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Underpowered or broken?

Discussion in 'Amps and Cabs [BG]' started by MyrskyVaris, May 21, 2011.


  1. MyrskyVaris

    MyrskyVaris

    May 21, 2011
    Hi all,

    I have a Trace Elliot AH200 (GP12 Preamp) that I bought second hand today. I have connected it to a Marshall MBC410 cab. The TE is rated at 200w, 4ohm. The MBC is 600w.

    I get a terrible distortion when I play through this combination. The sound is fuzzy, and there is an odd distortion that almost sounds like a torn speaker. The louder I play my bass, the worse the sound.

    The higher I turn the gain and volume on the TE the better the sound, but even at max on both it sounds bad.

    I used my Kustom 80w 8ohm to test the MBC, and it sounded quite sweet, but I kept the volume low and played only for 10 seconds or so. Worried about doing damage to the cab because of the ohm mismatch.

    So, am I underpowering the cab, or is the TE faulty? Or perhaps both? Any advice appreciated.

    Stormie
     
  2. Underpowering is a MYTH

    The problem lies elsewhere................
     
  3. RickenBoogie

    RickenBoogie

    Jul 22, 2007
    Dallas, TX
    You must first determine which piece is at fault. Process of elimination.
     
  4. coreyfyfe

    coreyfyfe Supporting Member

    Nov 19, 2007
    boston, ma
    You wouldn't damage a cab with an impedance mismatch, you'd damage the head, and then the only case would be if you used a lower-than-rated impedance on a SS head or a mismatched impedance an amp with an output transformer (tube amp).

    What kind of bass are you playing? Passive or active? If active have you checked the battery?

    That MBC cab should be fine with that head as long as you aren't cranking every knob to max and playing like a mad man.

    Try to narrow down your options. So the cab sounds fine with another head, or at least it did with a short test (you should try it again). Try the head through a different cab if you can. Try a different bass, different cables, etc.
     
  5. MyrskyVaris

    MyrskyVaris

    May 21, 2011
    I'm using an active bass. I have checked the cables, changed the battery, changed cables and the result is the same. I've run a guitar through the passive input on the TE and get exactly the same strange distortion.

    I have played the Kustom 80w head through the Marshall cab twice now, once for 10 seconds, once for a couple of minutes, and there is no problem.

    It's only when I use the TE.

    I don't have another cab to test the TE head on. But I would say the problem lies with the TE.
     
  6. Does the head have an effects loops ?

    If yes, try using a short instrument cable, and connecting one end to the send & the other to the return (to close the loop).

    If that clears up the distortion, you need to clean your input/output jacks.

    If no FX loop, try taking a cable and running it in and out of each 1/4 in/out a couple of times.

    Oxidation can make for bad connections and cause distortion.
     
  7. MyrskyVaris

    MyrskyVaris

    May 21, 2011
    Yes it does. Thanks - I will try that.

    I have sprayed switch cleaner on all the sockets and EQ, buit that didn't help.
     
  8. If you do have cleaner, give a little spray into each in/out before running the cable through it a couple of times.

    Good luck !
     
  9. MyrskyVaris

    MyrskyVaris

    May 21, 2011
    OK. Sprayed more switch cleaner and inserted/removed jack a few times.

    I attached a cable between FX send and return.

    No change! There is this almost squeal like sound that occurs when I pluck the string, and dies away before the note dies.

    I tried recording the sound on my phone, but the squeal tone does not record on it.
     
  10. Jaco who?

    Jaco who?

    May 20, 2008
    I don't understand the ohms mismatch thing with the Kustom; It's pretty rare that an amp's minimum impedance is 8 ohms. If it sounds like a torn speaker, it probably is, and doesn't occur with 80/4 - which is a whoppin' 20 watts. As always, though, I could be completely wrong.
     
  11. MyrskyVaris

    MyrskyVaris

    May 21, 2011
    I'm erring on the side of caution as I don't understand ohms as it relates to attaching heads to cabs.

    I have checked the speakers and the tweeter, all appear to be in good condition. No signs of torn speakers at all.

    But having said that, it sounds like a torn speaker, but not exactly like it. It's the closest I can describe it.
     
  12. It's almost impossible to diagnose a problem properly across the internet but - what is the impedance of the cabinet?
     
  13. MyrskyVaris

    MyrskyVaris

    May 21, 2011
    4 ohm
     
  14. Then you should get the full output of the head. To me it sounds like you may need more power and are running out of headroom. I would take the amp in to a tech and have it checked out to be sure.
     
  15. MyrskyVaris

    MyrskyVaris

    May 21, 2011
    Thanks Paul. That does seem to be the only way forward.
     
  16. Hi.

    Judging by Your handle, Tervetuloa TalkBass forumiin MyrskyVaris.

    Since You have done the process of elimination, it's pretty safe to say that Your amp is malfunctioning, as simple as that.

    Taking it to a tech, or better yet, to the place You purchased it would be the best course of action.

    Regards
    Sam
     
  17. Munjibunga

    Munjibunga Retired Member

    May 6, 2000
    San Diego (when not at Groom Lake)
    Independent Contractor to Bass San Diego
    Maybe your active bass is overdriving the input of the TE.
     
  18. Steve

    Steve

    Aug 10, 2001
    So do I and that thing is LOUD and clean.
     
  19. Rune Bivrin

    Rune Bivrin Supporting Member

    Oct 2, 2006
    Huddinge, Sweden
    That sounds a lot like cross-over distortion. A regular class-B amplifier needs a certain amount of idle current through the output transistors to work correctly. When that is missing the bottom of the sine wave is cut off, resulting in a distortion that sounds like crap, and the sound dies off very abruptly.
    The louder you play the less prominent this becomes.

    This could be because of a bad bias circuit or incorrectly replaced output transistors (putting in darlingtons instead of regular transistors)
     
  20. Tracebassplayer

    Tracebassplayer Sometimes Darkness Can Show You The Light.

    Dec 15, 2000
    Portland, OR
    Set your input switch to ACTIVE for your active bass.
    turn MUTE on and volume at Zero, set the EQ flat (off) and presets off. remove the effects from the loop.
    Play the bass (it's volume full on) and adjust the Input GAIN until the red LED just flickers on a strong note or if you have the 5 LEDs - untill the yellow LED just flickers with NO RED.
    Now that your input is dialed into optimum settings for that bass (Per the manual).
    Unmute the volume side and turn up to 2. it should sound pretty clean.

    Make sure your 8 or 4 ohm speaker cab is plugged into a "speaker out" not one of the the others (I've seen this before so don't laugh, people do it), The amp head will take loads down to 4 ohms. Two 8 ohm cabs daisy chained or one 4 ohm cab alone - less than 4 ohm loads will damage the amp output section.

    Also, if it's an SMX, it has a built in cross over and you want to plug the full range speaker into CH A. Ch B is where the cross over send the lows so your 10"ers don't fart... which is the sound you are probably trying to describe as a torn speaker, I think...
     

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