P bass buzzes with preamp under strange conditions

Discussion in 'Hardware, Setup & Repair [BG]' started by valaka, Oct 19, 2021.

  1. Hi,
    I have a strange problem with buzz. When I plug my player p bass into Ampeg scr-di preamp it buzzes. If i roll the tone knob completely off, the buzz stops. I took pickguard and bridge off to see, whether soldering was ok, and it was. I also took tone and volume knob caps off. After putting everything back the buzz thing changed. Sometimes it creates another (yet similar) additional type of buzz that blends with the old one, if the volume knob isn’t all the way up.
    I tried the pbass with VOX headphone amplug headphone amp and there was NO BUZZ generated by the bass (only white noise that was produced by the amp), regardless of anything I did with the knobs. This headphone amp is powered by batteries. Also tried plugging p bass into my combo amp and it produced only a small amount of buzz when rolling the tone on (the amp has a lot of buzz itself, but the SCR-DI is absolutely silent when cable isn’t plugged in). Then, confused AF, I put my other bass (Ibanez with onboard preamp) into the SCR-DI and it DIDN’T BUZZ at all. I tried plugging the SCR-DI into different socket with the same result.
    Please, do you have any ideas, how to get rid of this terrible buzz?
  2. I also checked grounding with a multimeter, and everything was fine.
  3. Geri O

    Geri O Endorsing Artist, Mike Lull Guitars and Basses Gold Supporting Member

    Sep 6, 2013
    Florence, MS
    Did your meter show continuity between the strings and the body of the output jack?

    A physical inspection of the bridge ground wire might be in order. Sounds like you have intermittent grounding connection somewhere. The connection just happened to be good when you checked.
  4. Yes, it did show continuity. Its not a real multimeter, just a LED and some cable.
  5. Same cable with both basses?
    Our guitar player recently had a buzz/hum with his new amp. He plugged into another amp and there was no buzz. Each amp had a cable already attached. He then switched cables and the buzz was gone. He replaced the instrument cable to fix the issue.
    Just tossing this idea out as a possibility.
  6. Thank you for your effort, but cable was the same.
    One Way likes this.
  7. I checked it multiple times, but it still looks like connectivity is all right.
  8. FrenchBassQC

    FrenchBassQC Supporting Member

    Jul 13, 2011
    Gatineau QC CA
    You removed (unscrewed it from the body) the bridge in order to verify that the wire coming out of the body of the bass was sticking out enough to touch the bridge when the bridge was screwed to the body?
  9. Yup.
  10. Slater

    Slater Leave that thing alone.

    Apr 17, 2000
    The Great Lakes State
    Hafta ask…. …Did you try the Ground Lift switch on the SCR-DI?
    Lownote38 likes this.
  11. Lownote38


    Aug 8, 2013
    Nashville, TN
    That was going to be what I asked. You beat me to it!
    Slater likes this.
  12. Yup
    Lownote38 and Slater like this.