

    Actually, we turned DOWN for our second run through of the setlist at practice, so the volume was LOWER than I had it in the past.
  4. B-string

    B-string Supporting Member

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    Just for kicks go direct to the RBI, leave the tuner out of the chain.
  5. Cirk

    Cirk

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    I'm probably wrong, but have a look at the solder joints on your cables. While you're at it, clean all of the jacks on your gear. Hey, it couldn't hurt!
  6. Hopkins

    Hopkins Supporting Member

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    That's a very odd problem, be sure to let us know what you find out.
  7. Jeff Scott

    Jeff Scott Don't just TalkBass - PlayBass! Supporting Member

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    My first thought was something phantom powered related until the post about a DI tried before the amp causing the same issues. :meh:
  8. Masher88

    Masher88 Believe in absurdities and you commit atrocities

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    Is there a possibility that it's the simple act of splitting the signal from my bass that the amp is not liking?
  9. bgavin

    bgavin Supporting Member

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    Start at the basics:
    Link to RBI Owners Manual

    OP, I assume you are connecting the RBI to the power amp using a 1/4" cable.
    Looking at the hookup diagrams in the manual, this should be the 1/4" Sansamp Output jack.
    From the same diagram, the console connection uses the Sansamp XLR output. Not the Unaffected.
    Take note of the XLR output button. Is FOH looking for MIC or LINE level output.

    On the front of the RBI, there are two volume controls: XLR and LEVEL.
    You can adjust the stage amp independently of the XLR signal sent to FOH.
    Note: The Sansamp front button must be engaged.

    Tech21 does not make any mention about +48v phantom being a problem on the XLR connection.
    I would email them and find out for certain.
    My SWR IOD will smoke if +48v is applied to its DI out.

    [ edit ]
    I sent an email to Tech21 to get the answer about phantom power on the XLR connection.
  10. Masher88

    Masher88 Believe in absurdities and you commit atrocities

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    "I assume you are connecting the RBI to the power amp using a 1/4" cable.
    Looking at the hookup diagrams in the manual, this should be the 1/4" Sansamp Output jack.
    From the same diagram, the console connection uses the Sansamp XLR output. Not the Unaffected.
    Take note of the XLR output button. Is FOH looking for MIC or LINE level output."

    Yep, Yep and Yep. I wasn't sure what was going on the first time, so I skipped the Direct Sansamp XLR Out this time. I wanted him to just mic the cabinet, but he didn't want to.

    The other night, he ran me through an outboard direct box before my signal hit the rig at all. Still sounded bad. really quiet and distorted. Unfortunately, there wasn't enough time to check right then and there what happened if I skipped all of his gear and just ran my rig independent of PA (maybe a power issue at the club? Although, the guitarists are fine), but it sounds fine here at my house now.

    Odd.

    Thanks!
  11. bgavin

    bgavin Supporting Member

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    I just got this email back from Lloyd at Tech21 about phantom power on the XLR connection:
    As to the club problem, I would set up the rig without any connection to FOH.
    Test the rig to see if if the problem exists... if so, wall power is the only difference.
    Radio Shack makes a cheap safety checker. Mine is used at every venue, every time.

    If your stand-alone club sound is proper, then hook in the DI between instrument and Sansmp.
    If it goes bad, the DI box itself is the problem.
    Unplug the cable from FOH to the DI box, to see if FOH is the cause of the problem, or the DI box itself.

    My Countryman Type 85 sounded like ass when running on the internal battery. It wanted phantom power. YMMV.
  12. Hopkins

    Hopkins Supporting Member

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    How could the FOH cause his stage rig to sound terrible, but the DI still sounds fine through the FOH. It gets even weirder when it happened with the DI on this RBI, and an external DI.

    The only thing I can think off is bad power, but wouldn't that have messed with the DI on the RBI?
  13. orangejulius3

    orangejulius3 Supporting Member

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    Maybe cleaning the pots on your bass with DeOxit. There might be a dirty pot that's not sending the signal correctly.

    I had the exact rig, a few years back, but slightly different.
    Mine was:
    Korg DTR 2000
    Sansamp RBI
    DBX 215 EQ
    QSC PLX 1602
    I plugged in to the sansamp RBI first and sent a signal to the tuner.

    If you are using Banana plugs, that means your using an adapter. Get rid of it. I had a similar issue once at a gig, so I un-bridged the amp, took off the banana plug adapter, and used my 1/4" speaker cable. Problem went away.
  14. bgavin

    bgavin Supporting Member

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    The first part are the diagnostic steps to isolate the problem.
    If being connected to FOH is the cause of the problem, the "why" comes next.

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