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Ampeg SVT 4 Pro DI Hum

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


  1. James Simonson

    James Simonson

    Feb 2, 2008
    Detroit, MI
    Endorsing Artist : Ernie Ball
    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

    Feb 2, 2008
    Detroit, MI
    Endorsing Artist : Ernie Ball
  3. 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

    Feb 2, 2008
    Detroit, MI
    Endorsing Artist : Ernie Ball
    Good idea. "GC Rentals"! hahahaha
     
  5. James Simonson

    James Simonson

    Feb 2, 2008
    Detroit, MI
    Endorsing Artist : Ernie Ball
    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!!
     
  6. hodgy

    hodgy

    May 5, 2004
    Bothell, WA
    Tech Support- Ampeg/ Mackie
    Could you send that mod to me? I can't find it in our database!
    *Edit* Never mind, found it!
     
  7. What mods were required?
     
  8. chaosMK

    chaosMK

    May 26, 2005
    Albuquerque, NM
    Hi-fi into an old tube amp
    Nothing wrong with using the 1/4 if it sounds good.
     
  9. 616slayer616

    616slayer616

    Oct 17, 2013
    Hi,

    sorry for digging out this thread but my SVT-4 Pro has the hum problem aswell.
    Could anyone please send me the fix?

    Or should I PM someone?

    regards

    Patrick
     
  10. baxter_x

    baxter_x

    Nov 27, 2013
    I think the SVT 4 pro is "famous" for having a faulty DI. Mine does have it too. I just can't use the DI on stage.
     
  11. Raw N Low

    Raw N Low If I can't hear it, hopefully I'll feel it Supporting Member

    Jul 16, 2009
    Denver, Colorado
    Is this a problem that only occurs on the non US versions of this amp? Mine seems to be fine as far as hum goes, although a bit weak on DI output.
     
  12. baxter_x

    baxter_x

    Nov 27, 2013
    I think I've read reviews of the US version, and people were saying the same about the DI. But that would be interesting to really check that out!
    How do you set the DI output? Is it fully opened, only 25%....?
     
  13. Raw N Low

    Raw N Low If I can't hear it, hopefully I'll feel it Supporting Member

    Jul 16, 2009
    Denver, Colorado
    It's on the "Line Out" knob for DI output. I find that it's not as articulate and is almost like Ampeg's Mid settings on most amps. You have to really crank it up to get sound and then you have to back it off to not be too loud. It's either hot or cold compared to dedicated DI's.
     
  14. Thummel

    Thummel

    Jun 24, 2007
    West Texas
    none
    The Line out on my 4 pro works great, clean and quiet. Perhaps you have power issues.
     
  15. baxter_x

    baxter_x

    Nov 27, 2013
    How high is your DI output?
     
  16. Abe Hughes

    Abe Hughes

    Nov 2, 2016
    Hey, I have one of these Amps and am having the same problem, but i can't find the mod you were talking about anywhere online. Where can I find it? I know this thread is pretty old, if I don't see any replies here, I may start a new thread.
     
  17. Abe Hughes

    Abe Hughes

    Nov 2, 2016
  18. baxter_x

    baxter_x

    Nov 27, 2013
  19. BasturdBlaster

    BasturdBlaster Supporting Member

    Feb 19, 2012
    Crandon WI
    Your Welcome!

    And also....WELCOME to TalkBass Abe!!

    This place is sorta like "Hotel California" for me,........... I can't seem to leave,hehehe;)