Conference napalm::commusic_v1

    >simply
    >connecting the speakers to the PA head (not even powered up), causes a
    >loud and noticable hum. Turing the head on, does not change the hum.
    
    This is a new one on me.  The most frequent cause of hum is grounding
    differential, which can be cured by all amps being plugged into the
    same circuit.  This sounds like induced DC hum, maybe you can re-route
    your speaker cables, or maybe shield them ?
    
    karl

    It's not uncommon if there is a lot of RF generated, for speakers to
    pick it up.  A buddy of mine who works for Bose told me of a service
    complaint that was tracked to being in a building which had a number of
    broadcast antennas on its roof.  A sound system on the top floor was
    picking up the audio from different TV channels, just sitting in the
    room, unplugged!
    
    I would try a line filter, since the noise may be getting into the AC,
    thus the path is through the AC cord, power supply and out to the
    speakers, even though the power isn't on.
    
    						Brian

	Oh sure, any gas discharge tubes can hum up a storm.
	Too bad there is no differential audio spec.
	Use short grounded-shield cables everywhere, esp. on the line level
	cables.  dress your cables as far as possible from the neon lights
	and their circuits. However, line filtering is awfully hard at 60 	
	and 120 Hz.  Do the boxes even do this?  If you filtered out 60 Hz,
	you'd have no power!  Use high levels on the line to up the sig/noise.
	Clean all connectors of corrosion.  
	Plug into one place.
tom

    I have a similar problem with my two OB-Xa synths, regardless of where
    I might be.  These units pick up an INCREDIBLE amount of noise thru
    ground.  The solution is simple - use a ground lift per unit.
    
    One fairly simple suggestion ... have you tried moving your amps at
    all?  If the noise is due to the lights, trying picking up the amp and
    moving it around a few feet each way (assuming you have enough extra
    cable).
    
    Another idea - depending on how (in)competently the place was wired,
    you just might be on the same circuit as the lights (or at least on a
    common ground or {gasp!} neutral).  Get a good extension cord and try
    another receptacle.  A good power conditioner might also help, but
    given the situation you describe, it would have to be a high end unit
    to handle the noise ... and those aren't cheap.
    
    Finally, if the problem is due to dirty power, then I would answer a
    definite "YES" to the "is my gear at risk?" question.
    
+b (back after 3 weeks off 8-)

    Hi,
    
    Thanks for the quick response and thanks especially for confirming that
    what I'm hearing can in fact happen. In my 20 or so years of playing,
    I've never encountered this situation where the hum (noise??) appears
    in the speakers simply by connecting the speakers cables...
    
    anyway, the building is about 100 years old and is a converted private
    house. the owner still lives upstairs. The electrical wiring is a mess,
    I'd suppect it's been modified/upgraded a dozen times thru the years.
    I believe Murphy is alive and well in that wiring, if it can be wrong,
    it is.
    
    All your suggestions make good sense, unfortunatly, I can't implement
    most of them. Moving the equipment is not possible due to the serious
    shortage of room in the place. I could try plugging into another outlet
    as a test, however, would have to run an extension accross active
    walkways. 
    
    Being a starving musician, expensive filtering systems are currently
    not in the budget, i would be willing to take a shot at line filters
    etc. if they can be had reasonably.
    
    I am using 50 ft, unshielded speaker cables, to go about 5-7 feet. The
    excess is coiled, and dropped on the floor below the speaker stand. 
    I am going to try using shorter and shielded cables this weekend and
    see if that helps the situation, I guess I am providing a pretty
    good antenna.
    
    Thanks again for your help, please feel free to offer any additional 
    suggestions, I'll let you know if the shorter cables help.
    
    PS re:.2 thank your friend at Bose, i must have looked pretty stupid
    standing there staring at my speakers with a dumb look on my face.
    
    Gary
    
    

    Gary - have you tried plugging in the speaker cables WITHOUT connecting
    them to the amp?  (In other words, all that you have is cables
    connected to speakers.)  I suspect that the noise is being picked up by
    the amp or something else upline, not by the *speaker* cables.
    
