Discussion in 'Amps and Cabs [BG]' started by Lowbrow, May 17, 2021.

  1. Lowbrow

    Lowbrow Supporting Member

    Apr 22, 2008
    Pittsburgh PA!
    OK so when using my all-tube Ashdown Little Bastard suddenly I got a little electronic noise --- nothing hairy, sounded like a bad cord connection like you might get when you step on/pull your cable -- and then the volume dropped significantly.

    No amount of my usual go-to fix --- pounding on the amp with my fist --- made any difference or elicited any alarming noises. Turning amp on and off made no diff. Still get sound but not much power. Tone knobs have effect; volume has an effect. No bad smells or crackling.

    Guidance, oh my genius pals?
    mikewalker likes this.
  2. rickdog

    rickdog Gold Supporting Member

    Mar 27, 2010
    Try plugging your bass into the effects return jack, does that make a difference? There's a switch in the effects send jack that routes the signal internally when there's nothing plugged into those jacks, it could have developed a little bit of corrosion.

    Have you tried some methodical troubleshooting and fault isolation? Different bass, cable from bass to amp, speaker cable, speaker?

    My first thought was a tube has failed. But before you go there, check all those easy things first.
    mikewalker likes this.
  3. Lowbrow

    Lowbrow Supporting Member

    Apr 22, 2008
    Pittsburgh PA!
    Thanks, I’ll try that. Remembered this: prior to the volume dropping out I engaged the amp’s mute function. When I flipped the mute off the problem described was there.
  4. Wasnex


    Dec 25, 2011
    Here is the signal path. Input Jack, V3a, effects loop, V3b, bass shift/tone stack, V2b, V2a, mute switch/bright switch, volume control, phase inverter (V1ab), output tubes.
    PaulCISSA and S.F.Sorrow like this.
  5. Lowbrow

    Lowbrow Supporting Member

    Apr 22, 2008
    Pittsburgh PA!
    Thanks - but I’m a non technical type. What does that tell me?
  6. Wasnex


    Dec 25, 2011
    The effects loop is very early in the amp. So if you plug into the effects return and it fixes the problem, it's V3B or the effects loop itself. I believe both the Send and Receive jacks are both switching. The switching contact in either jack can get dirty or bent. Running a 1/4" cable in the effects loop should bypass the switching.

    About the only thing you can do is check the effects loop and roll a new tube through the amp. Also the amp has two inputs (High and Low). One input is padded down more than the other, but both should work. ]

    The mute switch grounds out the signal at the volume control. Does the mute switch still work to turn the signal on and off?
    S.F.Sorrow and rodl2005 like this.
  7. 808State

    808State Inactive

    Dec 30, 2020
    He had issues after using the mute switch.

    So with regards on a million internet guessing.

    Its likely to be a issue with the mute switch.
    Either the actual mechanical connections inside the switch.
    Or the solder connections on the board from the switch.

    Random volume dropout with amplifier in a generalized sense.
    Usually associated with the mentioned effect loop issue.
    Usually dirty contacts, bad solder connections with the effect loop jacks.
    Dirty volume pots
    Dirty input jacks/ failed solder connections with input jacks.
    Bad mute/ pad switches mechanical / or board connections.
  8. rickdog

    rickdog Gold Supporting Member

    Mar 27, 2010
    I have a CTM-30, not a Little Bastard; but I think they're the same amp in a different package. On my CTM-30, it's the Send jack that has the switch; the Return jack does not. I know this because if I plug a tuner into the Send jack, it mutes the amp, but if I plug it into the Return jack it does not mute the amp and the tuner gets signal. Never understood why they did it that way. It's a lot more useful if the Return jack has the switch.
    Wasnex likes this.
  9. Wasnex


    Dec 25, 2011
    It is more common for the Return jack to be switched so the Send can be used as a slave out.

    AFAIK the CTM30 and the original LB30 are the same circuit. The Little Stubby is a bit different.

    Here is the part of the LB30 schematic that deals with Effects Loop.
    You're correct, the Send appears to kill the signal from the input, but the Return does not. AFAIK this is a bit unusual.

    Here is how the Trace Elliot series I V-Type effects loop is wired.
    This appears to show the Return kills the signal from the input, but the Send does not. The normal type of switching, and I agree this would be more useful.

    Attached Files:

    S.F.Sorrow and rickdog like this.
  10. Lowbrow

    Lowbrow Supporting Member

    Apr 22, 2008
    Pittsburgh PA!
    Yes, mute switch still works as do EQ knobs and volume knobs as mentioned. Have not opened chassis but can see all 4 tubes lit. I will try the effects loop later in the day —Thanks all for your help.
    Last edited: May 18, 2021
    Wasnex likes this.
  11. 4dog


    Aug 18, 2012
  12. Lowbrow

    Lowbrow Supporting Member

    Apr 22, 2008
    Pittsburgh PA!
    • Plugging into the effects send OR return does not improve output.
    • Mute continues to engage and disengage as mentioned.
    • While all three EQ knobs affect sound somewhat, the TREBLE knob has a far greater effect than the other two (this is the sort of tone stack that will silence the amp completely if all knobs are rolled to zero)
    From what I do know about how amps work -- weird action of the treble knob aside -- this points to the preamp section pretty much working and power section not working. I GUESS.
    Last edited: May 18, 2021
  13. S.F.Sorrow


    Dec 6, 2014
    It could just be a bad tube. Especially if your "usual go-to fix" is pounding your amp with your fist! If this is something you've actually done on a regular basis with you amp switched on I would honestly be more surprised if all the tubes are still ok...
  14. Lowbrow

    Lowbrow Supporting Member

    Apr 22, 2008
    Pittsburgh PA!
    HA. No, I'm an adult, and have been for 38 years.
    Murch and S.F.Sorrow like this.
  15. I'm a recent convert to the 'contact cleaner fixes everything,' ideology. I'd get some electronics contact cleaner, unplug and then open up the unit, hose down all the pots while rotating them, let the thing sit for a day, clean it up, close it up and try again. That worked with my EHX English Muff'n, Ernie Ball Valve Jr., and Peavey Alphabass.

    Edit, leave the unit set for a while between the 'unplug' stage and 'open up' stage. Caps can take a bit to discharge.
  16. Laurent

    Laurent Supporting Member

    May 21, 2008
    Napa, California
    I have one of these amps. Great little tone machine!
    Check your tubes.
    FronTowardEnemy likes this.
  17. S.F.Sorrow


    Dec 6, 2014
    Lol, that's good to know. It might still be a tube though. At least that's what I would try first, simply because it's the easiest thing to eliminate. Anything more serious will probably need to be diagnosed (and fixed) by a tech.
    Lowbrow likes this.
  18. 2112


    Apr 30, 2005
    Did you try putting foil on the rabbit ears?
    Spidey2112 and Lowbrow like this.
  19. FronTowardEnemy

    FronTowardEnemy It is better to go unnoticed, than to suck Supporting Member

    Sep 19, 2006
    Chicago Illinois
    Hope you get it sorted out. I love my LB30. Let us know what you find out.

    BTW Ashdown has enough parts to make 8 more LB30s listed on their website.

    Was thinking about ordering a UK made one because I love it so much.
    GroovyBaby likes this.
  20. We used to pound an amp with our fist to make the reverb spring noise.:roflmao:
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