Hum varies with Volume

Discussion in 'Pickups & Electronics [BG]' started by ttenn, Jan 10, 2009.

  1. ttenn

    ttenn Guest

    Apr 23, 2006
    Just bought a new Ibanez SR755. I've noticed that there is a loud hum when plugged in. The hum continues when the battery is removed (but no string sound).

    The hum is loudest when the volume knob is half-way. With the volume knob all the way up or down, the hum is *almost* gone. If I touch the strings, the bridge, or the cable (to the amp) the hum decreases.

    I opened the control cavity and looked around, but didn't see any loose ground joints. My volt meter shows 0 ohms from the bridge ground to the output jack & volume knob pot case.

    I tried my old bass and no hum, so it's not the cable or the amp. I assume from my search that I have a bad ground. Any ideas on where to start looking?
  2. If it's new why not take it back & get the seller to sell you something that works?
  3. ttenn

    ttenn Guest

    Apr 23, 2006
    It is new, but...

    1. The store is 45 minutes away.
    2. It's the only one they had in stock.
    3. If it is an easy fix, I'd be happy to do it.
    4. I need to play tonight and next week.

    I will take it back if it the pickups or a bad pot, but I was hoping for a little direction that might give me a quick fix.
  4. ttenn

    ttenn Guest

    Apr 23, 2006
    OK, a little more testing...

    I changed the patch cable from the bass to the amp. That helped. Decreased but still present hum that I can now get rid of by turning the treble all the way down.

    Anybody know the short would be if one cable would affect the volume knob, yet another would affect the treble pot?

    Again, this is a stock Ibanez SR755. I have gotten the buzz in three different locations. I don't see any fluorescent/halogen lighting anywhere. A different bass had no buzz with the same cables (including the 'bad' cable above). I opened the control cavity to look around again. Still didn't see any bad solder joints, however I did get a little shock when I grabbed the circuit board. No, I didn't touch the contacts, only the green PCB - static maybe?

    I am definitely gonna take this one back next week. When taking off the bridge to verify the ground connection, two of the four screws at the back of the bridge were broken off at the body. Somebody has taken this bridge off before. It was a 'floor' model.

    Still, I need it tonight and can't get back to the store until late next week....