Series bass noise issue?

[jazzyvee]

I have a 1980 series I shorty. Normally i always use it with the 5 pin cable and DS5. However yesterday i had my little Pjb briefcase out for my practice session, after that grabbed my shorty and it's stereo to mono cable with the resistors in so i get both pickups. But when i turned the bass on i got loud hum that got louder with opening up the filter and q and much less with the filters closed. It also virtually disappeared if i touched either of the the metal jacks. It seems directional also but I'm assuming the cable or one of the jacks plugs may be the culprit, but also wondering if it could be something funny going on with the jack socket on the bass or hum cancelling system.
Any thoughts?

[StephenR]

Did you try the bass through the same rig using the DS5?  That would take the mono cable and 1/4" jack in the bass itself out of the equation. Maybe try a different bass with the same rig/cable, if the problem persists with a different bass then it is most likely something with either the cable or the amp itself Good luck with the troubleshooting, it is most likely something simple...

[jazzyvee]

Thanks for your input Stephen.
Today I tried the same bass through the same PJB Briefcase with DS-5, noise, Same bass using the stereo to mono cable, no noise.
Then tried my regular bass rig separately with the 5pin and the stereo to mono cable and no noise.
A thought came to me just as i started writing this, i used the PJB today on the internal battery power today and not sure if i was using it with the mains power yesterday.
Will try the amp again tomorrow with the mains as it's a bit late here.