    Have you tried checking instrument/mic cables?  Noise in a shorted or
    unshielded cord (which is in the preamp-stage) will amplify like crazy. 
    I remember that we had something weird like this happen once even when
    the amp was off ... I think it was due to a combination of an
    instrument needing a ground lift and a guitar cord being marginal, but
    it's been *years*.
    
    Anyway, if you don't get noise without being connected to the amp, the
    first thing I'd try is a ground lift (3-prong to 2-prong adapter) on
    the amp's power cord (if you haven't already - I wasn't certain from
    reading .0).  If the ground lift works, lift a power strip and plug all
    your gear into the strip.
    
    If you still get noise with a ground lift (and with NOTHING plugged
    into the amp's inputs), you've got dirty power or lots of RF, and the
    only solutions I can think of are:
    
    	o  get a good noise filter (I am somewhat dubious as to the
    	     effectiveness of one at this point)
    
    	o  try another circuit (outlet) - you might not be able to
    	     do this for the gig itself, but you'll at least know if it's
    	     power or RF
    
    	o  try making a shield for the amp by wrapping tin foil around a
    	     large cardboard box and placing it over the amp (make sure
    	     there's enough room for cooling!)
    
    	o  get another gig (if there's THAT much RF running around, I'd be 
    	     reluctant to even go in the place)
    
    One more fairly obscure possibility that just came to mind ... try
    switching plugs on the receptacle; i.e., if you're plugged into the
    bottom one, try the top instead - or if it's a two-gang outlet (2
    recepts side-by-side), try the other receptacle.  It *is* possible to
    wire one half of a receptacle to one circuit and the other half to
    another (I've seen it done before when I used to do electrical
    contracting) - it is also possible that each recept in a 2-gang is on a
    different circuit.  It's a remote possibility, granted, but it's worth
    a shot - and cheaper than a line conditioner.
    
+b

  Maybe this is a good place for this, instead making a new topic:

  Anyone recommend a good line "conditioner", that is provide constant
  voltage output, and filter RFI/EMI, not just protect against spikes/surges?

  The Furman AR-117 good a good review in Keyboard or EM, it can be had for
  around $400.

  Digital resells Uninteruptable Power Supplies, which from what I can
  understand, protect, filter, and condition ... with the added benefit
  of providing x minutes of uptime after a power outage to give you time
  to backup data/shut-down nicely.  With an employee purchase discount, this
  may be a cost effective alternative.  I'm checking into now myself...
  I'll be back...

-Tom

    Re: .7
    
    Juice Goose makes a line of conditioners as well, in similar price
    range to Furman.  Make sure you get plenty of excess amperage to allow
    for adding more stuff to your setup.
    
    						Brian
    

	I have a Tripp-Lite power conditioner... 1.8KW, 6 outlets. Each set
	of outlets has a different noise attenuation rating, range is from
	-30dB to -72dB. Output voltage is regulated to some serious tolerance
	that I forget. 

	List is about $370. I think I paid $329. 

	/pjh

    a few comment about a few tips mentioned earlier...
    
    Plugging one surge protected power strip into another diminishes the
    protection.
    
    Lifting the ground on a surge protecting power strip eliminates any
    protection.
    

    Hi,
    I'm back....this past weekend, i set up early, while the place was
    quiet. Armed with shieled cables, 3-2 adapters, extension cords I
    approached this noise problem like a man on a mission....guess what...
    nothing helped.
    
    The speakers pick up and reproduce the hum, just sitting there. No
    cables nothing, plugging the cables in and powering up the head just
    adds to the problem.
    
    I tried the shielded speaker cables, no help.
    I tried every conceviable combination or isolation via 3-2 adapt's,
    I tried removing all 3-2's, no help
    I tried plugging into the other outlet of the duplex box, no help
    I chanted ancient Indian mantra's...no help
    I tried gounding the two amps together via jumper, no help
    
    I have not tried another outlet, but at this point doubt it will help.
    
    
    Aside from this problem, this is a great gig, I guess i'll learn to
    filter this out of my hearing range.....
    
