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Amp (or Cabinet) Problem Suggestions

Discussion in 'Amps and Cabs [BG]' started by terser, Jan 3, 2003.


  1. terser

    terser

    Dec 23, 2002
    South Jersey
    I just got an SWR 350 amp (red face model) that was sitting on a shelf unused since 1998. I ran it into my Ampeg 4x10 (8 ohms) and SWR Workingmans 1x15 (which I just got used from musicgoround.com). It turns out that the 1x15 has a resistance of 4 ohms so obviously somebody changed the speaker in it because it should be 8 ohms. The speaker has no markings. The combined resistance should not be a problem since the SWR 350 is rated for 2 ohms. My problem is that the 1x15 output is very fuzzy/distorted pretty much throughout the range of bass notes and the 4x10 is fuzzy when I pluck the low E string. The fuzziness is usually there but sometimes goes away. I took the amp back and A/B'd it with my 1x15 and a new one and it worked fine with the new one, however the 1x15 still had the distortion even when I replaced the speaker with a reconed 1x15 from a SWR Son of Bertha (upgraded 1x15). I hate to think that both cabinets are blown because the Ampeg sounded fine before. I replaced the instrument cable with a Planet Waves and both equipment cables with Monster's and tried others to eliminate those as the problem. This amp also has a tube pre-amp. I replaced the tube 3x's with no success. Anybody else ever had a similar problem. Sorry for the long, first post.
     
  2. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    That wasn't really a very long post...

    Anyway...when you "took it back" did you bring your bass along and use it? If not, does your bass have a preamp that perhaps needs a new battery?

    Keep in mind that a speaker with a nominal 8 ohm impedance will have a dc resistance less than 8 ohms. It could very well be the original speaker...

    Did you try your cabinets with a different amp (known to be good) with an instrument that is either passive or known to have a strong battery?

    Are you sure that you're using speaker cables to connect the amp to the cabinets and not instrument cables. Instrument cables should never be used to connect amplifiers and speakers together as they are made from small gauge wire and can short out potentially damaging your amp.
     
  3. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    A couple of other things...

    Is the peak light flashing? If so, turn down the input gain.

    Also pull out the effects blend knob to disable the limiter.

    Let me know what happened...
     
  4. terser

    terser

    Dec 23, 2002
    South Jersey
    Thanks for the replies. I did try out the new cabinets using my bass and the suspect amp. It's a passive Fender Jazz. Also, I tried out two different new amps with my 1x15 cabinet at the music store I bought the amp from, an SWR 350x and GK700RB. They both produced a buzzing from the 1x15. The music store owner was more than accomodating, spending over two hours with me trying to diagnose the problem and lugging big cabinets around without taking a penny from me (Martyn's Guitars in Lansdale, PA) and letting me try the Son of Bertha replacement speaker.

    When I checked the resistance of the used 1x15 it was 4.6 ohms so I'm pretty sure that it was a replacement speaker. As a matter of fact, the wires to it were reversed as I found out after I checked it with a 9V battery. Also, I made sure that the cables weren't the cause of it first as I previously had a (new) miswired equipment cable blow out a Workingmans 12 combo to the tune of $75. Any other ideas you folks have would be appreciated. And I'm spent...
     
  5. terser

    terser

    Dec 23, 2002
    South Jersey
    Also, I made sure that the peak gain light is not flashing (I rarely run both the preamp and master volume more than 50% as it tends to cause the wife and kids to claim abuse although I tend to start to giggle my ass off). Also, I tried disabling the limiter to no avail. As a matter of fact, I bypassed the preamp to make sure that wasn't the problem by using the effects blend, and it still showed the same problem.

    Lately I've been finding that for every one thing I learn about music, I have to learn at least two more about electronics.
     
  6. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    I don't have a schematic for the Bass 350 but I'm guessing that the tube is long before the effects loop.

    Since you're still getting distortion, my guess is that there is probably an unhappy little transistor in the amp. I recommend that you take it to a good amp tech to put it on an oscilloscope and check it out.

    Good luck! (and keep us posted)