Hum in my SWR 350x-Problem solved

Discussion in 'Amps and Cabs [BG]' started by LoveThatBass, Nov 24, 2004.

  1. Previously I stated a Groove Tube 12AX7R fixed my hum problem..well it was coincidental. I removed the preamp board and inspected solder joints, check Caps for Value and ESR. What it turned out to be was the double stacked Input Jack. The signal was not being grounded when the plug was removed from the Active jack. If I played through the Passive/active jack for more hummed. Matter of fact it hummed with nothing connected. I put a guitar cable plug in the active jack to push it up then I adjusted the contact bar for more downward tension. Problem solved. Looks like this may be a weak link in the SWR amps. Hey, I don't mind...I bought it used at Guitar Center and it appears this may be why the original owner traded it in the day I bought it.
  2. wisdom


    Feb 6, 2006

    The same problem appeared with my Black Beauty combo. (Hum using active and when nothing connected, no hum using passive). I found your article (using Google). So instead of hunting schematics for the amp I checked the contact bars. And it worked! :hyper:

    So thanks a lot!! :)

    Looks like a common problem with these jacks.
  3. Thought I would add this:
    Since my previous post above the problem came back and I found putting a piece of foam rubber under the contacts to act as a spring and provide needed tension to the contacts worked very good. Still ok after a year and two months.