    Thanks for all your help, I'll continue to try any suggestion you
    may have...please comment..
    
    regards,
    gary
    	

    Is noise affected by the lights that are on?  Standard practice is to
    turn off any nearby fluorescent lights and go with incandescent.  Look
    for anything that has a transformer in it that has power to it all the
    time.  Check out the doorbell, maybe?  The fridge?  Could be lots of
    things putting noise on the lines.  Unplug everything and turn
    everything off to see if you can get things quiet.  If all is dead and
    it's still noisy, maybe you have a neighbor with a VT240 hooked up.
    Ooops ...  forget I said that ...
    
    Steve

Hi,

	Try bringing a gas-powered generator with you, and use that
	for your power supply!  That should eliminate "neon" noise,
	if the problem is inherent in the power lines there.  Then
	again I would think that generator noise would be worse!

_John_

    Geeze guys,
    
            If his speakers pick up and reproduce this hum WHILE NOT
    PLUGGED IN TO ANYTHING, then the noise is being radiated, not
    conducted. All the fancy filtering/grounding is the world will not get
    rid of the noise. I'd guess you'd have to live with it, unless you
    could convince the owner to turn off all his nice lights!
    
    	Frank 

You could also put a high-pass filter (70Hz or so) on the speakers and live 
without being able to shake people's stomachs with your killer bass.

Or use wireless speakers?

How about using 3-conductor shielded wire (with 2 conductors plus shield rather
than just coaxial 2-conductor) for the speakers and grounding the shield?

Burns

    Gawd, if the speaker lines are picking up enough radiated noise to
    drive the speakers to audible levels, I'm not sure I'd want to be in
    that room ...
    
    len.
    

    re: .16
    
    JUST what I was thinking!  If there's that much electromagnetic
    radiation around, I wouldn't want to be there.  Everyone seems stuck on
    the idea of lights causing this, but I've never heard of anything that
    severe caused by lights.  Sounds more like there's a radio broadcast
    antenna very nearby to me.  Can you eliminate it by turning something
    off?
    
    I used to work for EPA and the people that worked across the hall from
    me were in the measurement and monitoring section of the Non-Ionizing
    Radiation Division.  Pretty interesting stuff (certainly much moreso
    then the drivil *I* worked on...).  They told some pretty hairy tales
    about some of the places they measured, said it was so strong you could
    feel it on your skin...
    
    Greg

There was a navy Lab in the Washington D.C. area with field strengths that
were measured in volts per meter. I wonder if any research was conducted
on the staff of that lab?

RE: .11 (gary), .16 (len), .17 (greg)
    
    Like I said in .6, I'm with Len & Greg - if ambient RF is causing your
    speakers to make noise, I'd get outta there FAST ... screw the gig.  
    
    I'm sure you've checked this already, but is there a possibility that
    the noise exists *apart* from your speakers?  In other words, have you
    tried listening for the noise with no speakers in the room?  Have you
    tried taking one of your home stereo speakers in to see if they exhibit
    the same behavior?
    
+b

    
    
    Have you checked to see whether they have wires connected to their
    fluorescents?  Maybe the owner is a big Tesla (the original) fan???
    
    No matter what the source of the noise is, this gig isn't a good long
    time thing...
    

    re .18 - actually, volts per meter is no big deal; static fields
    routinely build up field strengths of kilovolts per meter, especially
    over small distances.  The breakdown voltage of air, i.e., what it
    takes to make a spark, is about 30 KV/cm, or about 75 KV/inch, or
    about 3 *megavolts*/meter.
    
    It's not so much the field strength in volts/meter as much as it is
    the frequency and power density that scares people about exposure to
    high intensity RF, although even 60 Hz fields generated by high tension
    power lines have come under suspicion recently.
    
    len.
    

    Hey is this gig at the Springfield power plant or something.  Did I get
    this right these speakers are making noise when they are not connected
    to anything????(insert the Twilight Zone theme) Either you need an 
    exorcist or you got some Mega Magnetic fields in that place.
    	Any problems with glowing after the gig....8^)
    	At least you'll be an inexpensive night light....8^)
    
    
    
    P.K.

Any way to measure the EMI level ?  Call the FCC maybe (anonymously) ?

My brother used to work in a microwave plastic flow-molding shop.  People there
had been known to notice their belt-buckles heating up.

The FCC made them install some kind of baffling in their ceiling to avoid
screwing up aircraft navigation.

    Yeah!  Let the airlines use their OWN microwaves to heat up food!
    
    Steve