Mesa Nomad head, big hum, help!

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Aahzz, Mar 3, 2006.


  1. Aahzz

    Aahzz Member

    Messages:
    620
    Joined:
    Sep 30, 2005
    Location:
    Greater Cincinnati (Union, KY)
    I just got a used Mesa Nomad, and man does it hum...hums with nothing plugged in at all, increases with volume turned up, and picks up radio stations when the master is cranked...so far, it seems completely independent of preamp settings/channel. Guitar volume changes don't affect the hum at all. I tried a known good tube in V1, as well as different power tubes. I've tried it in different outlets, in different rooms. I've done it without my pedal board, as that was the culprit with my Kustom hum issues.

    Recommendations?

    Anyone recommend a decent tech in Cincy/Northern KY?

    Thanks!
     
  2. Bloozman

    Bloozman Member

    Messages:
    435
    Joined:
    Feb 26, 2006
    Sounds like another swiss watch produced by Mesa Boogie!!:FM
     
  3. Aahzz

    Aahzz Member

    Messages:
    620
    Joined:
    Sep 30, 2005
    Location:
    Greater Cincinnati (Union, KY)
    So poking around in other threads, I tried removing the phase inverter - and that makes the hum go away...methodical preamp tube replacement is comig next....
     
  4. John Phillips

    John Phillips Member

    Messages:
    13,080
    Joined:
    Mar 17, 2002
    Location:
    Scotland
    Sounds like it could be a filter cap failure or a cracked solder joint on one, further down the B+ chain in the preamp supply. That would most likely give the effects you describe. The other main possibility is a broken ground connection somewhere in the preamp.
     
  5. Aahzz

    Aahzz Member

    Messages:
    620
    Joined:
    Sep 30, 2005
    Location:
    Greater Cincinnati (Union, KY)
    preamp tube replacement showed nothing...well, it has decreased somewhat, since V1 was microphonic, and the replacement was ALSO microphonic, dangit...the caps aren't bulging at all, but I don't know enough about discharging caps to mess with them. I took a fair amount of courage on my part to remove the chassis - I've never done that before :). Oddly, the hum increases with the master on channels 1 and 3 - it's immune to master changes on channel 2. As it was just shipped, I'd certainly guess a cracked solder joint could be a possibility, and I should probably find a local tech.
     
  6. Aahzz

    Aahzz Member

    Messages:
    620
    Joined:
    Sep 30, 2005
    Location:
    Greater Cincinnati (Union, KY)
    AH-HAH!!!!

    Played around more with the tubes - I picked up a couple Sovteks this morning, and decided to try them in place of the JJ's the seller had recently put in. With a sovtek in V1, and in the phase inverter, I'm down to the normal, slight hum one expects from a tube amp near a computer. Yay!
     

Share This Page