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Ampeg SVT 4 Pro DI Hum

Discussion in 'Amps [BG]' started by James Simonson, Dec 15, 2013.


  1. James Simonson

    James Simonson

    Joined:
    Feb 2, 2008
    Location:
    Detroit, MI
    Disclosures:
    Endorsing Artist : Ernie Ball, LaBella Strings
    I did a search and got many results but no real answer. Wondering if something new has come up.

    I just bought a brand new SVT 4 Pro. It's a great amp. I'm into building DI boxes and I'd like to think I know a bit about ground loops and all that. I'm getting good results with a Counrtyman and a few other DIs out of the 1/4 inch line out or the effects send (that's a little hotter) but the xlr still buzzs. My first thought was to build a lifted xlr cable and not connect the shield. That didn't change anything. I lifted it at the wall too. No change.

    From what I've gathered, there is no ground lift switch because it is already lifted. According to my multimeter, Pin 1 does not touch the chasis.

    There's buzz out of the xlr out when the bass is unpluged and the mute switch is muted.

    Kind of a pulsated type buzz. Not really a hum.

    I'm running the xlr out into a simple Behringer mixer and some M-Audio powered reference monitors. It's my "real life job testing setup station" Everything else I own is quiet (or was made quiet) through this simple set up.

    When I use the pad knob on the front panel, it gets worse. The hum ratio sounds the quietest when the pad is at full volume. It's not the bass (I have several, passive Fenders) and the cables are all solid. It's actually a little better using the "post" button which I find somewhat unusual.

    The 1/4 inch out right next to xlr out sounds fine. The noise ratio/level there is what it should be. It must be the actual transformer or a loop created from the pad knob on the front?

    I feel like I've got a good handle on these problems and I've run out of options. Just a bad design?

    I've noticed others having the same problem. Was a solution ever discovered?

    I'm %100 convinced it's a design flaw or a common, internal problem.

    I guess the solution is to use a DI box but I don't really see that as the real way to fix what should be an air tight product.
     
  2. James Simonson

    James Simonson

    Joined:
    Feb 2, 2008
    Location:
    Detroit, MI
    Disclosures:
    Endorsing Artist : Ernie Ball, LaBella Strings
  3. Major Softie

    Major Softie

    Joined:
    Sep 23, 2011
    Location:
    South Lake Tahoe, CA
    The first thing I'd do is go into somewhere like Guitar Center and see if their demo does the same thing. If it did, I'd probably accept that it's a design flaw. If it didn't, I'd make Ampeg fix my amp.
     
  4. James Simonson

    James Simonson

    Joined:
    Feb 2, 2008
    Location:
    Detroit, MI
    Disclosures:
    Endorsing Artist : Ernie Ball, LaBella Strings
    Good idea. "GC Rentals"! hahahaha
     
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  6. James Simonson

    James Simonson

    Joined:
    Feb 2, 2008
    Location:
    Detroit, MI
    Disclosures:
    Endorsing Artist : Ernie Ball, LaBella Strings
    OK I'm not seeing snakes..

    Thank you Jerrold Tiers.

    The factory mod/simple fix was sent to me.

    It involves a tiny jumper and another simple wire routing.

    Thanks again!!
     
  7. hodgy

    hodgy

    Joined:
    May 5, 2004
    Location:
    Bothell, WA
    Disclosures:
    Tech Support- Ampeg/ Mackie
    Could you send that mod to me? I can't find it in our database!
    *Edit* Never mind, found it!
     
  8. Bunnfactor

    Bunnfactor

    Joined:
    Apr 5, 2012
    Location:
    Gardendale, Alabama
    What mods were required?
     
  9. chaosMK

    chaosMK

    Joined:
    May 26, 2005
    Location:
    Albuquerque, NM
    Disclosures:
    Hi-fi into an old tube amp
    Nothing wrong with using the 1/4 if it sounds good.
     

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