Conference napalm::guitar

    It could be a bad ground to the bridge on the bass itself.
    If his bass has single coil pickups, chances are that's where
    the hum comes from. The amount of hum you get with single coil 
    pickups varys depending on your position relative to the amp. 
    If you turn towards the amp the hum increases, turn away it 
    decreases. If you plug into a PA system (especially one with 
    monitors) there is no where he can hide where his pickups won't 
    interact with a speaker.
    
    Usually if you play through an amp, and go from the line output
    into the PA, the amp isolates the hum to the bass and amp, and the
    bass won't interfere with the PA as much. If you have a bass amp
    with a line output, try using it this way and see if it makes a
    differance.
    
    Mark Jacques
    
    

    Thanks.  As a matter of fact, it does have single coil PUs.  I still
    don't quite understand why turning down the VOL control on the bass
    increases the hum, though.  I've seen this problem on other guitars
    & always wondered.
    					joe

Definitely go after the grounding on the bass guitar itself, and the shielding.
I don't know why it seems to only happen with the PA and not another amp but
the problem you describe is a grounding problem.  Grounding problems can be
real subtle, too.  Sometimes a ground just isn't a ground.  Perhaps the
connection of the bass to the PA is not as good a ground as the connection
of the bass to the amp.  Look for ground loops and other antennas in your
bass wiring.  Is there one connection per ground wire to a common point in
the internal wiring (called a star ground)?  Does a higher quality cord help?
Is the problem with the electrical outlets or extension cords?
Where do you keep your stomp boxes in relation to strong electric/magnetic
fields?

I don't think that it is really related to the position of the PA monitors.
Cuz, no matter which amp you play through - on stage you are in close
proximity to the monitors and alot of other E&M fields.  E&M fields are
your enemy.  Your bass doesn't care if they are from the amp that you are
using or the overhead flourescent lights.  And my guess is that the E&M fields
coming out of monitors are not as much as a problem as the E&M fields from
the power transformer on a large amp.  And if you describe the problem as
a hum - that sounds like the good old 60 cycle/second hum in AC.  Maybe you
could jam to it?

    Now that's a thought, just use arrangements that lend themselves
    to 60Hz accompanyment.

	Hi Joe!

	What's happening is that the impedance of the line is
	highest when that pot is not either full on or full off.

	Check that the wiring within the guitar itself is shielded,
	i.e. from the 1/4" jack to the volume pot. How about the
	cavity that the pix and controls are in - shielded with
	foil? Everything that's high impedance must be within the
	"faraday cage" of the shielding, or Hmmmmmmmmmmmm.....

	Good Luck!

	Joe Jas
< Note 983.4 by ROLL::BEFUMO "I chase the winds of a prism ship" >
                             -< Go with the flow >-

    Now that's a thought, just use arrangements that lend themselves
    to 60Hz accompanyment.

    Thanks folks, I'll pass all your info on this evening.
    					joe

    
    
    I don't know why guitars aren't better shielded.  My cheapo Danelectros
    are better shielded than my megabuck axes....at least until I had
    a repairman redo the shielding on them.
    
    My house is wired for two-prong outlets and as a result if I don't
    ground my amps to a water pipe I get some pretty odd hum problems,
    you know, where the thing is dead quiet until you let go of the strings
    for a second.  I've always wondered how studios wired their AC so as
    to avoid hum on the instruments, particularly in this digital recording
    age!!!