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Roland Cube 30 Bass or: Putting a sock in it.

Discussion in 'Electronic Repair' started by N Cook, Sep 18, 2007.

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  1. N Cook

    N Cook Guest

    Reported as fuzzy sound on the bass guitar E string even at relatively low
    levels
    but otherwise fine sound rendition or backing off the bass control .
    Feeding a signal generator in then indeed a distinctly fluttery distortion
    in the range 50 to 70 Hz on top of the wanted output, ok above or below that
    range.
    No external speaker output on this cube and before getting inside to scope
    it or run an external speaker I took the front grille of in case of
    parasitic rattling but no change. But putting a sock in the front/back vent
    tube in the speaker surround cured it.
    Where to go from here ? sci.acoustics.repair ? charge for an old sock ?
     
  2. Arfa Daily

    Arfa Daily Guest

    Interestingly, I have had a similar problem on several Ashdown bass heads.
    Just as you describe, fuzzy distortion at around 44Hz only, otherwise
    sounded fine. On each occasion, it has been really bad joints on one of the
    main smoothing caps - to the point where the cap is effectively not there.
    With a 'scope on the supply rail, just about full level ripple, but
    curiously, not a hint of hum on the undriven audio. Only when that string on
    the bass guitar plucked, or a sig genny put in at that frequency. I
    completely missed the first one that I had doing it, as it sounded perfectly
    well on all other material, so sent it back to the shop. He came back a day
    later armed with a bass guitar, and demonstrated the problem ...

    Arfa
     
  3. Ron(UK)

    Ron(UK) Guest

    I have also had that fault, we call them Trashdowns around here. I agree
    with Arfa that it`s probably a dry joint. Roland combos are generally
    better constructed, or at least, they were!

    I had a similar fault on a Peavey bass combo, and it turned out to be
    air fluttering in the bass port, I presume the speaker had somehow
    deteriorated, a wodge of dacron in the port stopped it temporarily.


    Ron(UK)
     
  4. Meat Plow

    Meat Plow Guest

    Try a different speaker.
     
  5. G

    G Guest

    Well it seems like it could be electronic or mechanical. Putting a sock around
    a vent will usually make the cone move more and create more distortion, if
    that is the problem. I can't believe there is a vent, and a 10 inch guitar
    speaker can't reproduce 50 Hz unless its a HIFI driver. The description about
    speaker surround, baffles me.

    greg
     
  6. N Cook

    N Cook Guest

     
  7. N Cook

    N Cook Guest

    Decoupling the negative black lead (not ground) via a 10u polyester cap to
    the scope ground the electronic trace was fine at all frequencies and
    powers. Semi-permanently blocked off the reflex/bass port or whatever that
    hole is called and the intrusive 50 to 70 Hz induced flutter has gone. Just
    the normal low level flutter , for low frequency, high power output due to
    vortexing/cavitation or whatever the normal distortion due to bulk shifting
    of air mass by a cone is called.
     
  8. Ron(UK)

    Ron(UK) Guest

    N Cook wrote:
    Just
    We call it crapping out ;)
     
  9. Meat Plow

    Meat Plow Guest

    Expecting too much from that amp.
     
  10. PhattyMo

    PhattyMo Guest


    Just normal "port noise" aka "chuffing" ? Mebbe they need to change the
    diameter of the port.
     
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