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Bass guitar buzzing when volume knob not at full?

#2
I'd like to know the answer to this, too.

I understand that electrostatic hum/buzz happens and that shielding can help, but why does the hum stop when vol pot is up full, and kick in (for me) at 8 and below?

edit: the hum on my bass is minimal, it doesn't bother me. I've been assured the grounding is good. But I am curious as to why this happens.
 
#7
HCEarwicker said:
No one? Another of the Universe's unfathomable mysteries?
Click to expand...

Not unfathomable.

It's a problem with bad shielding. Perhaps a cheap guitar cable or amp shielding.

It's like this. The amount of hum pickup depends upon the impedance of the circuit. This is why microphones use low impedance to keep hum pickup low since their output is low. The higher the impedance the more hum gets picked up if shielding isn't 100% effective.

It depends on the wiring, but imagine this: A pickup hooked to a volume pot. Now the pickup has a general impedance (consider the resistance of the coil) of a few K Ohms. But the volume pot is usually 250K or 500K.

OK. When the volume is at full, the volume slider is all the way at one end of the pot shorted to the pickup output. Hence the amp is looking at about a 4 or 5K circuit which doesn't pick up much hum. Now move the volume control to the center. Suddenly the impedance seen by the amp may be serveral hundred thousand Ohms which greatly increases hum pickup if say your cord is cheap with ineffective shielding (or less than optimum shielding anywhere in that circuit).

Not all bases do this since some wiring is such that the volume controls short the pickups and for those the impedance to the amp never gets high. Active basses can do this too, but then it's a problem of shielding in the bass rather than the output as they usually have low impedance cable driver circuit that prevents high impedance to the amp.

OK?
 
#10
DethByDoom said:
I have a DeArmond starfire and it does not do this...
Click to expand...

Not even with vol pot at less than 8 and with your fingers making no contact with strings/bridge/pickups (my hum disappears as soon as I touch those things)? Nice! Mine does.

Like I say, the hum is minimal, very. But it is there. It doesn't bother me, cos I usually play with vol up full. Or if both pickups are on, at least one is up full. So I'm not complaining. Just curious.

BTW, I'm using a Planet Waves Custom cable into an SWR (pre-Fender) amp. Which is as expensive as I'm ever likely to get!
 
#12
I fiddled about some more. There's only hum on my bass when -

1) The vol pot [of whichever pup(s) I'm using] is less than 8

2) I'm near my PC

- otherwise there's no hum at all at any setting. Generally.

So I'm thinking the hum is caused by electrostatics in the room being picked up by the bass's wiring/circuitry. It can be reduced with shielding. And bassbenj has explained why it goes away when the vol is up full.

Is that it?
 
#13
Hello all.. I'm curios also.. I just got my Dean Edge Q5 with EMG pickups and it has a slight hum when plugged into my amp. The hum DOES NOT change when i touch metal or strings on the instrument. So i dont think its shielding. If you turn the volume knob on the bass all the way off it still hums..?? My other Dean Edge does not make this noise when plugged into the same amp with the same cable. The new Q5 also seems to have less volume than the other Dean bass, a Q4 with dean standard pickups. Any ideas ? I am going to check wall socket with gfci tester but i dont think that has anything to do with it since the other guitar is not affected the same way.. Thank yall
 
#14
FWIW, I get noticeably more hum when playing my active bass near CFLs. Better shielding might help (conductive paint vs foil?) but it's easier just to keep the bass away from CFLs and dimmer switches. My hum is worse at max volume.

The upcoming ban on incadescent bulbs might increase hum complaints here on TB!?
 
#16
Playing around more the hum actually increases is i turn the treble knob all the way up. When i get like at 9 or 10 with the knob it increases slightly... sounds like constant static. I turned off the lights in the room and speakers on my computer but that does not affect the noise.. Maybe bad ground? Reversed wires?
 

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