VERY odd evelopment

Discussion in 'Amps and Cabs [BG]' started by buldog5151bass, Feb 7, 2017.

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  1. buldog5151bass

    buldog5151bass Kibble, milkbones, and P Basses. And redheads.

    Oct 22, 2003
    Connecticut
    I have a Carvin BX-500. Very recently, it started making a loud hiss, and louder when I plug in an instrument.
    I tried the usual - deoxit on the ribbon cable connectors - no change.

    But HERE is where is where it gets weird. When I plug in a pedal (Ibanez Tube Screamer) - no hiss. The pedal is in the chain, not the effects loop. I have no idea why that would make the noise go away.

    Any ideas???
     
  2. Cable maybe?
     
  3. buldog5151bass

    buldog5151bass Kibble, milkbones, and P Basses. And redheads.

    Oct 22, 2003
    Connecticut
    I've tried several cables.
     
  4. Bass > Pedal > Amp, and the bass plays fine and all is as it should be?
    Bass > Amp and you only get hiss? Or bass plays normally + hiss? Or bass sounds funny in spite of the Hiss?
    Active or passive bass?
     
  5. buldog5151bass

    buldog5151bass Kibble, milkbones, and P Basses. And redheads.

    Oct 22, 2003
    Connecticut
    Bass } pedal } amp = everything is normal
    Bass } amp = bass plays normal, but with hiss
    Amp unplugged = hiss, but much softer

    Passive jazz bass
     
    PortlandBass77 and Felken like this.
  6. What happens when the pedal is in the loop, but is bypassed?

    I'm not an amp tech in the slightest, but I wonder if you have some sort of ground loop/issue that somehow corrects itself with the pedal in the circuit.

    Have you tried the amp in any other outlets, circuits, or even in any other buildings?
     
  7. basscooker

    basscooker Commercial User

    Apr 11, 2010
    Northern KY
    Cab fan, hobbyist
    Pickup shielding? Need a new ballast for a florescent light in the room? Something new plugged into the outlets? Random stabbing here...

    Is the pedal run on a wall wart that could be serving as a ground, and the problem is a loose ground somewhere inside the amp?
     
    HolmeBass likes this.
  8. basscooker

    basscooker Commercial User

    Apr 11, 2010
    Northern KY
    Cab fan, hobbyist
    Ok, I have another one. Maybe even further out there.

    Run bass>amp, but wrap another (disconnected) instrument cable or speaker cable in a loose coil around the instrument cable, then speaker cable, then power cable. If any of that makes a difference, it could be RFI. Unlikely, but why not.

    Edit.... Could it be the ground wire from the pickups? IDK what your bass or bridge is, but have you used polish or anything that could have worked its way under there and be affecting the pup/bridge connection?
     
  9. Does the Tube Screamer take batteries and a 9vdc power supply? If you're using the power supply, what happens when you run it off a 9v battery?
     
  10. two fingers

    two fingers Opinionated blowhard. But not mad about it. Inactive

    Feb 7, 2005
    Eastern NC USA
    Try any other bass or guitar with a 1/4" jack and get back to us. Any other one will do.

    Also, take your bass and rig to any guitar shop or a friend's out and try it out there. There are too many variables that have not been removed as possibilities to narrow it down yet. If you happen to do it in a guitar shop, take every single piece out of the chain until you narrow it down to the culprit.
     
    megafiddle likes this.
  11. Ground loops cause hum, not hiss. Unless he meant hum when he said hiss?
    Hum is spelled mmmmmmmmmmmmmmmmm.
    Hiss is spelled sssssssssssssssssssssssssssssss.
     
    Last edited: Feb 8, 2017
  12. Stabbing doesn't make a hiss sound.
    It often sounds like YAHHHHHHHH, and then possibly silence.:smug:
     
  13. Good point.
     
  14. basscooker

    basscooker Commercial User

    Apr 11, 2010
    Northern KY
    Cab fan, hobbyist
    Agreed. That monkey-wrenches most of my hypotheses.

    Bully, have you swapped speaker cables too?
     
  15. Spidey2112

    Spidey2112

    Aug 3, 2016
    Maximum Output: Level 0dBm
    Maximum Gain: + 30dB
    Equivaient Input Noise: -100dBm (IHF-A)

    These are spec #'s from Sweetwater, for the Tube Screamer. May be why it quiets the hissing...

    Anything else happen around the time you started noticing the unwanted sound?

    If you can, pop it open and check out your instrument jack for the amp... it's usually the simplest things.
     
  16. megafiddle

    megafiddle

    May 25, 2011
    Hiss is caused by active components, and is often occurs in the first stages of an amplifier, where it is amplified by later stages along with the input signal.

    This noise (hiss) is usually in the form of a noise current, and therefore the noise voltage (which is what gets amplified) is dependant on the total input impedance which includes the source: noise voltage = noise current x impedance. That's why the hiss is less with a low impedance pedal output driving the amp.

    The problem is in the amp input stage.

    -
     
    Last edited: Feb 7, 2017
  17. two fingers

    two fingers Opinionated blowhard. But not mad about it. Inactive

    Feb 7, 2005
    Eastern NC USA
    I like it.

    Get that head to a guitar shop and try it with other passive basses. If this (seems plausible) theory is true, it will happen with any passive bass into any cab.
     
  18. yodedude2

    yodedude2 Supporting Member

    Nov 19, 2005
    san antonio, texas
    i'm with twofer on this. the head with other instruments? the bass with other amps?
     
  19. fdeck

    fdeck Supporting Member Commercial User

    Mar 20, 2004
    Madison WI
    HPF Technology LLC
    Very long time ago, I repaired a compressor that got hissy in one channel. That channel turned out to have a bad op amp chip, which I replaced, and the hiss went away. There's also the possibility of something like a cold solder joint or broken solder joint around the input connector causing a high impedance situation. I always warn people that digging into mains powered gear can be dangerous, and should be done by a qualified technician. If I were that technician, the first thing I'd look for is any kind of loose connection or bad solder joint in the input circuitry.
     
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  20. organworthyplayer337

    organworthyplayer337 Professional Hack

    Oct 28, 2014
    Charlotte, NC
    Ahhh nice new fingers, Two Fingers :smug:
     
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