Post by Brian RunningGeez, Benj, I was beginning to wonder if you were going to reply or not.
Don't leave me hanging like that.
You and I have been lobbing semi-friendly, sarcastic bombs at one
another for years, I don't really mean them and I don't think you really
do, either, but we have a tradition to uphold. I thought the ball was
in my court after you jumped on me about concealed carry right after you
said you'd vote for me for president, so I felt compelled to lob one
back at you.
OK. :-)
[You actually REMEMBER the crap I say here? Oh my! ]
Post by Brian RunningHere's the thing about the buzz antenna. There's absolutely no doubt
that the human body plays a part in the hum, that's obvious.
Um. sometimes. Plays no role in MAGNETIC hum because the human body is
sort of conductive but not magnetic.
Post by Brian RunningBut, the
problem is that it's not consistent, it's entirely dependent on many
variables in the environment at the particular moment that it happens.
It's not a consistently, reliably-repeatable phenomenon,
Yes, this is true, but I don't know that it's a "problem". I mean the
hum induced into the bass circuit DOES depend on the configuration of
wires in the room, and where the body is (just move the bass away from
your body and observe that (sometimes) the hum will go down. So sure
it's all about position because the "capacitor" made up of the wires
and your body that is coupling into the circuit has a value that
depends on the position of everything.
Post by Brian Runningso it's not
valid to say simply that the human body is a big hum antenna, radiating
induced hum into the pickups.
Well, it is valid to say the human body is a big hum antenna WHEN it
IS a big hum antenna! Of course there are times when it's not acting
that way!
Post by Brian RunningSometimes, there's hum when you're not
touching the strings, sometimes it's the other way around. Sometimes
it's coming in through the power cord, sometimes it's induced in the
lead from bass to amp, sometimes the pickups pick it up directly out of
the air. There are times when the body seems to act as an antenna,
there are times when it seems to block interference.
Yes. And that makes sense if we consider the body to be part of a big
capacitor. What that "capacitor" does to the signal really depend on
how it's "hooked up" and that of course depends on that "configuration
in the room" which is sort of unknown and out of control to a degree.
Post by Brian RunningIt seems to me that RF from CRTs, neon and fluorescent lights are picked
up directly into the pickups, because you can usually null the noise out
by moving the bass into another direction, and touching the strings or
holding the bass near your body makes no difference. But when there's
ground-related noise the body does seem to matter. Touch the strings,
hold the bass away from you, it affects the noise. When the noise comes
in through the power lines or is induced into some cable somewhere, then
pickup position or body don't matter at all.
All the above really is true. But you can separate the effects. There
are three in total. The first two are what I talked about. The first
is capacitive (electrostatic) pickup of hum. This is where the power
wiring (which is not shielded) in the room or to the gear radiates a
hum field which the capacitor formed between the bass circuits and the
unshielded power wiring induces a hum into that circuit. This occurs
because the circuit is high impedance and that allows a VERY small
capacitor to induce substantial hum. All the conductive things nearby
(including bodies) will affect that "capacitor" and therefore the
hum. Usually things like touching the strings will reduce hum because
it grounds out part of the "capacitor" formed by your body, but since
the whole arrangement is sort of random and unknown, there are times
when truly weird effects are observed. I didn't want to get into the
"magic" aspects of shielding but yeah, some truly weird crap can
actually be observed from time to time! such as touching the strings
increasing hum.
The second hum source is magnetic fields right into the pickups. Large
power transformers are the usual culprit since magnetic fields are
caused by heavy currents in wires. These are the opposite of above.
Your body will play NO role in modifying these effects as bodies are
not magnetic. However, one interesting fact is that usually one can
find a position of the bass where magnetic fields are nulled out. This
is sort of like the humbucker idea only it's positional. So if your
bass is humming like mad and if you move it around into different
orientations and you FIND one where the hum goes away (it probably
won't be a position you can play it in!) That often means the noise is
magnetic and can only be eliminated with a humbucker pickup (On a jazz
bass that is both pickups on full or identical volume settings) or
simply getting away from the transformer or other source. Many people
don't realize that the hum blocked by humbucker pickups is NOT the
same hum blocked by copper foil or other cavity shielding! A split
coil P bass IS a humbucker pickup so this is not a problem there. Of
course electrostatic pickup is positionally sensitive too, though you
usually can't find a "null" position where it totally goes away.
The third noise source would be electromagnetic WAVES. These are like
radio waves (and sometimes actually ARE radio waves when you can hear
a radio station through your amp), but usually are Noise waves that
come from various pulsed sources of current. (as you mention some,
crts, neon, fluorescent lights, dimmers, etc.) A pulsed current
actually will generate radio waves due to the large number of
harmonics that short pulses generate. These are true waves that can
bounce around the room and are usually "broadband" which means they
can be picked up on radios or other circuits that act like radios
(which typically is an amp front end that does not have enough rf
filtering on the input. G&L basses are VERY prone to this pickup in
active mode! But happily, the same shielding that works for
electrostatic pickup above, ALSO works to block RF waves as well. So
it's kind of a two-for. BUT RF waves are FAR more insidious and they
crawl all over everything sneak into tiny cracks and holes in
shielding and even will travel down the OUTSIDE of shielded wire! If
there is an RF noise problem "magic" is often required to fix it after
all else fails! :-)
So yeah, you are right there is not ONE thing that works here and
yeah, the problems can be mysterious and complex but happily the
principles of shielding are pretty simple and well known so that once
you get the hum blocked it no longer matters what kind of complexities
are going on out in the room. Wash my mouth out with soap, I think we
agree but just were saying it a bit differently.